| Message ID | 20210525150230.157586-2-groug@kaod.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fuse: Some fixes for submounts | expand |
On 25.05.21 17:02, Greg Kurz wrote: > If fuse_fill_super_submount() returns an error, the error path > triggers a crash: > > [ 26.206673] BUG: kernel NULL pointer dereference, address: 0000000000000000 > [...] > [ 26.226362] RIP: 0010:__list_del_entry_valid+0x25/0x90 > [...] > [ 26.247938] Call Trace: > [ 26.248300] fuse_mount_remove+0x2c/0x70 [fuse] > [ 26.248892] virtio_kill_sb+0x22/0x160 [virtiofs] > [ 26.249487] deactivate_locked_super+0x36/0xa0 > [ 26.250077] fuse_dentry_automount+0x178/0x1a0 [fuse] > > The crash happens because fuse_mount_remove() assumes that the FUSE > mount was already added to list under the FUSE connection, but this > only done after fuse_fill_super_submount() has returned success. > > This means that until fuse_fill_super_submount() has returned success, > the FUSE mount isn't actually owned by the superblock. We should thus > reclaim ownership by clearing sb->s_fs_info, which will skip the call > to fuse_mount_remove(), and perform rollback, like virtio_fs_get_tree() > already does for the root sb. > > Fixes: bf109c64040f ("fuse: implement crossmounts") > Cc: mreitz@redhat.com > Cc: stable@vger.kernel.org # v5.10+ > Signed-off-by: Greg Kurz <groug@kaod.org> > --- > fs/fuse/dir.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) Reviewed-by: Max Reitz <mreitz@redhat.com>
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c index 1b6c001a7dd1..01559061cbfb 100644 --- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -339,8 +339,12 @@ static struct vfsmount *fuse_dentry_automount(struct path *path) /* Initialize superblock, making @mp_fi its root */ err = fuse_fill_super_submount(sb, mp_fi); - if (err) + if (err) { + fuse_conn_put(fc); + kfree(fm); + sb->s_fs_info = NULL; goto out_put_sb; + } sb->s_flags |= SB_ACTIVE; fsc->root = dget(sb->s_root);
If fuse_fill_super_submount() returns an error, the error path triggers a crash: [ 26.206673] BUG: kernel NULL pointer dereference, address: 0000000000000000 [...] [ 26.226362] RIP: 0010:__list_del_entry_valid+0x25/0x90 [...] [ 26.247938] Call Trace: [ 26.248300] fuse_mount_remove+0x2c/0x70 [fuse] [ 26.248892] virtio_kill_sb+0x22/0x160 [virtiofs] [ 26.249487] deactivate_locked_super+0x36/0xa0 [ 26.250077] fuse_dentry_automount+0x178/0x1a0 [fuse] The crash happens because fuse_mount_remove() assumes that the FUSE mount was already added to list under the FUSE connection, but this only done after fuse_fill_super_submount() has returned success. This means that until fuse_fill_super_submount() has returned success, the FUSE mount isn't actually owned by the superblock. We should thus reclaim ownership by clearing sb->s_fs_info, which will skip the call to fuse_mount_remove(), and perform rollback, like virtio_fs_get_tree() already does for the root sb. Fixes: bf109c64040f ("fuse: implement crossmounts") Cc: mreitz@redhat.com Cc: stable@vger.kernel.org # v5.10+ Signed-off-by: Greg Kurz <groug@kaod.org> --- fs/fuse/dir.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)