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