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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        syzbot <syzbot+ec3986119086fe4eec97@syzkaller.appspotmail.com>,
        John Muir <john@jmuir.com>, Csaba Henk <csaba@gluster.com>,
        Anand Avati <avati@redhat.com>,
        Miklos Szeredi <mszeredi@redhat.com>
Subject: [PATCH 4.4 041/105] fuse: dont keep dead fuse_conn at fuse_fill_super().
Date:   Sun,  1 Jul 2018 18:01:51 +0200
Message-Id: <20180701153152.186327132@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

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>

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

--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1158,6 +1158,7 @@ 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: