On Wed, Mar 20, 2019 at 12:40:50AM -0500, Eric Blake wrote:
The following virsh command was triggering a use-after-free:$ virsh -c test:///default ' snapshot-create-as test s1 snapshot-create-as test s2 snapshot-delete --children-only test s1 snapshot-current --name test' Domain snapshot s1 created Domain snapshot s2 created Domain snapshot s1 children deleted error: name in virGetDomainSnapshot must not be NULL I got lucky on that run - although the error message is quite unexpected. On other runs, I was able to get a core dump, and valgrind confirms there is a definitive problem. The culprit? We were inconsistent about whether we set vm->current_snapshot, snap->def->current, or both when updating how the current snapshot was being tracked. As a result, deletion did not see that snapshot s2 was previously current, and failed to update vm->current_snapshot, so that the next API using the current snapshot failed because it referenced stale memory for the now-gone s2 (instead of the intended s1). The test driver code was copied from the qemu code (which DOES track both pieces of state everywhere), but was purposefully simplified because the test driver does not have to write persistent snapshot state to the file system. But when you realize that the only reason snap->def->current needs to exist is when writing out one file per snapshot for qemu, it's just as easy to state that the test driver never has to mess with the field (rather than chasing down which places forgot to set the field), and have vm->current_snapshot be the sole source of truth in the test driver. Ideally, I'd get rid of the 'current' member in virDomainSnapshotDef, as well as the 'current_snapshot' member in virDomainDef, and instead track the current member in virDomainSnapshotObjList, coupled with writing ALL snapshot state for qemu in a single file (where I can use <snapshots current='...'> as a wrapper, rather than VIR_DOMAIN_SNAPSHOT_FORMAT_INTERNAL to output <current>1</current> XML on a per-snapshot file basis). But that's a bigger change, so for now I'm just patching things to avoid the test driver segfault. Signed-off-by: Eric Blake <ebl...@redhat.com> --- src/test/test_driver.c | 19 +++++-------------- 1 file changed, 5 insertions(+), 14 deletions(-)
Reviewed-by: Ján Tomko <jto...@redhat.com> Jano
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