fuse: don't keep dead fuse_conn at fuse_fill_super().

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@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+ec3986119086fe4eec97@syzkaller.appspotmail.com>
Fixes: 3b463ae0c626 ("fuse: invalidation reverse calls")
Cc: John Muir <john@jmuir.com>
Cc: Csaba Henk <csaba@gluster.com>
Cc: Anand Avati <avati@redhat.com>
Cc: <stable@vger.kernel.org> # v2.6.31
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 94a745acaef842eed799e45731bd12dd2ac0f7f7..a13ecefa9cd1f1b9705ec6b124fd060fa1fd4ed4 100644 (file)
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1176,6 +1176,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
        fuse_dev_free(fud);
  err_put_conn:
        fuse_conn_put(fc);
+       sb->s_fs_info = NULL;
  err_fput:
        fput(file);
  err: