linux-kernel - Re: KASAN: use-after-free Read in fuse_kill_sb

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Date:   Tue, 1 May 2018 19:03:05 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     syzbot <syzbot+ec3986119086fe4eec97@...kaller.appspotmail.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        miklos@...redi.hu, syzkaller-bugs@...glegroups.com,
        Anand Avati <avati@...hat.com>, Csaba Henk <csaba@...ster.com>,
        John Muir <john@...ir.com>
Subject: Re: KASAN: use-after-free Read in fuse_kill_sb_blk

>From 606d54cd24b5b00e7a7e3597aabbe89719defc56 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Tue, 1 May 2018 13:12:14 +0900
Subject: [PATCH] fuse: don't keep dead fuse_conn at fuse_fill_super().

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@...ove.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+ec3986119086fe4eec97@...kaller.appspotmail.com>
Fixes: 3b463ae0c6264f70 ("fuse: invalidation reverse calls")
Cc: John Muir <john@...ir.com>
Cc: Csaba Henk <csaba@...ster.com>
Cc: Anand Avati <avati@...hat.com>
Cc: Miklos Szeredi <mszeredi@...hat.com>
---
 fs/fuse/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index ef30995..9b37cf8 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1179,6 +1179,7 @@ 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:
-- 
1.8.3.1