[PATCH 0/9] Re-think the stance towards image format probing
Few recent changes broke wrong, but apparently widely used configurations as used didn't really record the image format into the image. It turns out we can safely probe the image format in few limited circumstances which on the other hand should fix the majority of the problems. Please see patch 8/9 for further explanation. Peter Krempa (9): util: storagefile: Drop image format probing by file suffix virStorageFileGetMetadataRecurse: Remove impossible error report virStorageFileGetMetadataRecurse: Shuffle around assignment of backing chain depth virStorageFileGetMetadataRecurse: Expect NULL src->path virStorageFileGetMetadataRecurse: Use virHashHasEntry instead of fake pointers virStorageFileGetMetadataRecurse: Extract storage access virStorageFileGetMetadataRecurse: Remove 'cleanup' label virStorageFileGetMetadataRecurse: Allow format probing under special circumstances WIP: Add tool for probing images src/util/virstoragefile.c | 231 ++++++++++++++++++-------------------- tests/Makefile.am | 13 ++- tests/qemublockprobe.c | 130 +++++++++++++++++++++ 3 files changed, 251 insertions(+), 123 deletions(-) create mode 100644 tests/qemublockprobe.c -- 2.24.1
Probing by file suffix was meant to be a last resort if probing by contents fails or is not supported. For most formats we never specified any suffix. There's a few formats implementing both magic bytes and suffix and finally DMG which had only suffix probing. Since suffix probing is nowhere reliable and only one format depends on in whic has a comment that qemu doesn't do the probing either drop the whole infrastructure. Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 58 ++++++++++++--------------------------- 1 file changed, 17 insertions(+), 41 deletions(-) diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index 9347c7ab30..4d2e39246c 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -146,12 +146,10 @@ struct FileEncryptionInfo { int payloadOffset; /* start offset of the volume data (in 512 byte sectors) */ }; -/* Either 'magic' or 'extension' *must* be provided */ struct FileTypeInfo { int magicOffset; /* Byte offset of the magic */ const char *magic; /* Optional string of file magic * to check at head of file */ - const char *extension; /* Optional file extension to check */ enum lv_endian endian; /* Endianness of file format */ int versionOffset; /* Byte offset from start of file @@ -297,17 +295,17 @@ static struct FileEncryptionInfo const qcow2EncryptionInfo[] = { }; static struct FileTypeInfo const fileTypeInfo[] = { - [VIR_STORAGE_FILE_NONE] = { 0, NULL, NULL, LV_LITTLE_ENDIAN, + [VIR_STORAGE_FILE_NONE] = { 0, NULL, LV_LITTLE_ENDIAN, -1, 0, {0}, 0, 0, 0, NULL, NULL, NULL }, - [VIR_STORAGE_FILE_RAW] = { 0, NULL, NULL, LV_LITTLE_ENDIAN, + [VIR_STORAGE_FILE_RAW] = { 0, NULL, LV_LITTLE_ENDIAN, -1, 0, {0}, 0, 0, 0, luksEncryptionInfo, NULL, NULL }, - [VIR_STORAGE_FILE_DIR] = { 0, NULL, NULL, LV_LITTLE_ENDIAN, + [VIR_STORAGE_FILE_DIR] = { 0, NULL, LV_LITTLE_ENDIAN, -1, 0, {0}, 0, 0, 0, NULL, NULL, NULL }, [VIR_STORAGE_FILE_BOCHS] = { /*"Bochs Virtual HD Image", */ /* Untested */ - 0, NULL, NULL, + 0, NULL, LV_LITTLE_ENDIAN, 64, 4, {0x20000}, 32+16+16+4+4+4+4+4, 8, 1, NULL, NULL, NULL }, @@ -316,7 +314,7 @@ static struct FileTypeInfo const fileTypeInfo[] = { #V2.0 Format modprobe cloop file=$0 && mount -r -t iso9660 /dev/cloop $1 */ /* Untested */ - 0, NULL, NULL, + 0, NULL, LV_LITTLE_ENDIAN, -1, 0, {0}, -1, 0, 0, NULL, NULL, NULL }, @@ -324,50 +322,50 @@ static struct FileTypeInfo const fileTypeInfo[] = { /* XXX QEMU says there's no magic for dmg, * /usr/share/misc/magic lists double magic (both offsets * would have to match) but then disables that check. */ - 0, NULL, ".dmg", + 0, NULL, 0, -1, 0, {0}, -1, 0, 0, NULL, NULL, NULL }, [VIR_STORAGE_FILE_ISO] = { - 32769, "CD001", ".iso", + 32769, "CD001", LV_LITTLE_ENDIAN, -2, 0, {0}, -1, 0, 0, NULL, NULL, NULL }, [VIR_STORAGE_FILE_VPC] = { - 0, "conectix", NULL, + 0, "conectix", LV_BIG_ENDIAN, 12, 4, {0x10000}, 8 + 4 + 4 + 8 + 4 + 4 + 2 + 2 + 4, 8, 1, NULL, NULL, NULL }, /* TODO: add getBackingStore function */ [VIR_STORAGE_FILE_VDI] = { - 64, "\x7f\x10\xda\xbe", ".vdi", + 64, "\x7f\x10\xda\xbe", LV_LITTLE_ENDIAN, 68, 4, {0x00010001}, 64 + 5 * 4 + 256 + 7 * 4, 8, 1, NULL, NULL, NULL}, /* Not direct file formats, but used for various drivers */ - [VIR_STORAGE_FILE_FAT] = { 0, NULL, NULL, LV_LITTLE_ENDIAN, + [VIR_STORAGE_FILE_FAT] = { 0, NULL, LV_LITTLE_ENDIAN, -1, 0, {0}, 0, 0, 0, NULL, NULL, NULL }, - [VIR_STORAGE_FILE_VHD] = { 0, NULL, NULL, LV_LITTLE_ENDIAN, + [VIR_STORAGE_FILE_VHD] = { 0, NULL, LV_LITTLE_ENDIAN, -1, 0, {0}, 0, 0, 0, NULL, NULL, NULL }, - [VIR_STORAGE_FILE_PLOOP] = { 0, "WithouFreSpacExt", NULL, LV_LITTLE_ENDIAN, + [VIR_STORAGE_FILE_PLOOP] = { 0, "WithouFreSpacExt", LV_LITTLE_ENDIAN, -2, 0, {0}, PLOOP_IMAGE_SIZE_OFFSET, 0, PLOOP_SIZE_MULTIPLIER, NULL, NULL, NULL }, /* All formats with a backing store probe below here */ [VIR_STORAGE_FILE_COW] = { - 0, "OOOM", NULL, + 0, "OOOM", LV_BIG_ENDIAN, 4, 4, {2}, 4+4+1024+4, 8, 1, NULL, cowGetBackingStore, NULL }, [VIR_STORAGE_FILE_QCOW] = { - 0, "QFI", NULL, + 0, "QFI", LV_BIG_ENDIAN, 4, 4, {1}, QCOWX_HDR_IMAGE_SIZE, 8, 1, qcow1EncryptionInfo, qcowXGetBackingStore, NULL }, [VIR_STORAGE_FILE_QCOW2] = { - 0, "QFI", NULL, + 0, "QFI", LV_BIG_ENDIAN, 4, 4, {2, 3}, QCOWX_HDR_IMAGE_SIZE, 8, 1, qcow2EncryptionInfo, @@ -376,12 +374,12 @@ static struct FileTypeInfo const fileTypeInfo[] = { }, [VIR_STORAGE_FILE_QED] = { /* https://wiki.qemu.org/Features/QED */ - 0, "QED", NULL, + 0, "QED", LV_LITTLE_ENDIAN, -2, 0, {0}, QED_HDR_IMAGE_SIZE, 8, 1, NULL, qedGetBackingStore, NULL }, [VIR_STORAGE_FILE_VMDK] = { - 0, "KDMV", NULL, + 0, "KDMV", LV_LITTLE_ENDIAN, 4, 4, {1, 2, 3}, 4+4+4, 8, 512, NULL, vmdk4GetBackingStore, NULL }, @@ -707,20 +705,6 @@ virStorageFileMatchesMagic(int magicOffset, } -static bool -virStorageFileMatchesExtension(const char *extension, - const char *path) -{ - if (extension == NULL) - return false; - - if (virStringHasCaseSuffix(path, extension)) - return true; - - return false; -} - - static bool virStorageFileMatchesVersion(int versionOffset, int versionSize, @@ -842,14 +826,6 @@ virStorageFileProbeFormatFromBuf(const char *path, "Please report new version to libvir-list@redhat.com", path, virStorageFileFormatTypeToString(possibleFormat)); - /* No magic, so check file extension */ - for (i = 0; i < VIR_STORAGE_FILE_LAST; i++) { - if (virStorageFileMatchesExtension(fileTypeInfo[i].extension, path)) { - format = i; - goto cleanup; - } - } - cleanup: VIR_DEBUG("format=%d", format); return format; -- 2.24.1
On 2/17/20 11:13 AM, Peter Krempa wrote:
Probing by file suffix was meant to be a last resort if probing by contents fails or is not supported. For most formats we never specified any suffix. There's a few formats implementing both magic bytes and suffix and finally DMG which had only suffix probing. Since suffix probing is nowhere reliable and only one format depends on in whic has a
which
comment that qemu doesn't do the probing either drop the whole infrastructure.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 58 ++++++++++++--------------------------- 1 file changed, 17 insertions(+), 41 deletions(-)
@@ -324,50 +322,50 @@ static struct FileTypeInfo const fileTypeInfo[] = { /* XXX QEMU says there's no magic for dmg, * /usr/share/misc/magic lists double magic (both offsets * would have to match) but then disables that check. */ - 0, NULL, ".dmg", + 0, NULL, 0, -1, 0, {0}, -1, 0, 0, NULL, NULL, NULL },
Is it even worth keeping the dmg entry around? But deleting it (if appropriate) should be separate from this patch. Reviewed-by: Eric Blake <eblake@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
On Wed, Feb 19, 2020 at 09:18:40 -0600, Eric Blake wrote:
On 2/17/20 11:13 AM, Peter Krempa wrote:
Probing by file suffix was meant to be a last resort if probing by contents fails or is not supported. For most formats we never specified any suffix. There's a few formats implementing both magic bytes and suffix and finally DMG which had only suffix probing. Since suffix probing is nowhere reliable and only one format depends on in whic has a
which
comment that qemu doesn't do the probing either drop the whole infrastructure.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 58 ++++++++++++--------------------------- 1 file changed, 17 insertions(+), 41 deletions(-)
@@ -324,50 +322,50 @@ static struct FileTypeInfo const fileTypeInfo[] = { /* XXX QEMU says there's no magic for dmg, * /usr/share/misc/magic lists double magic (both offsets * would have to match) but then disables that check. */ - 0, NULL, ".dmg", + 0, NULL, 0, -1, 0, {0}, -1, 0, 0, NULL, NULL, NULL },
Is it even worth keeping the dmg entry around? But deleting it (if appropriate) should be separate from this patch.
The internals currently expect that we have an entry for every image type supported in libvirt, so we need the dummy entry anyways.
Reviewed-by: Eric Blake <eblake@redhat.com>
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
We call virStorageFileSupportsBackingChainTraversal which already checks that the 'storageFileRead' callback is non-NULL, which in turn means that virStorageFileRead will not return -2. Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index 4d2e39246c..7aeeab0739 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -5003,15 +5003,8 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, goto cleanup; if ((headerLen = virStorageFileRead(src, 0, VIR_STORAGE_MAX_HEADER, - &buf)) < 0) { - if (headerLen == -2) - virReportError(VIR_ERR_INTERNAL_ERROR, - _("storage file reading is not supported for " - "storage type %s (protocol: %s)"), - virStorageTypeToString(src->type), - virStorageNetProtocolTypeToString(src->protocol)); + &buf)) < 0) goto cleanup; - } if (virStorageFileGetMetadataInternal(src, buf, headerLen, &backingFormat) < 0) -- 2.24.1
On 2/17/20 11:13 AM, Peter Krempa wrote:
We call virStorageFileSupportsBackingChainTraversal which already checks that the 'storageFileRead' callback is non-NULL, which in turn means that virStorageFileRead will not return -2.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-)
Concur that it was dead code. Reviewed-by: Eric Blake <eblake@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
Move the assignment to a place where we know that the backing store is present rather than having to check in the cleanup section. Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index 7aeeab0739..f8e4102588 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -5053,14 +5053,15 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, ret = 0; goto cleanup; } + + backingStore->id = depth; + src->backingStore = g_steal_pointer(&backingStore); } else { /* add terminator */ - if (!(backingStore = virStorageSourceNew())) + if (!(src->backingStore = virStorageSourceNew())) goto cleanup; } - src->backingStore = g_steal_pointer(&backingStore); - if (src->externalDataStoreRaw) { g_autoptr(virStorageSource) externalDataStore = NULL; @@ -5080,8 +5081,6 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, ret = 0; cleanup: - if (virStorageSourceHasBacking(src)) - src->backingStore->id = depth; virStorageFileDeinit(src); return ret; } -- 2.24.1
On 2/17/20 11:13 AM, Peter Krempa wrote:
Move the assignment to a place where we know that the backing store is present rather than having to check in the cleanup section.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
Reviewed-by: Eric Blake <eblake@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
The path can be NULL e.g. for NBD disks. Use NULLSTR to prevent use of NULL in %s. Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index f8e4102588..cf37744d6f 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -4973,7 +4973,7 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, g_autoptr(virStorageSource) backingStore = NULL; VIR_DEBUG("path=%s format=%d uid=%u gid=%u", - src->path, src->format, + NULLSTR(src->path), src->format, (unsigned int)uid, (unsigned int)gid); /* exit if we can't load information about the current image */ @@ -4995,7 +4995,7 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, if (virHashLookup(cycle, uniqueName)) { virReportError(VIR_ERR_INTERNAL_ERROR, _("backing store for %s (%s) is self-referential"), - src->path, uniqueName); + NULLSTR(src->path), uniqueName); goto cleanup; } -- 2.24.1
On 2/17/20 11:13 AM, Peter Krempa wrote:
The path can be NULL e.g. for NBD disks. Use NULLSTR to prevent use of NULL in %s.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index f8e4102588..cf37744d6f 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -4973,7 +4973,7 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, g_autoptr(virStorageSource) backingStore = NULL;
VIR_DEBUG("path=%s format=%d uid=%u gid=%u", - src->path, src->format, + NULLSTR(src->path), src->format, (unsigned int)uid, (unsigned int)gid);
Here, it matters in log output;
/* exit if we can't load information about the current image */ @@ -4995,7 +4995,7 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, if (virHashLookup(cycle, uniqueName)) { virReportError(VIR_ERR_INTERNAL_ERROR, _("backing store for %s (%s) is self-referential"), - src->path, uniqueName); + NULLSTR(src->path), uniqueName);
here, we're less likely to see the message. But being consistent is worthwhile. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
Replacing virHashLookup by virHashHasEntry allows to use NULL as the payload of the hash table rather than putting a fake '1' pointer into the table. Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index cf37744d6f..bb3fa65a14 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -4992,14 +4992,14 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, if (!(uniqueName = virStorageFileGetUniqueIdentifier(src))) goto cleanup; - if (virHashLookup(cycle, uniqueName)) { + if (virHashHasEntry(cycle, uniqueName)) { virReportError(VIR_ERR_INTERNAL_ERROR, _("backing store for %s (%s) is self-referential"), NULLSTR(src->path), uniqueName); goto cleanup; } - if (virHashAddEntry(cycle, uniqueName, (void *)1) < 0) + if (virHashAddEntry(cycle, uniqueName, NULL) < 0) goto cleanup; if ((headerLen = virStorageFileRead(src, 0, VIR_STORAGE_MAX_HEADER, -- 2.24.1
On 2/17/20 11:13 AM, Peter Krempa wrote:
Replacing virHashLookup by virHashHasEntry allows to use NULL as the
allows us to
payload of the hash table rather than putting a fake '1' pointer into the table.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
Reviewed-by: Eric Blake <eblake@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
Extract the code that directly deals with storage. This allows further simplification and clarification of virStorageFileGetMetadataRecurse. Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 71 ++++++++++++++++++++++++++------------- 1 file changed, 47 insertions(+), 24 deletions(-) diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index bb3fa65a14..1e21d44c67 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -4955,31 +4955,18 @@ virStorageFileReportBrokenChain(int errcode, } -/* Recursive workhorse for virStorageFileGetMetadata. */ static int -virStorageFileGetMetadataRecurse(virStorageSourcePtr src, - virStorageSourcePtr parent, - uid_t uid, gid_t gid, - bool report_broken, - virHashTablePtr cycle, - unsigned int depth) +virStorageFileGetMetadataRecurseReadHeader(virStorageSourcePtr src, + virStorageSourcePtr parent, + uid_t uid, + gid_t gid, + char **buf, + size_t *headerLen, + virHashTablePtr cycle) { int ret = -1; const char *uniqueName; - ssize_t headerLen; - int backingFormat; - int rv; - g_autofree char *buf = NULL; - g_autoptr(virStorageSource) backingStore = NULL; - - VIR_DEBUG("path=%s format=%d uid=%u gid=%u", - NULLSTR(src->path), src->format, - (unsigned int)uid, (unsigned int)gid); - - /* exit if we can't load information about the current image */ - rv = virStorageFileSupportsBackingChainTraversal(src); - if (rv <= 0) - return rv; + ssize_t len; if (virStorageFileInitAs(src, uid, gid) < 0) return -1; @@ -5002,10 +4989,47 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, if (virHashAddEntry(cycle, uniqueName, NULL) < 0) goto cleanup; - if ((headerLen = virStorageFileRead(src, 0, VIR_STORAGE_MAX_HEADER, - &buf)) < 0) + if ((len = virStorageFileRead(src, 0, VIR_STORAGE_MAX_HEADER, buf)) < 0) goto cleanup; + *headerLen = len; + ret = 0; + + cleanup: + virStorageFileDeinit(src); + return ret; +} + + +/* Recursive workhorse for virStorageFileGetMetadata. */ +static int +virStorageFileGetMetadataRecurse(virStorageSourcePtr src, + virStorageSourcePtr parent, + uid_t uid, gid_t gid, + bool report_broken, + virHashTablePtr cycle, + unsigned int depth) +{ + int ret = -1; + size_t headerLen; + int backingFormat; + int rv; + g_autofree char *buf = NULL; + g_autoptr(virStorageSource) backingStore = NULL; + + VIR_DEBUG("path=%s format=%d uid=%u gid=%u", + NULLSTR(src->path), src->format, + (unsigned int)uid, (unsigned int)gid); + + /* exit if we can't load information about the current image */ + rv = virStorageFileSupportsBackingChainTraversal(src); + if (rv <= 0) + return rv; + + if (virStorageFileGetMetadataRecurseReadHeader(src, parent, uid, gid, + &buf, &headerLen, cycle) < 0) + return -1; + if (virStorageFileGetMetadataInternal(src, buf, headerLen, &backingFormat) < 0) goto cleanup; @@ -5081,7 +5105,6 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, ret = 0; cleanup: - virStorageFileDeinit(src); return ret; } -- 2.24.1
On 2/17/20 11:13 AM, Peter Krempa wrote:
Extract the code that directly deals with storage. This allows further simplification and clarification of virStorageFileGetMetadataRecurse.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 71 ++++++++++++++++++++++++++------------- 1 file changed, 47 insertions(+), 24 deletions(-)
Reviewed-by: Eric Blake <eblake@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
There's nothing to clean up. Make it obvious what is returned. Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 50 +++++++++++++++------------------------ 1 file changed, 19 insertions(+), 31 deletions(-) diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index 1e21d44c67..b984204b93 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -5010,7 +5010,6 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, virHashTablePtr cycle, unsigned int depth) { - int ret = -1; size_t headerLen; int backingFormat; int rv; @@ -5030,19 +5029,16 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, &buf, &headerLen, cycle) < 0) return -1; - if (virStorageFileGetMetadataInternal(src, buf, headerLen, - &backingFormat) < 0) - goto cleanup; + if (virStorageFileGetMetadataInternal(src, buf, headerLen, &backingFormat) < 0) + return -1; if (src->backingStoreRaw) { if ((rv = virStorageSourceNewFromBacking(src, &backingStore)) < 0) - goto cleanup; + return -1; - if (rv == 1) { - /* the backing file would not be usable for VM usage */ - ret = 0; - goto cleanup; - } + /* the backing file would not be usable for VM usage */ + if (rv == 1) + return 0; backingStore->format = backingFormat; @@ -5065,17 +5061,14 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, if (backingStore->format == VIR_STORAGE_FILE_AUTO_SAFE) backingStore->format = VIR_STORAGE_FILE_AUTO; - if ((ret = virStorageFileGetMetadataRecurse(backingStore, parent, - uid, gid, - report_broken, - cycle, depth + 1)) < 0) { + if (virStorageFileGetMetadataRecurse(backingStore, parent, + uid, gid, + report_broken, + cycle, depth + 1) < 0) { if (report_broken) - goto cleanup; - - /* if we fail somewhere midway, just accept and return a - * broken chain */ - ret = 0; - goto cleanup; + return -1; + else + return 0; } backingStore->id = depth; @@ -5083,7 +5076,7 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, } else { /* add terminator */ if (!(src->backingStore = virStorageSourceNew())) - goto cleanup; + return -1; } if (src->externalDataStoreRaw) { @@ -5091,21 +5084,16 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, if ((rv = virStorageSourceNewFromExternalData(src, &externalDataStore)) < 0) - goto cleanup; + return -1; - if (rv == 1) { - /* the file would not be usable for VM usage */ - ret = 0; - goto cleanup; - } + /* the file would not be usable for VM usage */ + if (rv == 1) + return 0; src->externalDataStore = g_steal_pointer(&externalDataStore); } - ret = 0; - - cleanup: - return ret; + return 0; } -- 2.24.1
On 2/17/20 11:13 AM, Peter Krempa wrote:
There's nothing to clean up. Make it obvious what is returned.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 50 +++++++++++++++------------------------ 1 file changed, 19 insertions(+), 31 deletions(-)
Reviewed-by: Eric Blake <eblake@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
Allow format probing to work around lazy clients which did not specify their format in the overlay. Format probing will be allowed only, if we are able to probe the image, the probing result was successful and the probed image does not have any backing or data file. This relaxes the restrictions which were imposed in commit 3615e8b39bad in cases when we know that the image probing will not result in security issues or data corruption. We perform the image format detection and in the case that we were able to probe the format and the format does not specify a backing store (or doesn't support backing store) we can use this format. With pre-blockdev configurations this will restore the previous behaviour for the images mentioned above as qemu would probe the format anyways. It also improves error reporting compared to the old state as we now report that the backing chain will be broken in case when there is a backing file. In blockdev configurations this ensures that libvirt will not cause data corruption by ending the chain prematurely without notifying the user, but still allows the old semantics when the users forgot to specify the format. The price for this is that libvirt will need to keep the image format detector still current and working or replace it by invocation of qemu-img. Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 52 ++++++++++++++++++++++----------------- 1 file changed, 30 insertions(+), 22 deletions(-) diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index b984204b93..bbdf7be094 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -5010,6 +5010,7 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, virHashTablePtr cycle, unsigned int depth) { + virStorageFileFormat orig_format = src->format; size_t headerLen; int backingFormat; int rv; @@ -5020,10 +5021,17 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, NULLSTR(src->path), src->format, (unsigned int)uid, (unsigned int)gid); + if (src->format == VIR_STORAGE_FILE_AUTO_SAFE) + src->format = VIR_STORAGE_FILE_AUTO; + /* exit if we can't load information about the current image */ rv = virStorageFileSupportsBackingChainTraversal(src); - if (rv <= 0) + if (rv <= 0) { + if (orig_format == VIR_STORAGE_FILE_AUTO) + return -2; + return rv; + } if (virStorageFileGetMetadataRecurseReadHeader(src, parent, uid, gid, &buf, &headerLen, cycle) < 0) @@ -5032,6 +5040,18 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, if (virStorageFileGetMetadataInternal(src, buf, headerLen, &backingFormat) < 0) return -1; + /* If we probed the format we MUST ensure that nothing else than the current + * image (this includes both backing files and external data store) is + * considered for security labelling and/or recursion. */ + if (orig_format == VIR_STORAGE_FILE_AUTO) { + if (src->backingStoreRaw || src->externalDataStoreRaw) { + src->format = VIR_STORAGE_FILE_RAW; + VIR_FREE(src->backingStoreRaw); + VIR_FREE(src->externalDataStoreRaw); + return -2; + } + } + if (src->backingStoreRaw) { if ((rv = virStorageSourceNewFromBacking(src, &backingStore)) < 0) return -1; @@ -5042,33 +5062,21 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, backingStore->format = backingFormat; - if (backingStore->format == VIR_STORAGE_FILE_AUTO) { - /* Assuming the backing store to be raw can lead to failures. We do - * it only when we must not report an error to prevent losing VMs. - * Otherwise report an error. - */ - if (report_broken) { + if ((rv = virStorageFileGetMetadataRecurse(backingStore, parent, + uid, gid, + report_broken, + cycle, depth + 1)) < 0) { + if (!report_broken) + return 0; + + if (rv == -2) { virReportError(VIR_ERR_OPERATION_INVALID, _("format of backing image '%s' of image '%s' was not specified in the image metadata " "(See https://libvirt.org/kbase/backing_chains.html for troubleshooting)"), src->backingStoreRaw, NULLSTR(src->path)); - return -1; } - backingStore->format = VIR_STORAGE_FILE_RAW; - } - - if (backingStore->format == VIR_STORAGE_FILE_AUTO_SAFE) - backingStore->format = VIR_STORAGE_FILE_AUTO; - - if (virStorageFileGetMetadataRecurse(backingStore, parent, - uid, gid, - report_broken, - cycle, depth + 1) < 0) { - if (report_broken) - return -1; - else - return 0; + return -1; } backingStore->id = depth; -- 2.24.1
On 2/17/20 11:13 AM, Peter Krempa wrote:
Allow format probing to work around lazy clients which did not specify their format in the overlay. Format probing will be allowed only, if we
s/only, if/only if/
are able to probe the image, the probing result was successful and the probed image does not have any backing or data file.
This relaxes the restrictions which were imposed in commit 3615e8b39bad in cases when we know that the image probing will not result in security issues or data corruption.
It took me a few minutes of thinking about this. Scenario 1: base.raw <- wrap.qcow2 where wrap.qcow2 specifies backing of base.raw but not the format. If we probe, we can have a couple of outcomes: 1a: base.raw probes as raw (the probed image has no backing or data file), using it as raw is safe (it matches what wrap.qcow2 should have specified but didn't, and we aren't changing the data the guest would read nor are we opening unexpected files) 1b: base.raw probes as qcow2 (because of whatever the guest wrote there), using it as qcow2 is wrong - the guest will see corrupted data. What's more, if the probe sees it as qcow2 with backing file, and we open the backing file, it also has security implications. Scenario 2: base.qcow2 <- wrap.qcow2 where wrap.qcow2 specifies backing of base.qcow2 but not the format. If we probe, we will always have just one outcome: 2a: base.qcow2 probes as qcow2. Using it as qcow2 is correct, but if base.qcow2 has a further backing image, the backing chain is now dependent on a probe. Since 1b and 2a have the same probe result, but massively different data corruption and/or security concerns, it is NOT sufficient to claim that a probe was safe merely because "the probed image does not have any backing or data file". It is ONLY safe if the probe turns up raw. Any other probed format is inherently unsafe.
We perform the image format detection and in the case that we were able to probe the format and the format does not specify a backing store (or doesn't support backing store) we can use this format.
Wrong. The condition needs to be: If we probe the format, and the probe returns raw, then it is safe to use raw as the format.
With pre-blockdev configurations this will restore the previous behaviour for the images mentioned above as qemu would probe the format anyways. It also improves error reporting compared to the old state as we now report that the backing chain will be broken in case when there is a backing file.
Improved error reporting because the probe returned qcow2 that would have required us to chase a backing file is fine; but while blindly accepting a qcow2 probe result when there is no backing file might avoid the security issue of chasing a backing file under guest control, it does not solve the data corruption issue of interpreting data as qcow2 that should have been interpreted as raw.
In blockdev configurations this ensures that libvirt will not cause data corruption by ending the chain prematurely without notifying the user, but still allows the old semantics when the users forgot to specify the format.
The only time where it is safe to imply a forgotten format is if the probed format is still raw.
The price for this is that libvirt will need to keep the image format detector still current and working or replace it by invocation of qemu-img.
Maybe. Any format that qemu recognizes but libvirt does not risks a case where libvirt probes the image as raw but lets qemu re-probe the image and then qemu exposes different data. But as long as libvirt always passes explicit format to qemu (including explicit raw format of a backing file whose format was forgotten but probing said it was raw), then it doesn't matter what other formats libvirt can probe for. The only benefit for libvirt probing formats is then for better error messages for non-raw.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 52 ++++++++++++++++++++++----------------- 1 file changed, 30 insertions(+), 22 deletions(-)
diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index b984204b93..bbdf7be094 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -5010,6 +5010,7 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, virHashTablePtr cycle, unsigned int depth) { + virStorageFileFormat orig_format = src->format; size_t headerLen; int backingFormat; int rv; @@ -5020,10 +5021,17 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, NULLSTR(src->path), src->format, (unsigned int)uid, (unsigned int)gid);
+ if (src->format == VIR_STORAGE_FILE_AUTO_SAFE) + src->format = VIR_STORAGE_FILE_AUTO; + /* exit if we can't load information about the current image */ rv = virStorageFileSupportsBackingChainTraversal(src); - if (rv <= 0) + if (rv <= 0) { + if (orig_format == VIR_STORAGE_FILE_AUTO) + return -2; + return rv; + }
if (virStorageFileGetMetadataRecurseReadHeader(src, parent, uid, gid, &buf, &headerLen, cycle) < 0) @@ -5032,6 +5040,18 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src, if (virStorageFileGetMetadataInternal(src, buf, headerLen, &backingFormat) < 0) return -1;
+ /* If we probed the format we MUST ensure that nothing else than the current + * image (this includes both backing files and external data store) is + * considered for security labelling and/or recursion. */
Grammar: If we probed the format, we MUST ensure that nothing besides the current image (including both backing files and external data store) will be considered for security labelling and/or recursion.
+ if (orig_format == VIR_STORAGE_FILE_AUTO) { + if (src->backingStoreRaw || src->externalDataStoreRaw) { + src->format = VIR_STORAGE_FILE_RAW; + VIR_FREE(src->backingStoreRaw); + VIR_FREE(src->externalDataStoreRaw); + return -2; + } + } + if (src->backingStoreRaw) { if ((rv = virStorageSourceNewFromBacking(src, &backingStore)) < 0) return -1; @@ -5042,33 +5062,21 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src,
backingStore->format = backingFormat;
- if (backingStore->format == VIR_STORAGE_FILE_AUTO) { - /* Assuming the backing store to be raw can lead to failures. We do - * it only when we must not report an error to prevent losing VMs. - * Otherwise report an error. - */ - if (report_broken) { + if ((rv = virStorageFileGetMetadataRecurse(backingStore, parent, + uid, gid, + report_broken, + cycle, depth + 1)) < 0) { + if (!report_broken) + return 0; + + if (rv == -2) { virReportError(VIR_ERR_OPERATION_INVALID, _("format of backing image '%s' of image '%s' was not specified in the image metadata " "(See https://libvirt.org/kbase/backing_chains.html for troubleshooting)"), src->backingStoreRaw, NULLSTR(src->path));
I disagree with the logic here. What we really need is: If the backing format was not specified, we probe to see what is there. If the result of that probe is raw, it is safe to treat the image as raw. If the result is anything else, we must report an error stating that what we probed could not be trusted unless the user adds an explicit backing format (either confirming that our probe was correct, or with the correct format overriding what we mis-probed). -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
On Wed, Feb 19, 2020 at 10:21:00 -0600, Eric Blake wrote:
On 2/17/20 11:13 AM, Peter Krempa wrote:
Allow format probing to work around lazy clients which did not specify their format in the overlay. Format probing will be allowed only, if we
s/only, if/only if/
are able to probe the image, the probing result was successful and the probed image does not have any backing or data file.
This relaxes the restrictions which were imposed in commit 3615e8b39bad in cases when we know that the image probing will not result in security issues or data corruption.
It took me a few minutes of thinking about this.
Scenario 1:
base.raw <- wrap.qcow2
where wrap.qcow2 specifies backing of base.raw but not the format. If we probe, we can have a couple of outcomes:
1a: base.raw probes as raw (the probed image has no backing or data file), using it as raw is safe (it matches what wrap.qcow2 should have specified but didn't, and we aren't changing the data the guest would read nor are we opening unexpected files)
1b: base.raw probes as qcow2 (because of whatever the guest wrote there), using it as qcow2 is wrong - the guest will see corrupted data. What's more, if the probe sees it as qcow2 with backing file, and we open the backing file, it also has security implications.
We don't open the backing file in the proposed logic. That is specifically forbidden. Also in pre-blockdev configurations the same situation would happen as we allowed qemu to probe the backing file despite assuming the format to be raw. This was as we weren't able to tell qemu what the backing format is. This is fixed with -blockdev, so this scenario is exactly the same as it was before.
Scenario 2:
base.qcow2 <- wrap.qcow2
where wrap.qcow2 specifies backing of base.qcow2 but not the format. If we probe, we will always have just one outcome:
2a: base.qcow2 probes as qcow2. Using it as qcow2 is correct, but if base.qcow2 has a further backing image, the backing chain is now dependent on a probe.
Since 1b and 2a have the same probe result, but massively different data corruption and/or security concerns, it is NOT sufficient to claim that a probe was safe merely because "the probed image does not have any backing or data file". It is ONLY safe if the probe turns up raw. Any other probed format is inherently unsafe.
I disagree here. If the probe of 'base.qcow2' showed a backing file, we refuse startup right away. If it didn't show any backing file, we continue: 1) with old (pre-blockdev qemus) libvirt starts qemu with wrap.qcow2 as image. Qemu tries to open the backing file and probes it. Now if we've mis-detected that there is a backing file, we will depend on sVirt to save us. This scenario is how all of this was working until 2 months ago. It's because we've asumed that the format of 'base.qcow2' was raw, but started qemu. Since we didn't tell qemu what the format of 'base.qcow2' as it was impossible, we've relied on sVirt anyways. This is the same as it was before. 2) with new qemu, we do the same, but start qemu and specifically tell it that "the backing format is qcow2 and that the image has no backing file. That way qemu doesn't even attempt to open anythting. This means that this scenario fixes any deployment without selinux, while keeping old semantics around.
We perform the image format detection and in the case that we were able to probe the format and the format does not specify a backing store (or doesn't support backing store) we can use this format.
Wrong. The condition needs to be:
If we probe the format, and the probe returns raw, then it is safe to use raw as the format.
That doesn't solve anythign then. The idea of this series is to relax the restrictions we've imposed after introducing blockdev to return the main semantics back to what we've allowed in pre-blockdev configurations. Namely a user creates an overlay on top of single raw/qcow2 image and expects it to work. And it's not just random users, libguestfs and openstack also neglected to set the backing format.
With pre-blockdev configurations this will restore the previous behaviour for the images mentioned above as qemu would probe the format anyways. It also improves error reporting compared to the old state as we now report that the backing chain will be broken in case when there is a backing file.
Improved error reporting because the probe returned qcow2 that would have required us to chase a backing file is fine; but while blindly accepting a qcow2 probe result when there is no backing file might avoid the security issue of chasing a backing file under guest control, it does not solve the data corruption issue of interpreting data as qcow2 that should have been interpreted as raw.
Again, this same scenario would happen previously, where we allowed qemu to probe despite assuming the image to be raw, since we were unable to tell qemu otherwise.
In blockdev configurations this ensures that libvirt will not cause data corruption by ending the chain prematurely without notifying the user, but still allows the old semantics when the users forgot to specify the format.
The only time where it is safe to imply a forgotten format is if the probed format is still raw.
The price for this is that libvirt will need to keep the image format detector still current and working or replace it by invocation of qemu-img.
Maybe. Any format that qemu recognizes but libvirt does not risks a case where libvirt probes the image as raw but lets qemu re-probe the image and
That doesn't happen with blockdev. We dont' let qemu probe.
then qemu exposes different data. But as long as libvirt always passes explicit format to qemu (including explicit raw format of a backing file whose format was forgotten but probing said it was raw), then it doesn't matter what other formats libvirt can probe for. The only benefit for libvirt probing formats is then for better error messages for non-raw.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> --- src/util/virstoragefile.c | 52 ++++++++++++++++++++++----------------- 1 file changed, 30 insertions(+), 22 deletions(-)
[....]
- if (backingStore->format == VIR_STORAGE_FILE_AUTO) { - /* Assuming the backing store to be raw can lead to failures. We do - * it only when we must not report an error to prevent losing VMs. - * Otherwise report an error. - */ - if (report_broken) { + if ((rv = virStorageFileGetMetadataRecurse(backingStore, parent, + uid, gid, + report_broken, + cycle, depth + 1)) < 0) { + if (!report_broken) + return 0; + + if (rv == -2) { virReportError(VIR_ERR_OPERATION_INVALID, _("format of backing image '%s' of image '%s' was not specified in the image metadata " "(See https://libvirt.org/kbase/backing_chains.html for troubleshooting)"), src->backingStoreRaw, NULLSTR(src->path));
I disagree with the logic here. What we really need is:
If the backing format was not specified, we probe to see what is there. If the result of that probe is raw, it is safe to treat the image as raw. If the result is anything else, we must report an error stating that what we probed could not be trusted unless the user adds an explicit backing format (either confirming that our probe was correct, or with the correct format overriding what we mis-probed).
As noted above, using this logic would be pointless. We are better off just reporting the error always if we also don't allow qcow2 without backing file to be used as it was previously used.
On Wed, Feb 19, 2020 at 17:40:34 +0100, Peter Krempa wrote:
On Wed, Feb 19, 2020 at 10:21:00 -0600, Eric Blake wrote:
On 2/17/20 11:13 AM, Peter Krempa wrote:
[...]
With pre-blockdev configurations this will restore the previous behaviour for the images mentioned above as qemu would probe the format anyways. It also improves error reporting compared to the old state as we now report that the backing chain will be broken in case when there is a backing file.
Improved error reporting because the probe returned qcow2 that would have required us to chase a backing file is fine; but while blindly accepting a qcow2 probe result when there is no backing file might avoid the security issue of chasing a backing file under guest control, it does not solve the
As said, we allowed that before and it's fixed with blockdev.
data corruption issue of interpreting data as qcow2 that should have been interpreted as raw.
Also don't forget that there's the issue of mis-detecting qcow2 as raw. That results in worse as the other way around as qemu will object if an image is not really qcow2 if being told that it is. If we declare it as raw, the guests starts and sees garbage. [1] This means that if we don't want to allow probing of 'qcow2 without backing' as working in the above scenario, we are better of just always requiring users to pass the format in the overlay as It's not worth just doing it for 'raw' images with all the potential drawbacks of mis-detecting qcow2 as raw. [1] That's what happened when blockdev was introduced and it resulted in the logic which I'm wanting to relax. We didn't refuse it before.
On 2/19/20 10:40 AM, Peter Krempa wrote:
1b: base.raw probes as qcow2 (because of whatever the guest wrote there), using it as qcow2 is wrong - the guest will see corrupted data. What's more, if the probe sees it as qcow2 with backing file, and we open the backing file, it also has security implications.
We don't open the backing file in the proposed logic. That is specifically forbidden.
I agree that you contained the security risk by not following any file names mentioned in based.raw when interpreted as qcow2, but that does not mean you contained the data corruption risk.
Also in pre-blockdev configurations the same situation would happen as we allowed qemu to probe the backing file despite assuming the format to be raw. This was as we weren't able to tell qemu what the backing format is. This is fixed with -blockdev, so this scenario is exactly the same as it was before.
We assumed it to be raw, the question is whether qemu also assumed it to be raw, or qemu assumed it to be qcow2. If qemu assumed it to be qcow2, sVirt may have saved us from the assumption going haywire and opening forbidden files, but it did NOT save the guest from seeing corrupted data. If qemu assumed it to be raw, then all that was missing pre-blockdev was a way for us to tell qemu its assumptions were correct.
Scenario 2:
base.qcow2 <- wrap.qcow2
where wrap.qcow2 specifies backing of base.qcow2 but not the format. If we probe, we will always have just one outcome:
2a: base.qcow2 probes as qcow2. Using it as qcow2 is correct, but if base.qcow2 has a further backing image, the backing chain is now dependent on a probe.
Since 1b and 2a have the same probe result, but massively different data corruption and/or security concerns, it is NOT sufficient to claim that a probe was safe merely because "the probed image does not have any backing or data file". It is ONLY safe if the probe turns up raw. Any other probed format is inherently unsafe.
I disagree here. If the probe of 'base.qcow2' showed a backing file, we refuse startup right away. If it didn't show any backing file, we continue:
1) with old (pre-blockdev qemus) libvirt starts qemu with wrap.qcow2 as image. Qemu tries to open the backing file and probes it. Now if we've mis-detected that there is a backing file, we will depend on sVirt to save us. This scenario is how all of this was working until 2 months ago. It's because we've asumed that the format of 'base.qcow2' was raw, but started qemu. Since we didn't tell qemu what the format of 'base.qcow2' as it was impossible, we've relied on sVirt anyways.
This is the same as it was before.
So you're arguing that because qemu probes and treats the file as qcow2, even though we had assumed raw, but that the data actually was qcow2 (so the guest did not see data corruption), that we want to continue this practice by explicitly telling qemu that it is qcow2. Then this all boils down to "what does qemu do when it probes an image that does not result in raw". If qemu trusted the probe results anyway, then data corruption was already possible, but once the data corruption happens, the guest can no longer reverse the corruption nor cause further security damage (once qemu treats a previously-raw image as qcow2, the guest can no longer rewrite the qcow2 metadata). If qemu failed to use the image because it treated the image as raw, then libvirt's decision to tell qemu that the image is qcow2 will CAUSE data corruption. I recall that older qemu did blindly trust the probe results, but that there was discussion on the qemu list about patching things to warn about probes that resulted in anything other than raw. But I could not quickly find mailing list discussions or specific patches that mention what actually happens; the closest I got was: commit e4c8f2925d22584b2008aadea5c70e1e05c2a522 Author: Daniel P. Berrangé <berrange@redhat.com> Date: Tue Nov 20 17:56:46 2018 +0000 iotests: fix nbd test 233 to work correctly with raw images The first qemu-io command must honour the $IMGFMT that is set rather than hardcoding qcow2. The qemu-nbd commands should also set $IMGFMT to avoid the insecure format probe warning.
2) with new qemu, we do the same, but start qemu and specifically tell it that "the backing format is qcow2 and that the image has no backing file. That way qemu doesn't even attempt to open anythting. This means that this scenario fixes any deployment without selinux, while keeping old semantics around.
If you tell qemu that something is qcow2, but qemu has ever in the past treated that file as raw, then you are forcing data corruption on the guest, even if you avoid a security issue of chasing further backing files from treating that image as qcow2.
We perform the image format detection and in the case that we were able to probe the format and the format does not specify a backing store (or doesn't support backing store) we can use this format.
Wrong. The condition needs to be:
If we probe the format, and the probe returns raw, then it is safe to use raw as the format.
That doesn't solve anythign then. The idea of this series is to relax the restrictions we've imposed after introducing blockdev to return the main semantics back to what we've allowed in pre-blockdev configurations.
The only way I see that might be safe to relax restrictions is if the filename heuristics give us a clue as to the user's intent. Data corruption is bad enough that we should never be the cause of it. A user with a broken setup deserves a decent error message that their setup is broken, and how to fix it (even so much as "we detected qcow2, but weren't sure if you might have had a raw file instead, so do this to tell us which one you meant"), but blindly picking one always creates a corner case where our choice is wrong.
Namely a user creates an overlay on top of single raw/qcow2 image and expects it to work. And it's not just random users, libguestfs and openstack also neglected to set the backing format.
Yes, and they are getting patched. Belatedly, but better late than never.
The price for this is that libvirt will need to keep the image format detector still current and working or replace it by invocation of qemu-img.
Maybe. Any format that qemu recognizes but libvirt does not risks a case where libvirt probes the image as raw but lets qemu re-probe the image and
That doesn't happen with blockdev. We dont' let qemu probe.
We are just shifting the burden on who causes the data corruption when a probe goes wrong - it used to be qemu, now it is libvirt.
I disagree with the logic here. What we really need is:
If the backing format was not specified, we probe to see what is there. If the result of that probe is raw, it is safe to treat the image as raw. If the result is anything else, we must report an error stating that what we probed could not be trusted unless the user adds an explicit backing format (either confirming that our probe was correct, or with the correct format overriding what we mis-probed).
As noted above, using this logic would be pointless. We are better off just reporting the error always if we also don't allow qcow2 without backing file to be used as it was previously used.
Then report the error always. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
On Wed, Feb 19, 2020 at 11:07:09 -0600, Eric Blake wrote:
On 2/19/20 10:40 AM, Peter Krempa wrote:
[....]
Namely a user creates an overlay on top of single raw/qcow2 image and expects it to work. And it's not just random users, libguestfs and openstack also neglected to set the backing format.
Yes, and they are getting patched. Belatedly, but better late than never.
In that case, qemu-img should also be fixed to forbid 'create' without -F. Otherwise it's hard to argue that it's a wrong thing to do.
The price for this is that libvirt will need to keep the image format detector still current and working or replace it by invocation of qemu-img.
Maybe. Any format that qemu recognizes but libvirt does not risks a case where libvirt probes the image as raw but lets qemu re-probe the image and
That doesn't happen with blockdev. We dont' let qemu probe.
We are just shifting the burden on who causes the data corruption when a probe goes wrong - it used to be qemu, now it is libvirt.
I disagree with the logic here. What we really need is:
If the backing format was not specified, we probe to see what is there. If the result of that probe is raw, it is safe to treat the image as raw. If the result is anything else, we must report an error stating that what we probed could not be trusted unless the user adds an explicit backing format (either confirming that our probe was correct, or with the correct format overriding what we mis-probed).
As noted above, using this logic would be pointless. We are better off just reporting the error always if we also don't allow qcow2 without backing file to be used as it was previously used.
Then report the error always.
Well that's what we do right now. It seems kind of tempting to call this a right thing but let me summarize the semantics: - The "true" detection cases are not problematic - advantage is that existing (arguably suboptimal) configurations will keep working if we detect - For the "false" detection cases: - misdetection does not breach security (given that sVirt is used) - data corruption can occur if libvirt detects something else than qemu - this is true both directions (qcow2->raw, raw->qcow2) and the tradeoff: 1) If we allow detection, we trade compatibility for the (small) possibility of having to deal with corruption. 2) If we disallow detection we trade regression of behaviour for data corruption not being our problem. I started this trhead because I feel that the value of 1) is more than 2). Especially short term since qemu-img's default behaviour is allowing creation of images which would break with libvirt and the fact that we've tolerated the wrong behaviour for years. Additionally I think that we could just get rid of the copy of the image detection copy in libvirt and replace it by invocation of qemu-img. That way we could avoid any discrepancies in the detection process in the first place.
[adding qemu] On 2/19/20 12:57 PM, Peter Krempa wrote:
Namely a user creates an overlay on top of single raw/qcow2 image and expects it to work. And it's not just random users, libguestfs and openstack also neglected to set the backing format.
Yes, and they are getting patched. Belatedly, but better late than never.
In that case, qemu-img should also be fixed to forbid 'create' without -F. Otherwise it's hard to argue that it's a wrong thing to do.
Allowing -b without -F when the backing file probes as raw is safe, but yes, I agree qemu-img create should start a deprecation period of warning if -F is omitted, and turn it into a hard error when enough time elapses.
The price for this is that libvirt will need to keep the image format detector still current and working or replace it by invocation of qemu-img.
Maybe. Any format that qemu recognizes but libvirt does not risks a case where libvirt probes the image as raw but lets qemu re-probe the image and
That doesn't happen with blockdev. We dont' let qemu probe.
We are just shifting the burden on who causes the data corruption when a probe goes wrong - it used to be qemu, now it is libvirt.
I disagree with the logic here. What we really need is:
If the backing format was not specified, we probe to see what is there. If the result of that probe is raw, it is safe to treat the image as raw. If the result is anything else, we must report an error stating that what we probed could not be trusted unless the user adds an explicit backing format (either confirming that our probe was correct, or with the correct format overriding what we mis-probed).
As noted above, using this logic would be pointless. We are better off just reporting the error always if we also don't allow qcow2 without backing file to be used as it was previously used.
Then report the error always.
Well that's what we do right now. It seems kind of tempting to call this a right thing but let me summarize the semantics:
- The "true" detection cases are not problematic - advantage is that existing (arguably suboptimal) configurations will keep working if we detect - For the "false" detection cases: - misdetection does not breach security (given that sVirt is used) - data corruption can occur if libvirt detects something else than qemu - this is true both directions (qcow2->raw, raw->qcow2)
and the tradeoff:
1) If we allow detection, we trade compatibility for the (small) possibility of having to deal with corruption.
2) If we disallow detection we trade regression of behaviour for data corruption not being our problem.
I started this trhead because I feel that the value of 1) is more than 2). Especially short term since qemu-img's default behaviour is allowing creation of images which would break with libvirt and the fact that we've tolerated the wrong behaviour for years.
Additionally I think that we could just get rid of the copy of the image detection copy in libvirt and replace it by invocation of qemu-img. That way we could avoid any discrepancies in the detection process in the first place.
Now there's an interesting thought. Since data corruption occurs when there is disagreement about which mode to use, getting libvirt out of the probing business by deferring all decisions to qemu-img info is a smart move - if qemu says an image probes as qcow2 (in an environment where probing is safe), then libvirt passing an explicit qcow2 to qemu for guest usage (in an environment where probing is not safe) will at least see the same guest-visible data. Less code to maintain in libvirt, and no chance for a mismatch between the two projects on which format a probe should result in. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
On Wed, Feb 19, 2020 at 13:12:53 -0600, Eric Blake wrote:
[adding qemu]
Adding Daniel as he objected to qemu-img.
On 2/19/20 12:57 PM, Peter Krempa wrote:
[...]
Additionally I think that we could just get rid of the copy of the image detection copy in libvirt and replace it by invocation of qemu-img. That way we could avoid any discrepancies in the detection process in the first place.
Now there's an interesting thought. Since data corruption occurs when there is disagreement about which mode to use, getting libvirt out of the probing business by deferring all decisions to qemu-img info is a smart move - if qemu says an image probes as qcow2 (in an environment where probing is safe), then libvirt passing an explicit qcow2 to qemu for guest usage (in an environment where probing is not safe) will at least see the same guest-visible data. Less code to maintain in libvirt, and no chance for a mismatch between the two projects on which format a probe should result in.
I raised the use of qemu-img to Daniel and he disagreed with use of qemu-img in libvirt for doing the probing on multiple reasons: - qemu-img instantiates many data structures relevant to the format so it has a huge attack surface - performance of spawning extra processes would be way worse While at least from the point of view of VM startup both can be challenged this adds a complete new orthogonal dimension to the problem I'm attempting to fix. I'll reiterate the historical state of the problem because I think it's important: Pre-blockdev: - we internally assumed that if the image format of an backing image was not present in the overlay it is 'raw' - this influenced security labelling but not actually how qemu viewed or probed the file. If it was qcow2 probed as qcow2 qemu opened it as qcow2 possibly even including the backing file if selinux or other mechanism didn't prevent it. post-blockdev: - the assumption of 'raw' would now be expressed into the qemu configuration. This assumption turned into data corruption since we no longer allowed qemu to probe the format and forced it as raw. - fix was to always require the format to be recorded in the overlay - this made users unhappy who neglected to record the format into the overlay when creating it manually Now since qemu didn't discourage the creation of overlays without format there still are many users which will inevitably hit this problem when used with libvirt. My proposal tries to mitigate the regressions in behaviour in the valid and secure use cases. (If the image whose format we detect doesn't have a backing image) This comes at a trade-off though. As Eric pointed out, if the format probed by libvirt's internal code disagrees with qemu's format we are getting into the image corruption region. As a mitigation to the above I suggested using qemu-img to probe but that's a complex change and as mentioned above not really welcome upstream. Now this adds an interresting dimension to this problem. If libvirt forces the users to specify the image format, and the users don't know it they will probe. So we are basically making this a problem of somebody else. [2] As you can see in that patch, it uses 'qemu-img' anyways and also additionally actually allows the chain to continue deeper! [3] A partial relief to the image detection problem is that qemu would refuse to start if an non-qcow2 image is used in qcow2, thus we really only run into problems if qcow2 is mis-detected as raw. This boils down to whether we want to accept some possibility of image corruption in trade for avoiding regression of behaviour in the secure cases as well as management apps and users not having to re-invent when probing an image is actually safe. Finally I think we should either decide to fix it in this release, or stick with the error message forever. Fixing it later will not make much sense as many users already fixed their scripts and we'd just add back the trade-off of possible image corruption. Peter [1] If e.g. the security subsystem of the host didn't forbid the use of the backing file such a qcow2 qemu would happily open it. [2] https://www.redhat.com/archives/libguestfs/2020-February/msg00013.html [3] As implemented in [2] the backing image is not checked whether it has a backing file or not but the format is probed, which way result into accessing the backing chain of the probed image. Prior to this detection, it would be prevented by sVirt or alternatively also by libvit itself in -blockdev mode when this patch would be accepted.
On Mon, Feb 24, 2020 at 02:34:16PM +0100, Peter Krempa wrote:
On Wed, Feb 19, 2020 at 13:12:53 -0600, Eric Blake wrote:
[adding qemu]
Adding Daniel as he objected to qemu-img.
On 2/19/20 12:57 PM, Peter Krempa wrote:
[...]
Additionally I think that we could just get rid of the copy of the image detection copy in libvirt and replace it by invocation of qemu-img. That way we could avoid any discrepancies in the detection process in the first place.
Now there's an interesting thought. Since data corruption occurs when there is disagreement about which mode to use, getting libvirt out of the probing business by deferring all decisions to qemu-img info is a smart move - if qemu says an image probes as qcow2 (in an environment where probing is safe), then libvirt passing an explicit qcow2 to qemu for guest usage (in an environment where probing is not safe) will at least see the same guest-visible data. Less code to maintain in libvirt, and no chance for a mismatch between the two projects on which format a probe should result in.
I raised the use of qemu-img to Daniel and he disagreed with use of qemu-img in libvirt for doing the probing on multiple reasons: - qemu-img instantiates many data structures relevant to the format so it has a huge attack surface
This was the most critical reason why we have this code in libvirt in the first place. NB, we need to be sure we are comparing the same things between libvirt and QEMU when we discuss "probing". What we're talking about by probing in libvirt context is - Detect the image format - Detect the image virtual size - Detect the image physical size - Detect the image backing store location - Detect the image backing store format - Detect the image encryption usage In QEMU 'format probing' (as impl by bdrv_probe in QEMU's block layer) only covers the very first point, 'detect the image format'. All the other information can only be acquired by opening the image (bdrv_open in QEMU's block layer). The issue is that bdrv_open does waaaaaay more than we desire here, because it is serving the broader purpose of allowing QEMU to actually use the image. qcow2 is probably the worst case example, as it has to parse the image and setup data structures for l1, l2 tables, refcount tables, snapshots, and initialize the encryption layer if present. It is known that this code is vulnerable to maliciously created qcow2 images. This resulted in OpenStack being vulnerable to CVE-2015-5162 https://bugs.launchpad.net/ossa/+bug/1449062 It isn't possible to do anything to avoid this risk if you are invoking qemu-img on untrustworthy images. The best you can do is to mitigate the effects by placing memory/CPU ulimits on the qemu-img process. Determining these limits then introduces a new problem, as you have to pick a limit which is low enough to avoid DoS, while large enough to allow all valid usage. Since mitigating CVE-2015-5162 OpenStack has faced this problem with users reporting that the limits it set were breaking valid usage, as so had to increase the limits, which increases the DoS impact. Then there's also the pain that OSP suffered when QEMU introduced mandatory locking which broke all existing usage of 'qemu-img info' when a VM was running. Of course when you launch QEMU later, it is susceptible to the DoS in the system emulator, but this is mitigated by fact that upfront probing is going to reject some malicious images. If some bad images do get past, then it will be dealt with by the mgmt apps normal monitoring of a running VM resource usage and/or cgroups limits. The libvirt probing code is designed to do the minimal work needed to get the information we require. Of course there may be bugs in libvirt's code, but it is much more straightforward for us to analyse & understand risks, as most of the problematic code that QEMU has simply doesn't exist in libvirt.
- performance of spawning extra processes would be way worse
Yes, this was the second motivation for having this code in libvirt originally. The QEMU VM startup case wasn't the target, but rather storage pools code. When we start a storage pool with 100's of images, the time to spawn 100's of instances of qemu-img adds up very quickly. Even if qemu-img had exactly the same minimalist code as libvirt's current probing logic it would still be worse. The overhead of process startup vs the time spent probing the image is a poor ratio, such that process startup/exec time dominates. The third reason why libvirt has this code is because historically the error reporting from qemu-img has been quite unhelpful - many errors just end up being a generic EINVAL error message. Things have improved over time, but error reporting is always a challenge when spawning external commands to do work. The fourth reason why libvirt has this image file detection code is that it is used by non-QEMU drivers in libvirt, mostly notably the storage pool driver, and we didn't wish to force people to install qemu-img on hosts which were not running the QEMU virt driver. I don't think this reason is especially a technical show stopper, since these days all distros allow you to install qemu-img, without pulling in the rest of QEMU. In fact the storage pool driver RPM depends on qemu-img explicitly since we dropped support for the Xen tools for image creation a while ago. There is scope for something to replace the current libvirt probing code, but spawning 'qemu-img info' is certainly not that something. Libvirt (and apps above libvirt in general) would really benefit from having a library that they can use for readonly querying of information about disk images. Of course that library can't just spawn qemu-img otherwise that defeats the point of using a library. Unfortunately QEMU's block layer can't practically serve this role because its GPLv2-only licensing is too restrictive for some apps needs. It would have to be something conceptually similar in complexity to what libvirt's current probing code does, so that we can have good confidence in its behaviour in the face of malicious input.
I'll reiterate the historical state of the problem because I think it's important:
Pre-blockdev: - we internally assumed that if the image format of an backing image was not present in the overlay it is 'raw' - this influenced security labelling but not actually how qemu viewed or probed the file. If it was qcow2 probed as qcow2 qemu opened it as qcow2 possibly even including the backing file if selinux or other mechanism didn't prevent it.
post-blockdev: - the assumption of 'raw' would now be expressed into the qemu configuration. This assumption turned into data corruption since we no longer allowed qemu to probe the format and forced it as raw. - fix was to always require the format to be recorded in the overlay - this made users unhappy who neglected to record the format into the overlay when creating it manually
So the key problem we have is that with -blockdev we are always explicitly telling QEMU what the backing file is for every image. Can we fix this to have the exact same behaviour as before by *not* telling QEMU anything about the backing file when using -blockdev, if there is no well defined backing format present. ie, use -blockdev, but let QEMU probe just as it did in non-blockdev days. Would there be any downsides to this that did not already exist in the non-blockdev days ? I don't think we can solve the regressions in behaviour of backing files by doing probing of the backing files in libvirt, because that only works for the case where libvirt can actually open the file. ie a local file on disk. We don't have logic for opening backing files on RBD, GlusterFS, iSCSI, HTTP, SSH, etc, and nor do we want todo that. So to me it looks like the only viable option is to not specify the backing file info to QEMU at all.
Now this adds an interresting dimension to this problem. If libvirt forces the users to specify the image format, and the users don't know it they will probe. So we are basically making this a problem of somebody else. [2] As you can see in that patch, it uses 'qemu-img' anyways and also additionally actually allows the chain to continue deeper! [3]
Yeah, this is a really bad situation given the difficulty in safely using qemu-img, without also breaking valid usage. We don't want to push this off to apps
This boils down to whether we want to accept some possibility of image corruption in trade for avoiding regression of behaviour in the secure cases as well as management apps and users not having to re-invent when probing an image is actually safe.
I feel like the risk of image corruption is pretty minor. Our probing handles all normal cases the same way as QEMU and newly introduced image formats are rare.
Finally I think we should either decide to fix it in this release, or stick with the error message forever. Fixing it later will not make much sense as many users already fixed their scripts and we'd just add back the trade-off of possible image corruption.
Peter
[1] If e.g. the security subsystem of the host didn't forbid the use of the backing file such a qcow2 qemu would happily open it.
[2] https://www.redhat.com/archives/libguestfs/2020-February/msg00013.html
[3] As implemented in [2] the backing image is not checked whether it has a backing file or not but the format is probed, which way result into accessing the backing chain of the probed image.
Prior to this detection, it would be prevented by sVirt or alternatively also by libvit itself in -blockdev mode when this patch would be accepted.
Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On Mon, Feb 24, 2020 at 14:24:15 +0000, Daniel Berrange wrote:
On Mon, Feb 24, 2020 at 02:34:16PM +0100, Peter Krempa wrote:
On Wed, Feb 19, 2020 at 13:12:53 -0600, Eric Blake wrote:
[...]
I'll reiterate the historical state of the problem because I think it's important:
Pre-blockdev: - we internally assumed that if the image format of an backing image was not present in the overlay it is 'raw' - this influenced security labelling but not actually how qemu viewed or probed the file. If it was qcow2 probed as qcow2 qemu opened it as qcow2 possibly even including the backing file if selinux or other mechanism didn't prevent it.
post-blockdev: - the assumption of 'raw' would now be expressed into the qemu configuration. This assumption turned into data corruption since we no longer allowed qemu to probe the format and forced it as raw. - fix was to always require the format to be recorded in the overlay - this made users unhappy who neglected to record the format into the overlay when creating it manually
So the key problem we have is that with -blockdev we are always explicitly telling QEMU what the backing file is for every image.
Can we fix this to have the exact same behaviour as before by *not* telling QEMU anything about the backing file when using -blockdev, if there is no well defined backing format present. ie, use -blockdev, but let QEMU probe just as it did in non-blockdev days.
Would there be any downsides to this that did not already exist in the non-blockdev days ?
We can, but the price is that: 1) we won't allow blockjobs and anything blockdev-related because node name would be out of our control. This was possible in pre-blockdev era. 2) we will lose control of actually telling qemu to NOT open the backing file in that case. Distros using only unix permission still have arbitrary file access under permissions of the qemu process. 3) weird special-case code, because we need to keep some metadata about the image to do security labelling
I don't think we can solve the regressions in behaviour of backing files by doing probing of the backing files in libvirt, because that only works for the case where libvirt can actually open the file. ie a local file on disk. We don't have logic for opening backing files on RBD, GlusterFS, iSCSI, HTTP, SSH, etc, and nor do we want todo that.
Now we are back in the teritory where we actually do match what would happen with previously. We don't specify these on the command line with ehaviour matching what's described above, with the caveats as above. I kept this behaviour because we couldn't do better. This is in place even now if the last introspectable image has valid format specified. We can reconsider how to approach this but ideally separately.
So to me it looks like the only viable option is to not specify the backing file info to QEMU at all.
Now this adds an interresting dimension to this problem. If libvirt forces the users to specify the image format, and the users don't know it they will probe. So we are basically making this a problem of somebody else. [2] As you can see in that patch, it uses 'qemu-img' anyways and also additionally actually allows the chain to continue deeper! [3]
Yeah, this is a really bad situation given the difficulty in safely using qemu-img, without also breaking valid usage.
We don't want to push this off to apps
This boils down to whether we want to accept some possibility of image corruption in trade for avoiding regression of behaviour in the secure cases as well as management apps and users not having to re-invent when probing an image is actually safe.
I feel like the risk of image corruption is pretty minor. Our probing handles all normal cases the same way as QEMU and newly introduced image formats are rare.
Well, in this case I'm actually for re-considering the original patch discussed here. It uses image-format-probing code from libvirt, to allow the most common cases which were forbidden in a safe way. This means that as long as we can probe the image and the probed image does not have a backing file we allow the startup. It restores previous behaviour for valid cases including blockjobs, correctly revokes invalid cases (existing chain after image wihtout format, images impossible to introspect), is limited to the backing store walking code so can be contained and the price is doing the image format detection using libvirt's code.
On Mon, Feb 24, 2020 at 06:10:46PM +0100, Peter Krempa wrote:
On Mon, Feb 24, 2020 at 14:24:15 +0000, Daniel Berrange wrote:
On Mon, Feb 24, 2020 at 02:34:16PM +0100, Peter Krempa wrote:
On Wed, Feb 19, 2020 at 13:12:53 -0600, Eric Blake wrote:
[...]
I'll reiterate the historical state of the problem because I think it's important:
Pre-blockdev: - we internally assumed that if the image format of an backing image was not present in the overlay it is 'raw' - this influenced security labelling but not actually how qemu viewed or probed the file. If it was qcow2 probed as qcow2 qemu opened it as qcow2 possibly even including the backing file if selinux or other mechanism didn't prevent it.
post-blockdev: - the assumption of 'raw' would now be expressed into the qemu configuration. This assumption turned into data corruption since we no longer allowed qemu to probe the format and forced it as raw. - fix was to always require the format to be recorded in the overlay - this made users unhappy who neglected to record the format into the overlay when creating it manually
So the key problem we have is that with -blockdev we are always explicitly telling QEMU what the backing file is for every image.
Can we fix this to have the exact same behaviour as before by *not* telling QEMU anything about the backing file when using -blockdev, if there is no well defined backing format present. ie, use -blockdev, but let QEMU probe just as it did in non-blockdev days.
Would there be any downsides to this that did not already exist in the non-blockdev days ?
We can, but the price is that: 1) we won't allow blockjobs and anything blockdev-related because node name would be out of our control. This was possible in pre-blockdev era.
Ok, that's not viable then. We can't switch one regression for a different regression.
2) we will lose control of actually telling qemu to NOT open the backing file in that case. Distros using only unix permission still have arbitrary file access under permissions of the qemu process.
True, but that is at least historically expected behaviour, which can be fixed by setting <backingfile/> in the XML file IIUC.
3) weird special-case code, because we need to keep some metadata about the image to do security labelling
I don't think we can solve the regressions in behaviour of backing files by doing probing of the backing files in libvirt, because that only works for the case where libvirt can actually open the file. ie a local file on disk. We don't have logic for opening backing files on RBD, GlusterFS, iSCSI, HTTP, SSH, etc, and nor do we want todo that.
Now we are back in the teritory where we actually do match what would happen with previously. We don't specify these on the command line with ehaviour matching what's described above, with the caveats as above.
I kept this behaviour because we couldn't do better. This is in place even now if the last introspectable image has valid format specified.
We can reconsider how to approach this but ideally separately.
I'm a little lost as to exactly which scenarios are broken, and which we're fixing. 1. file:top.qcow2 -> file:base.raw 2. file:top.qcow2 -> file:base.qcow2 3. file:top.qcow2 -> file:middle.qcow2 -> file:base.raw 4. file:top.qcow2 -> file:middle.qcow2 -> file:base.qcow2 IIUC, (1) is working before and now, (2) is working before but broken now, and (3) and (4) were broken before and now. So (2) is the only one we /must/ to fix Am I right that by doing probing in libvirt as per this patch, as well as fixing (2) though, we'll accidentally fix (3) and (4) even though they were always broken before ? This all talks about qcow2 images on the file: protocol driver. What is the situation for, say, the iscsi: protocol driver 1. iscsi:top.qcow2 -> iscsi:base.raw 2. iscsi:top.qcow2 -> iscsi:base.qcow2 3. iscsi:top.qcow2 -> iscsi:middle.qcow2 -> iscsi:base.raw 4. iscsi:top.qcow2 -> iscsi:middle.qcow2 -> iscsi:base.qcow2 What was the behaviour of this in the pre-blockdev days and vs current git master ? Is it the same with (1) is working before and now, (2) is working before but broken now, and (3) and (4) were broken before and now. I'm assuming the libvirt probing cannot fix any case other than file: protocol, or host-device: protocol, since we're unable to open any other type of storage.
This boils down to whether we want to accept some possibility of image corruption in trade for avoiding regression of behaviour in the secure cases as well as management apps and users not having to re-invent when probing an image is actually safe.
I feel like the risk of image corruption is pretty minor. Our probing handles all normal cases the same way as QEMU and newly introduced image formats are rare.
Well, in this case I'm actually for re-considering the original patch discussed here. It uses image-format-probing code from libvirt, to allow the most common cases which were forbidden in a safe way. This means that as long as we can probe the image and the probed image does not have a backing file we allow the startup.
It restores previous behaviour for valid cases including blockjobs, correctly revokes invalid cases (existing chain after image wihtout format, images impossible to introspect), is limited to the backing store walking code so can be contained and the price is doing the image format detection using libvirt's code.
Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On Tue, Feb 25, 2020 at 12:50:21 +0000, Daniel Berrange wrote:
On Mon, Feb 24, 2020 at 06:10:46PM +0100, Peter Krempa wrote:
On Mon, Feb 24, 2020 at 14:24:15 +0000, Daniel Berrange wrote:
On Mon, Feb 24, 2020 at 02:34:16PM +0100, Peter Krempa wrote:
[...]
Would there be any downsides to this that did not already exist in the non-blockdev days ?
We can, but the price is that: 1) we won't allow blockjobs and anything blockdev-related because node name would be out of our control. This was possible in pre-blockdev era.
Ok, that's not viable then. We can't switch one regression for a different regression.
2) we will lose control of actually telling qemu to NOT open the backing file in that case. Distros using only unix permission still have arbitrary file access under permissions of the qemu process.
True, but that is at least historically expected behaviour, which can be fixed by setting <backingfile/> in the XML file IIUC.
Yes, but if you specify any <backingStore> including the terminator you basically configure the image chain yourselves. The part which is configured explicitly will not undergo any form of detection, not even looking for the backing file.
3) weird special-case code, because we need to keep some metadata about the image to do security labelling
I don't think we can solve the regressions in behaviour of backing files by doing probing of the backing files in libvirt, because that only works for the case where libvirt can actually open the file. ie a local file on disk. We don't have logic for opening backing files on RBD, GlusterFS, iSCSI, HTTP, SSH, etc, and nor do we want todo that.
Now we are back in the teritory where we actually do match what would happen with previously. We don't specify these on the command line with ehaviour matching what's described above, with the caveats as above.
I kept this behaviour because we couldn't do better. This is in place even now if the last introspectable image has valid format specified.
We can reconsider how to approach this but ideally separately.
I'm a little lost as to exactly which scenarios are broken, and which we're fixing.
1. file:top.qcow2 -> file:base.raw
2. file:top.qcow2 -> file:base.qcow2
3. file:top.qcow2 -> file:middle.qcow2 -> file:base.raw
4. file:top.qcow2 -> file:middle.qcow2 -> file:base.qcow2
I assume you meant that none of the 'qcow2' files have format of the backing file recorded in the metadata.
IIUC, (1) is working before and now, (2) is working before but broken now, and (3) and (4) were broken before and now.
1) was working before, but is now forbidden 2) was working before, and is now forbidden 3,4) were possibly working (without sVirt), or would get permission denied reported by qemu during startup, currently they are forbidden by a libvirt error message After this patch: 1) will be fixed by this patch 2) will be fixed by this patch 3, 4) will report a libvirt error rather than relying on sVirt or others
So (2) is the only one we /must/ to fix
Am I right that by doing probing in libvirt as per this patch, as well as fixing (2) though, we'll accidentally fix (3) and (4) even though they were always broken before ?
This all talks about qcow2 images on the file: protocol driver. What is the situation for, say, the iscsi: protocol driver
1. iscsi:top.qcow2 -> iscsi:base.raw
2. iscsi:top.qcow2 -> iscsi:base.qcow2
3. iscsi:top.qcow2 -> iscsi:middle.qcow2 -> iscsi:base.raw
4. iscsi:top.qcow2 -> iscsi:middle.qcow2 -> iscsi:base.qcow2
What was the behaviour of this in the pre-blockdev days and vs current git master ? Is it the same with (1) is working before and now, (2) is working before but broken now, and (3) and (4) were broken before and now.
Pre-blockdev and post-blockdev every scenario of the above is working. We can't even inspect the top file for backing store so everything is just ignored. Now what partially changes is when we have something introspectable in the way: 1,2) file:top.qcow2 -> iscsi:base.whatever The current code would report an error if the format was not recorded in the overlay (top.qcow2) and we can't introspect the backing file we'll reject it. This can be relaxed though. 3,4) will work if top.qcow2 has the format but any subsequent don't since we don't introspect it
I'm assuming the libvirt probing cannot fix any case other than file: protocol, or host-device: protocol, since we're unable to open any other type of storage.
It fixes also gluster since the backends for that are already implemented. I'll post another rebased version with some updated docs and one fix. We can continue there perhaps.
On 2/19/20 10:21 AM, Eric Blake wrote:
It took me a few minutes of thinking about this.
Scenario 1:
base.raw <- wrap.qcow2
where wrap.qcow2 specifies backing of base.raw but not the format. If we probe, we can have a couple of outcomes:
1a: base.raw probes as raw (the probed image has no backing or data file), using it as raw is safe (it matches what wrap.qcow2 should have specified but didn't, and we aren't changing the data the guest would read nor are we opening unexpected files)
1b: base.raw probes as qcow2 (because of whatever the guest wrote there), using it as qcow2 is wrong - the guest will see corrupted data. What's more, if the probe sees it as qcow2 with backing file, and we open the backing file, it also has security implications.
Scenario 2:
base.qcow2 <- wrap.qcow2
where wrap.qcow2 specifies backing of base.qcow2 but not the format. If we probe, we will always have just one outcome:
2a: base.qcow2 probes as qcow2. Using it as qcow2 is correct, but if base.qcow2 has a further backing image, the backing chain is now dependent on a probe.
Since 1b and 2a have the same probe result, but massively different data corruption and/or security concerns, it is NOT sufficient to claim that a probe was safe merely because "the probed image does not have any backing or data file". It is ONLY safe if the probe turns up raw. Any other probed format is inherently unsafe.
Having said that, I can offer this heuristic: If the file name itself implies a particular format was intended (such as naming a file *.raw or *.qcow2), and the probe matches what the suffix would imply, we can probably guess that the user did really mean that format (we could even allow *.qcow to resolve to a probe of qcow2, even though qcow and qcow2 are different probe results). File names that do not imply a format (such as 'bare' or 'base.img' or ...) cannot benefit from heuristics. But we just got rid of suffix heuristics in patch 1 of this series. So using file suffix hueristics to accept a filename of 'base.qcow2' that probed as qcow2 as probably being safe, in spite of the missing format, is risky business. While a heuristic might let more pre-existing cases of missing formats boot without data corruption, we have to consider whether the extra magic is helpful or will get in the way for the cases where a management app misnamed their file (calling a file 'base.qcow2' when it is really raw) and such misnaming causes our heuristics to allow data corruption through to the guest. Extra magic that can't go wrong is one thing, but extra magic that can risk data corruption in corner cases where a management app was not careful with their file names is probably not worth the maintenance effort. So I agree with patch 1 removing suffix probing, and think it is not worth trying the file name heuristics just to help management apps that forgot their backing format.
I disagree with the logic here. What we really need is:
If the backing format was not specified, we probe to see what is there. If the result of that probe is raw, it is safe to treat the image as raw. If the result is anything else, we must report an error stating that what we probed could not be trusted unless the user adds an explicit backing format (either confirming that our probe was correct, or with the correct format overriding what we mis-probed).
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
Note that this is not finished yet, but allows to test the image detection patches: Prepare few images: qemu-img create -f qcow2 /tmp/base.qcow2 10M qemu-img create -f qcow2 -b /tmp/base.qcow2 /tmp/overlay1-noformat.qcow2 qemu-img create -f qcow2 -F qcow2 -b /tmp/base.qcow2 /tmp/overlay1-format.qcow2 qemu-img create -f qcow2 -F qcow2 -b /tmp/overlay1-format.qcow2 /tmp/overlay2-format.qcow2 qemu-img create -f qcow2 -b /tmp/overlay1-noformat.qcow2 /tmp/overlay2-noformat.qcow2 qemu-img creage -f qcow2 -b nbd://example/asdf /tmp/nbd-noformat.qcow2 10M (Note that the last one prints error, but that's expected) Probe images: $ ./tests/qemublockprobe -f qcow2 -p /tmp/overlay1-noformat.qcow2 type: file (1) path: /tmp/overlay1-noformat.qcow2 format: qcow2 (14) protocol: none' (0) backing store raw: /tmp/base.qcow2 type: file (1) path: /tmp/base.qcow2 format: qcow2 (14) protocol: none' (0) type: none (0) path: (null) format: none (0) protocol: none' (0) $ ./tests/qemublockprobe -f qcow2 -p /tmp/overlay2-format.qcow2 type: file (1) path: /tmp/overlay2-format.qcow2 format: qcow2 (14) protocol: none' (0) backing store raw: /tmp/overlay1-format.qcow2 type: file (1) path: /tmp/overlay1-format.qcow2 format: qcow2 (14) protocol: none' (0) backing store raw: /tmp/base.qcow2 type: file (1) path: /tmp/base.qcow2 format: qcow2 (14) protocol: none' (0) type: none (0) path: (null) format: none (0) protocol: none' (0) $ ./tests/qemublockprobe -f qcow2 -p /tmp/overlay2-noformat.qcow2 /home/pipo/build/libvirt/gcc/tests/.libs/lt-qemublockprobe: libvirt error: Requested operation is not valid: format of backing image '/tmp/overlay1-noformat.qcow2' of image '/tmp/overlay2-noformat.qcow2' was not specified in the image metadata (See https://libvirt.org/kbase/backing_chains.html for troubleshooting) $ ./tests/qemublockprobe -f qcow2 -p /tmp/nbd-noformat.qcow2 /home/pipo/build/libvirt/gcc/tests/.libs/lt-qemublockprobe: libvirt error: Requested operation is not valid: format of backing image 'nbd://example/asdf' of image '/tmp/nbd-noformat.qcow2' was not specified in the image metadata (See https://libvirt.org/kbase/backing_chains.html for troubleshooting) --- tests/Makefile.am | 13 ++++- tests/qemublockprobe.c | 130 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 142 insertions(+), 1 deletion(-) create mode 100644 tests/qemublockprobe.c diff --git a/tests/Makefile.am b/tests/Makefile.am index ed5255b62d..a47c7eda22 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -291,7 +291,9 @@ test_programs += qemuxml2argvtest qemuxml2xmltest \ qemufirmwaretest \ qemuvhostusertest \ $(NULL) -test_helpers += qemucapsprobe +test_helpers += qemucapsprobe \ + qemublockprobe \ + $(NULL) test_libraries += libqemumonitortestutils.la \ libqemutestdriver.la \ libqemuxml2argvmock.la \ @@ -652,6 +654,14 @@ qemublocktest_LDADD = \ $(qemu_LDADDS) \ $(NULL) +qemublockprobe_SOURCES = \ + qemublockprobe.c \ + $(NULL) +qemublockprobe_LDADD = \ + ../src/libvirt.la \ + $(qemu_LDADDS) \ + $(NULL) + qemudomaincheckpointxml2xmltest_SOURCES = \ qemudomaincheckpointxml2xmltest.c testutilsqemu.c testutilsqemu.h \ testutils.c testutils.h @@ -707,6 +717,7 @@ EXTRA_DIST += qemuxml2argvtest.c qemuxml2xmltest.c \ qemucaps2xmltest.c qemucommandutiltest.c \ qemumemlocktest.c qemucpumock.c testutilshostcpus.h \ qemublocktest.c \ + qemublockprobe.c \ qemumigparamstest.c \ qemusecuritytest.c qemusecuritytest.h \ qemusecuritymock.c \ diff --git a/tests/qemublockprobe.c b/tests/qemublockprobe.c new file mode 100644 index 0000000000..0dbc31028c --- /dev/null +++ b/tests/qemublockprobe.c @@ -0,0 +1,130 @@ +/* + * qemublockprobe.c: image backing chain prober + * + * Copyright (C) 2019 Red Hat, Inc. + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library. If not, see + * <http://www.gnu.org/licenses/>. + */ + +#include <config.h> + +#include <stdio.h> +#include <stdbool.h> + +#include "util/virfile.h" +#include "util/virlog.h" +#include "util/virstoragefile.h" + +#include "virgettext.h" + +#define VIR_FROM_THIS VIR_FROM_QEMU + + +static void +print_source(virStorageSourcePtr src) +{ + size_t i; + + g_print("type: %s (%d)\n", virStorageTypeToString(src->type), src->type); + g_print("path: %s\n", src->path); + g_print("format: %s (%d)\n", virStorageFileFormatTypeToString(src->format), src->format); + g_print("protocol: %s' (%d)\n", virStorageNetProtocolTypeToString(src->protocol), src->protocol); + for (i = 0; i < src->nhosts; i++) { + virStorageNetHostDefPtr h = src->hosts + i; + + g_print("host %zu: name: '%s', port: '%u', transport: '%s'(%d), socket: '%s'\n", + i, h->name, h->port, virStorageNetHostTransportTypeToString(h->transport), + h->transport, h->socket); + } + if (src->sliceStorage) + g_print("slice type: storage, offset: %llu, size: %llu\n", + src->sliceStorage->offset, src->sliceStorage->size); + if (src->backingStoreRaw) + g_print("backing store raw: %s\n", src->backingStoreRaw); + if (src->externalDataStoreRaw) + g_print("external store raw: %s\n", src->externalDataStoreRaw); + if (src->relPath) + g_print("relative path: %s\n", src->relPath); + + g_print("\n"); +} + + +int main(int argc, char **argv) +{ + g_autofree char *path = NULL; + g_autofree char *format = NULL; + g_autoptr(GError) error = NULL; + bool verbose = false; + g_autoptr(virStorageSource) src = NULL; + GOptionContext *ctx; + virStorageSourcePtr n; + int ret = 1; + + GOptionEntry entries[] = { + { "path", 'p', 0, G_OPTION_ARG_STRING, &path, "path to image", "DIR" }, + { "format", 'f', 0, G_OPTION_ARG_STRING, &format, "format of image", "DIR" }, + { "verbose", 'v', 0, G_OPTION_ARG_NONE, &verbose, "Verbose output", NULL }, + { 0 } + }; + + + ctx = g_option_context_new("- inspect an image"); + g_option_context_add_main_entries(ctx, entries, PACKAGE); + if (!g_option_context_parse(ctx, &argc, &argv, &error)) { + g_printerr("%s: option parsing failed: %s\n", + argv[0], error->message); + return 1; + } + + if (!path) { + g_printerr("%s: missing path\n", argv[0]); + return 1; + } + + if (virErrorInitialize() < 0) { + g_printerr("%s: failed to initialize error handling\n", argv[0]); + return 1; + } + + virLogSetFromEnv(); + virFileActivateDirOverrideForProg(argv[0]); + + if (!(src = virStorageSourceNew())) + goto cleanup; + + src->path = g_steal_pointer(&path); + src->type = VIR_STORAGE_TYPE_FILE; + + if (format && + (src->format = virStorageFileFormatTypeFromString(format)) < 0) { + g_printerr("%s: unknown format '%s'\n", argv[0], format); + goto cleanup; + } + + if (virStorageFileGetMetadata(src, -1, -1, true) < 0) + goto cleanup; + + for (n = src; n; n = n->backingStore) + print_source(n); + + ret = 0; + + cleanup: + if (virGetLastErrorCode() != VIR_ERR_OK) + g_printerr("%s: libvirt error: %s\n", argv[0], virGetLastErrorMessage()); + + return ret; +} -- 2.24.1
On 2/17/20 11:13 AM, Peter Krempa wrote:
Note that this is not finished yet, but allows to test the image detection patches:
"allows to ${verb}" is not idiomatic; you want "allows ${verb}ing" or "allows $subject to ${verb}". Here, I would go with "allows testing of the image detection patches".
Prepare few images:
Prepare a few images:
qemu-img create -f qcow2 /tmp/base.qcow2 10M qemu-img create -f qcow2 -b /tmp/base.qcow2 /tmp/overlay1-noformat.qcow2 qemu-img create -f qcow2 -F qcow2 -b /tmp/base.qcow2 /tmp/overlay1-format.qcow2 qemu-img create -f qcow2 -F qcow2 -b /tmp/overlay1-format.qcow2 /tmp/overlay2-format.qcow2 qemu-img create -f qcow2 -b /tmp/overlay1-noformat.qcow2 /tmp/overlay2-noformat.qcow2 qemu-img creage -f qcow2 -b nbd://example/asdf /tmp/nbd-noformat.qcow2 10M
/tmp/overlay1-noformat.qcow2 is inherently unsafe. The probe of /tmp/base.qcow2 returns qcow2, but we cannot trust whether that was because /tmp/base.qcow2 was actually qcow2 or if it was because /tmp/base.qcow2 was raw where the guest wrote a qcow2 header; in the former case our guess is correct, but in the latter case, even though we avoid a security issue of chasing further files under guest control, we do NOT avoid the issue of corrupting guest data (serving the qcow2 payload rather than the qcow2 metadata that the guest wrote in a raw file is guest-visible data corruption).
(Note that the last one prints error, but that's expected)
Probe images:
$ ./tests/qemublockprobe -f qcow2 -p /tmp/overlay1-noformat.qcow2 type: file (1) path: /tmp/overlay1-noformat.qcow2 format: qcow2 (14) protocol: none' (0)
Why the mismatched '?
backing store raw: /tmp/base.qcow2
type: file (1) path: /tmp/base.qcow2 format: qcow2 (14) protocol: none' (0)
type: none (0) path: (null) format: none (0) protocol: none' (0)
The tool needs to report that this image as potentially corrupt (our probe of qcow2 may be correct, or it may be a mistake for what was really raw, and without an explicit backing format, we are unwilling to hand the image to qemu for fear of data corruption visible to the guest, even if we have avoided a security hole of chasing files under guest control).
$ ./tests/qemublockprobe -f qcow2 -p /tmp/overlay2-format.qcow2 type: file (1) path: /tmp/overlay2-format.qcow2 format: qcow2 (14) protocol: none' (0) backing store raw: /tmp/overlay1-format.qcow2
type: file (1) path: /tmp/overlay1-format.qcow2 format: qcow2 (14) protocol: none' (0) backing store raw: /tmp/base.qcow2
type: file (1) path: /tmp/base.qcow2 format: qcow2 (14) protocol: none' (0)
type: none (0) path: (null) format: none (0) protocol: none' (0)
This image is safe.
$ ./tests/qemublockprobe -f qcow2 -p /tmp/overlay2-noformat.qcow2 /home/pipo/build/libvirt/gcc/tests/.libs/lt-qemublockprobe: libvirt error: Requested operation is not valid: format of backing image '/tmp/overlay1-noformat.qcow2' of image '/tmp/overlay2-noformat.qcow2' was not specified in the image metadata (See https://libvirt.org/kbase/backing_chains.html for troubleshooting)
This image is correctly identified as unsafe.
$ ./tests/qemublockprobe -f qcow2 -p /tmp/nbd-noformat.qcow2 /home/pipo/build/libvirt/gcc/tests/.libs/lt-qemublockprobe: libvirt error: Requested operation is not valid: format of backing image 'nbd://example/asdf' of image '/tmp/nbd-noformat.qcow2' was not specified in the image metadata (See https://libvirt.org/kbase/backing_chains.html for troubleshooting)
This image is correctly identified as potentially unsafe because we were unable to probe nbd://example/asdf (had the probe been successful, AND returned a result of raw, then this image would be safe; had the probe been successful but returned anything other than raw, it is no different than the existing failure of the probe being unsuccessful) -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
On Wed, Feb 19, 2020 at 10:31:18 -0600, Eric Blake wrote:
On 2/17/20 11:13 AM, Peter Krempa wrote:
Note that this is not finished yet, but allows to test the image detection patches:
"allows to ${verb}" is not idiomatic; you want "allows ${verb}ing" or "allows $subject to ${verb}". Here, I would go with "allows testing of the image detection patches".
Prepare few images:
Prepare a few images:
qemu-img create -f qcow2 /tmp/base.qcow2 10M qemu-img create -f qcow2 -b /tmp/base.qcow2 /tmp/overlay1-noformat.qcow2 qemu-img create -f qcow2 -F qcow2 -b /tmp/base.qcow2 /tmp/overlay1-format.qcow2 qemu-img create -f qcow2 -F qcow2 -b /tmp/overlay1-format.qcow2 /tmp/overlay2-format.qcow2 qemu-img create -f qcow2 -b /tmp/overlay1-noformat.qcow2 /tmp/overlay2-noformat.qcow2 qemu-img creage -f qcow2 -b nbd://example/asdf /tmp/nbd-noformat.qcow2 10M
/tmp/overlay1-noformat.qcow2 is inherently unsafe. The probe of /tmp/base.qcow2 returns qcow2, but we cannot trust whether that was because /tmp/base.qcow2 was actually qcow2 or if it was because /tmp/base.qcow2 was raw where the guest wrote a qcow2 header; in the former case our guess is correct, but in the latter case, even though we avoid a security issue of chasing further files under guest control, we do NOT avoid the issue of corrupting guest data (serving the qcow2 payload rather than the qcow2 metadata that the guest wrote in a raw file is guest-visible data corruption).
(Note that the last one prints error, but that's expected)
Probe images:
$ ./tests/qemublockprobe -f qcow2 -p /tmp/overlay1-noformat.qcow2 type: file (1) path: /tmp/overlay1-noformat.qcow2 format: qcow2 (14) protocol: none' (0)
Why the mismatched '?
backing store raw: /tmp/base.qcow2
type: file (1) path: /tmp/base.qcow2 format: qcow2 (14) protocol: none' (0)
type: none (0) path: (null) format: none (0) protocol: none' (0)
The tool needs to report that this image as potentially corrupt (our probe of qcow2 may be correct, or it may be a mistake for what was really raw, and without an explicit backing format, we are unwilling to hand the image to qemu for fear of data corruption visible to the guest, even if we have avoided a security hole of chasing files under guest control).
As noted previously, we've used these semantics forever. Prior to introduction of blockdev, we probed the format, but assumed that the image is 'raw' in such case. But we've never reported an error or done anything. We started the VM and let qemu re-probe. This meant that both 'raw' and 'qcow2' images without a backing file were working without a hitch even with sVirt. Users not having the benefit of sVirt were also possibly still seeing possible unwanted access. I'm specifically interrested in keeping both 'raw' and single layer 'qcow2' work as they did before because in my opinion it's not worse than it was before when running qemu where libvirt wouldn't use blockdev and _strictly_ better in case when we do use -blockdev, while not making many users unhappy. And there were already a lot of unhappy users.
participants (3)
-
Daniel P. Berrangé -
Eric Blake -
Peter Krempa