Re: [libvirt] [PATCH v2 7/7] qemu_security: Lock metadata while relabelling

20 Aug 2018

On 08/17/2018 08:38 PM, John Ferlan wrote:
...
On 08/14/2018 07:19 AM, Michal Privoznik wrote:
...
Fortunately, we have qemu wrappers so it's sufficient to put
lock/unlock call only there.
Kind of sparse... Maybe a few words related to what benefit locking the
metadata provides. There is a danger in all this too if the unlock does
fail since metadata locks are wait type locks any subsequent lock will wait.
...
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 src/qemu/qemu_security.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)

diff --git a/src/qemu/qemu_security.c b/src/qemu/qemu_security.c
index af3be42854..527563947c 100644
--- a/src/qemu/qemu_security.c
+++ b/src/qemu/qemu_security.c
@@ -26,6 +26,7 @@
 #include "qemu_domain.h"
 #include "qemu_security.h"
 #include "virlog.h"
+#include "locking/domain_lock.h"
#define VIR_FROM_THIS VIR_FROM_QEMU
@@ -39,6 +40,12 @@ qemuSecuritySetAllLabel(virQEMUDriverPtr driver,
 {
     int ret = -1;
     qemuDomainObjPrivatePtr priv = vm->privateData;
+    bool locked = false;
+
+    if (virDomainLockMetadataLock(driver->lockManager, vm) < 0)
+        goto cleanup;
+
+    locked = true;
if (qemuDomainNamespaceEnabled(vm, QEMU_DOMAIN_NS_MOUNT) &&
         virSecurityManagerTransactionStart(driver->securityManager) < 0)
@@ -55,9 +62,17 @@ qemuSecuritySetAllLabel(virQEMUDriverPtr driver,
                                             vm->pid) < 0)
         goto cleanup;
+    locked = false;
Technically not true yet. Also , I think two such attempts with the
second eliciting the VIR_WARN is perfectly reasonable (IOW: on failure
of the following goto cleanup with locked == true, try again, and spew
that message).
This repeats a few times, but I'll note just once.
I don't think it is safe to unlock something twice if we've locked it
just once.
...
...
+
+    if (virDomainLockMetadataUnlock(driver->lockManager, vm) < 0)
+        goto cleanup;
+
     ret = 0;
  cleanup:
     virSecurityManagerTransactionAbort(driver->securityManager);
+    if (locked &&
+        virDomainLockMetadataUnlock(driver->lockManager, vm) < 0)
+        VIR_WARN("unable to release metadata lock");
Should we add the  @stdin_path and @vm->pid and/or vm->name here? It may
help some day. Similar comments for other new VIR_WARN's, but the
parameters change...
Ah, good point. Okay.
...
...
return ret;
 }
@@ -68,6 +83,10 @@ qemuSecurityRestoreAllLabel(virQEMUDriverPtr driver,
                             bool migrated)
 {
     qemuDomainObjPrivatePtr priv = vm->privateData;
+    bool unlock = true;
+
+    if (virDomainLockMetadataLock(driver->lockManager, vm) < 0)
+        unlock = false;
/* In contrast to qemuSecuritySetAllLabel, do not use
      * secdriver transactions here. This function is called from
@@ -79,6 +98,10 @@ qemuSecurityRestoreAllLabel(virQEMUDriverPtr driver,
                                       vm->def,
                                       migrated,
                                       priv->chardevStdioLogd);
+
+    if (unlock &&
+        virDomainLockMetadataUnlock(driver->lockManager, vm) < 0)
+        VIR_WARN("unable to release metadata lock");
 }
@@ -88,6 +111,12 @@ qemuSecuritySetDiskLabel(virQEMUDriverPtr driver,
                          virDomainDiskDefPtr disk)
 {
     int ret = -1;
+    bool locked = false;
+
+    if (virDomainLockMetadataDiskLock(driver->lockManager, vm, disk) < 0)
+        goto cleanup;
+
+    locked = true;
if (qemuDomainNamespaceEnabled(vm, QEMU_DOMAIN_NS_MOUNT) &&
         virSecurityManagerTransactionStart(driver->securityManager) < 0)
@@ -103,9 +132,17 @@ qemuSecuritySetDiskLabel(virQEMUDriverPtr driver,
                                             vm->pid) < 0)
         goto cleanup;
+    locked = false;
+
+    if (virDomainLockMetadataDiskUnlock(driver->lockManager, vm, disk) < 0)
+        goto cleanup;
+
     ret = 0;
  cleanup:
     virSecurityManagerTransactionAbort(driver->securityManager);
+    if (locked &&
+        virDomainLockMetadataDiskUnlock(driver->lockManager, vm, disk) < 0)
+        VIR_WARN("unable to release disk metadata lock");
     return ret;
 }
@@ -116,6 +153,12 @@ qemuSecurityRestoreDiskLabel(virQEMUDriverPtr driver,
                              virDomainDiskDefPtr disk)
 {
     int ret = -1;
+    bool locked = false;
+
+    if (virDomainLockMetadataDiskLock(driver->lockManager, vm, disk) < 0)
+        goto cleanup;
+
+    locked = true;
if (qemuDomainNamespaceEnabled(vm, QEMU_DOMAIN_NS_MOUNT) &&
         virSecurityManagerTransactionStart(driver->securityManager) < 0)
@@ -131,9 +174,17 @@ qemuSecurityRestoreDiskLabel(virQEMUDriverPtr driver,
                                             vm->pid) < 0)
         goto cleanup;
+    locked = false;
+
+    if (virDomainLockMetadataDiskUnlock(driver->lockManager, vm, disk) < 0)
+        goto cleanup;
+
     ret = 0;
  cleanup:
     virSecurityManagerTransactionAbort(driver->securityManager);
+    if (locked &&
+        virDomainLockMetadataDiskUnlock(driver->lockManager, vm, disk) < 0)
+        VIR_WARN("unable to release disk metadata lock");
     return ret;
 }
@@ -144,6 +195,12 @@ qemuSecuritySetImageLabel(virQEMUDriverPtr driver,
                           virStorageSourcePtr src)
 {
     int ret = -1;
+    bool locked = false;
+
+    if (virDomainLockMetadataImageLock(driver->lockManager, vm, src) < 0)
+        goto cleanup;
+
+    locked = true;
if (qemuDomainNamespaceEnabled(vm, QEMU_DOMAIN_NS_MOUNT) &&
         virSecurityManagerTransactionStart(driver->securityManager) < 0)
@@ -159,9 +216,17 @@ qemuSecuritySetImageLabel(virQEMUDriverPtr driver,
                                             vm->pid) < 0)
         goto cleanup;
+    locked = false;
+
+    if (virDomainLockMetadataImageUnlock(driver->lockManager, vm, src) < 0)
+        goto cleanup;
+
     ret = 0;
  cleanup:
     virSecurityManagerTransactionAbort(driver->securityManager);
+    if (locked &&
+        virDomainLockMetadataImageUnlock(driver->lockManager, vm, src) < 0)
+        VIR_WARN("unable to release image metadata lock");
     return ret;
 }
@@ -172,6 +237,12 @@ qemuSecurityRestoreImageLabel(virQEMUDriverPtr driver,
                               virStorageSourcePtr src)
 {
     int ret = -1;
+    bool locked = false;
+
+    if (virDomainLockMetadataImageLock(driver->lockManager, vm, src) < 0)
+        goto cleanup;
+
+    locked = true;
if (qemuDomainNamespaceEnabled(vm, QEMU_DOMAIN_NS_MOUNT) &&
         virSecurityManagerTransactionStart(driver->securityManager) < 0)
@@ -187,9 +258,17 @@ qemuSecurityRestoreImageLabel(virQEMUDriverPtr driver,
                                             vm->pid) < 0)
         goto cleanup;
+    locked = false;
+
+    if (virDomainLockMetadataImageUnlock(driver->lockManager, vm, src) < 0)
+        goto cleanup;
+
     ret = 0;
  cleanup:
     virSecurityManagerTransactionAbort(driver->securityManager);
+    if (locked &&
+        virDomainLockMetadataImageUnlock(driver->lockManager, vm, src) < 0)
+        VIR_WARN("unable to release image metadata lock");
     return ret;
 }
Just below here is HostdevLabel processing... For a SCSI host device
that would seem to cover the type of resource described in the cover
letter to patch6 - at least for iSCSI LUNs (and of course vHBA LUNs).
Need to look at the hostdev->mode and hostdev->source.subsys.type and
dig into the subsys.u.scsi to get to the src->path.
Oh, this was the reason I made VIR_WARN() so sparse. I did not wanted to
get into business of getting paths from all the complicated structs we
have. I'll just put vm->def->name and vm->pid into the warn message.

Michal

    

Re: [libvirt] [PATCH v2 7/7] qemu_security: Lock metadata while relabelling

Michal Prívozník