8:25 a.m.
On 5/25/20 1:14 PM, Christian Ehrhardt wrote:
On Mon, May 18, 2020 at 10:07 AM Michal Privoznik
<mprivozn(a)redhat.com> wrote:
>
> On 5/18/20 10:02 AM, Erik Skultety wrote:
>
>> Yes, I know, what I meant by "unrelated" here was just the fact that in
order
>> to fix Apparmor, you only need the first hunk, I guess I'll be more explicit
>> next time :). It's true that with the first hunk the second becomes
redundant,
>> but I still feel like the NOP driver should cover the full spectrum of
>> operations we support, but maybe I'm trying to be overly cautious here.
>>
>
> Well, it doesn't implement everything already. But okay, I have ACK for
> the important hunk so I will push only that one.
Hi Michal,
while debugging a Ubuntu bug report I found that this fix will
mitigate the warning you wanted to fix.
But overall there still is an issue with the labeling introduced by
[1][2] in >=5.6.
The situation (related to this fix, hence replying in this context) is
the following.
Ubuntu (as an example) builds and has build with --without-attr.
That will make the code have !HAVE_LIBATTR which was fine in the past.
But with your code added the LP bug [3] identified an issue.
What happens is that in stacked security it will iterate on:
- virSecurityStackMoveImageMetadata (for the stacking itself)
- 0x0 (apparmor)
- virSecurityDACMoveImageMetadata
The fix discussed here fixes the warning emitted by the apparmor case like:
"this function is not supported by the connection driver"
But when iterating further on a build that has no attr support we
encounter the following (e.g. at guest shutdown):
libvirtd[6320]: internal error: child reported (status=125):
libvirtd[6320]: Unable to remove disk metadata on vm testguest from
/var/lib/uvtool/libvirt/images/testguest.qcow (disk target vda)
I found that this is due to:
qemuBlockRemoveImageMetadata (the one that emits the warning)
-> qemuSecurityMoveImageMetadata
-> virSecurityManagerMoveImageMetadata
-> virSecurityDACMoveImageMetadata
-> virSecurityDACMoveImageMetadataHelper
-> virProcessRunInFork (spawns subprocess)
-> virSecurityMoveRememberedLabel
Since this is built without HAVE_LIBATTR the following will happen
461 if (virFileGetXAttrQuiet(src, ref_name, &ref_value) < 0) {
(gdb) n
462 if (errno == ENOSYS || errno == ENOTSUP) {
(gdb) p errno
$32 = 38
And that is due to !HAVE_LIBATTR which maps the implementation onto:
4412 #else /* !HAVE_LIBATTR */
4413
4414 int
4415 virFileGetXAttrQuiet(const char *path G_GNUC_UNUSED,
4416 const char *name G_GNUC_UNUSED,
4417 char **value G_GNUC_UNUSED)
4418 {
4419 errno = ENOSYS;
4420 return -1;
4421 }
Due to that we see the two messages reported above
a) internal errors -> for the subprocess that failed
b) "Unable to remove disk metadata" -> but this time due to DAC
instead of apparmor in the security stack
Thank you for your deep analysis.
I'm not sure what you'd prefer Michal, maybe an early RC=0 exit in
virSecurityMoveRememberedLabel in case of !HAVE_LIBATTR?
Con: That would still fork the process to do nothing then
Pro: It would but be a small change in just one place
Since you did all the related changes I thought I report the case and
leave it up to you Michal, what do you think?
Yes, a naive fix would be something like this:
diff --git i/src/security/security_dac.c w/src/security/security_dac.c
index bdc2d7edf3..7b95a6f86d 100644
--- i/src/security/security_dac.c
+++ w/src/security/security_dac.c
@@ -1117,6 +1117,12 @@ virSecurityDACMoveImageMetadataHelper(pid_t pid
G_GNUC_UNUSED,
ret = virSecurityMoveRememberedLabel(SECURITY_DAC_NAME, data->src,
data->dst);
virSecurityManagerMetadataUnlock(data->mgr, &state);
+
+ if (ret == -2) {
+ /* Libvirt built without XATTRS */
+ ret = 0;
+ }
+
return ret;
}
But as you correctly say, it will still lead to an unnecessary spawn of
a process that will do NOP (basically). I think a better fix would be to
not require .domainMoveImageMetadata callbacks (i.e. the one from NOP
driver could be then removed) and set the DAC/SELinux callbacks if and
only if HAVE_LIBATTR; alternatively, make those functions be NOP if
!HAVE_LIBATTR.
On the other hand, every time we relabel a path outside of /dev, we
technically spawn unnecessary because only /dev lives inside a private
NS. Everything else is from the parent NS. For instance, there is no
need to spawn only to chown("/var/lib/libvirt/images/fedora.qcow2").
Therefore I might have a slight preference for the naive fix, but I will
leave it up to you. Or do you want me to sent the patch?
Michal