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snapshot: Don't hose list on deletion failure

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If qemuDomainSnapshotDiscard() fails for any reason (rare,
but possible with an ill-timed ENOMEM or if
qemuDomainSnapshotForEachQcow2() has problems talking to the
qemu guest monitor), then an attempt to retry the snapshot
deletion API will crash because we didn't undo the effects
of virDomainSnapshotDropParent() temporarily rearranging the
internal list structures, and the second attempt to drop
parents will dereference NULL.  Fix it by instead noting that
there are only two callers to qemuDomainSnapshotDiscard(),
and only one of the two callers wants the parent to be updated;
thus we can move the call to virDomainSnapshotDropParent()
into a code path that only gets executed on success.

Signed-off-by: Eric Blake <eblake@redhat.com>
ACKed-by: Michal Privoznik <mprivozn@redhat.com>
This commit is contained in:
Eric Blake 2018-10-17 19:24:34 -05:00
parent 2569ba1338
commit 68b2596f83
2 changed files with 4 additions and 3 deletions
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6
src/qemu/qemu_domain.c
View File

@ -8249,7 +8249,7 @@ int
qemuDomainSnapshotDiscard(virQEMUDriverPtr driver, qemuDomainSnapshotDiscard(virQEMUDriverPtr driver,
virDomainObjPtr vm, virDomainObjPtr vm,
virDomainSnapshotObjPtr snap, virDomainSnapshotObjPtr snap,
bool update_current, bool update_parent,
bool metadata_only) bool metadata_only)
{ {
char *snapFile = NULL; char *snapFile = NULL;
@ -8278,7 +8278,7 @@ qemuDomainSnapshotDiscard(virQEMUDriverPtr driver,
goto cleanup; goto cleanup;
if (snap == vm->current_snapshot) { if (snap == vm->current_snapshot) {
if (update_current && snap->def->parent) { if (update_parent && snap->def->parent) {
parentsnap = virDomainSnapshotFindByName(vm->snapshots, parentsnap = virDomainSnapshotFindByName(vm->snapshots,
snap->def->parent); snap->def->parent);
if (!parentsnap) { if (!parentsnap) {
@ -8301,6 +8301,8 @@ qemuDomainSnapshotDiscard(virQEMUDriverPtr driver,
if (unlink(snapFile) < 0) if (unlink(snapFile) < 0)
VIR_WARN("Failed to unlink %s", snapFile); VIR_WARN("Failed to unlink %s", snapFile);
if (update_parent)
virDomainSnapshotDropParent(snap);
virDomainSnapshotObjListRemove(vm->snapshots, snap); virDomainSnapshotObjListRemove(vm->snapshots, snap);
ret = 0; ret = 0;

1
src/qemu/qemu_driver.c
View File

@ -16526,7 +16526,6 @@ qemuDomainSnapshotDelete(virDomainSnapshotPtr snapshot,
snap->first_child = NULL; snap->first_child = NULL;
ret = 0; ret = 0;
} else { } else {
virDomainSnapshotDropParent(snap);
ret = qemuDomainSnapshotDiscard(driver, vm, snap, true, metadata_only); ret = qemuDomainSnapshotDiscard(driver, vm, snap, true, metadata_only);
} }