From: Greg Kurz groug@kaod.org
stable inclusion from stable-5.10.50 commit 91c2aa2c64b8d7a973407e6e3e1d012b1a352ad0 bugzilla: 174522 https://gitee.com/openeuler/kernel/issues/I4DNFY
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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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
Signed-off-by: Chen Jun chenjun102@huawei.com Acked-by: Weilong Chen chenweilong@huawei.com Signed-off-by: Chen Jun chenjun102@huawei.com --- fs/fuse/dir.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c index ffa031fe5293..d99bf6207b16 100644 --- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -340,8 +340,12 @@ 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);