[PATCH 4.9 022/101] fuse: dont keep dead fuse_conn at fuse_fill_super().

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

commit 543b8f8662fe6d21f19958b666ab0051af9db21a upstream.

syzbot is reporting use-after-free at fuse_kill_sb_blk() [1].
Since sb->s_fs_info field is not cleared after fc was released by
fuse_conn_put() when initialization failed, fuse_kill_sb_blk() finds
already released fc and tries to hold the lock. Fix this by clearing
sb->s_fs_info field after calling fuse_conn_put().

[1] https://syzkaller.appspot.com/bug?id=a07a680ed0a9290585ca424546860464dd9658db

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Reported-by: syzbot <syzbot+ec3986119086fe4eec97@xxxxxxxxxxxxxxxxxxxxxxxxx>
Fixes: 3b463ae0c626 ("fuse: invalidation reverse calls")
Cc: John Muir <john@xxxxxxxxx>
Cc: Csaba Henk <csaba@xxxxxxxxxxx>
Cc: Anand Avati <avati@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v2.6.31
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/fuse/inode.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1184,6 +1184,7 @@ static int fuse_fill_super(struct super_
  err_put_conn:
 	fuse_bdi_destroy(fc);
 	fuse_conn_put(fc);
+	sb->s_fs_info = NULL;
  err_fput:
 	fput(file);
  err: