Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 5.13 120/800] fuse: Fix crash in fuse_dentry_automount() error path | Date | Mon, 12 Jul 2021 08:02:23 +0200 |
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From: Greg Kurz <groug@kaod.org>
commit d92d88f0568e97c437eeb79d9c9609bd8277406f upstream.
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: stable@vger.kernel.org # v5.10+ Signed-off-by: Greg Kurz <groug@kaod.org> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- fs/fuse/dir.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
--- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -339,8 +339,12 @@ static struct vfsmount *fuse_dentry_auto /* 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);
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