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libxl: Fix possible object refcnt issue

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When libxlDomainMigrationDstPrepare adds the @args to an
virNetSocketAddIOCallback using libxlMigrateDstReceive as
the target of the virNetSocketIOFunc @func with the knowledge
that the libxlMigrateDstReceive will virObjectUnref @args
at the end thus not needing to Unref during normal processing
for libxlDomainMigrationDstPrepare.

However, Coverity believes there's an issue with this. The
problem is there can be @nsocks virNetSocketAddIOCallback's
added, but only one virObjectUnref. That means the first
one done will Unref and the subsequent callers may not get
the @args (or @opaque) as they expected. If there's only
one socket returned from virNetSocketNewListenTCP, then sure
that works. However, if it returned more than one there's
going to be a problem.

To resolve this, since we start with 1 reference from the
virObjectNew for @args, we will add 1 reference for each
time @args is used for virNetSocketAddIOCallback. Then
since libxlDomainMigrationDstPrepare would be done with
@args, move it's virObjectUnref from the error: label to
the done: label (since error: falls through). That way
once the last IOCallback is done, then @args will be freed.

Signed-off-by: John Ferlan <jferlan@redhat.com>
ACKed-by: Michal Privoznik <mprivozn@redhat.com>
This commit is contained in:
John Ferlan 2018-09-27 17:41:07 -04:00
parent 6830c81307
commit 425b9f8aa6
1 changed files with 2 additions and 2 deletions
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4
src/libxl/libxl_migration.c
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@ -793,7 +793,7 @@ libxlDomainMigrationDstPrepare(virConnectPtr dconn,
if (virNetSocketAddIOCallback(socks[i],
VIR_EVENT_HANDLE_READABLE,
libxlMigrateDstReceive,
args,
virObjectRef(args),
NULL) < 0)
continue;
@ -815,7 +815,6 @@ libxlDomainMigrationDstPrepare(virConnectPtr dconn,
virObjectUnref(socks[i]);
}
VIR_FREE(socks);
virObjectUnref(args);
if (priv) {
virPortAllocatorRelease(priv->migrationPort);
priv->migrationPort = 0;
@ -831,6 +830,7 @@ libxlDomainMigrationDstPrepare(virConnectPtr dconn,
VIR_FREE(hostname);
else
virURIFree(uri);
virObjectUnref(args);
virDomainObjEndAPI(&vm);
virObjectUnref(cfg);
return ret;