| Message ID | 20250304080213.36099-1-gerben@altlinux.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | block/snapshot: fix *errp handling in bdrv_snapshot_goto | expand |
Am 04.03.2025 um 09:01 hat gerben@altlinux.org geschrieben: > From: Denis Rastyogin <gerben@altlinux.org> > > This error was discovered by fuzzing qemu-img. > > If bdrv_snapshot_goto() returns an error, it is not handled immediately, > allowing *errp to be reassigned when qcow_open() fails, which triggers > assert(*errp == NULL) in util/error.c: void error_setv(). > > This patch ensures that errors from bdrv_snapshot_goto() are handled > immediately after the call, preventing *errp from being modified twice > and avoiding unnecessary assertion failures. > > Closes: https://gitlab.com/qemu-project/qemu/-/issues/2851 > Signed-off-by: Denis Rastyogin <gerben@altlinux.org> > --- > block/snapshot.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/block/snapshot.c b/block/snapshot.c > index 9c44780e96..d1b5a8d33d 100644 > --- a/block/snapshot.c > +++ b/block/snapshot.c > @@ -296,14 +296,20 @@ int bdrv_snapshot_goto(BlockDriverState *bs, > bdrv_graph_wrunlock(); > > ret = bdrv_snapshot_goto(fallback_bs, snapshot_id, errp); > + if (ret < 0) { > + bdrv_unref(fallback_bs); > + bs->drv = NULL; > + /* A bdrv_snapshot_goto() error takes precedence */ > + error_propagate(errp, local_err); > + return ret; > + } Now you return without having reopened the image! > open_ret = drv->bdrv_open(bs, options, bs->open_flags, &local_err); > qobject_unref(options); > if (open_ret < 0) { > bdrv_unref(fallback_bs); > bs->drv = NULL; > - /* A bdrv_snapshot_goto() error takes precedence */ > error_propagate(errp, local_err); > - return ret < 0 ? ret : open_ret; > + return open_ret; > } I don't see a problem in the old code. local_err is still NULL at this point, so it's safe to pass it to drv->bdrv_open(). A previous error from bdrv_snapshot_goto() is stored in errp, which is separate. The line in qcow.c (test.qed is misleading as a filename!) that causes the assertion failure is this: error_setg(&s->migration_blocker, "The qcow format used by node '%s' " "does not support live migration", bdrv_get_device_or_node_name(bs)); This is an internal field that is not related to either error in bdrv_snapshot_goto(). This is another instance of the same bug that bs->opaque needs to be zeroed before calling drv->bdrv_open(). I sent a patch for that. Kevin
diff --git a/block/snapshot.c b/block/snapshot.c index 9c44780e96..d1b5a8d33d 100644 --- a/block/snapshot.c +++ b/block/snapshot.c @@ -296,14 +296,20 @@ int bdrv_snapshot_goto(BlockDriverState *bs, bdrv_graph_wrunlock(); ret = bdrv_snapshot_goto(fallback_bs, snapshot_id, errp); + if (ret < 0) { + bdrv_unref(fallback_bs); + bs->drv = NULL; + /* A bdrv_snapshot_goto() error takes precedence */ + error_propagate(errp, local_err); + return ret; + } open_ret = drv->bdrv_open(bs, options, bs->open_flags, &local_err); qobject_unref(options); if (open_ret < 0) { bdrv_unref(fallback_bs); bs->drv = NULL; - /* A bdrv_snapshot_goto() error takes precedence */ error_propagate(errp, local_err); - return ret < 0 ? ret : open_ret; + return open_ret; } /*