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Subject: Re: [syzbot] general protection fault in hctx_lock
To:     syzbot <syzbot+005b78d4c45263d656dd@syzkaller.appspotmail.com>,
        hch@lst.de, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
References: <000000000000c7c18505ce93467e@google.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <23531d29-9d96-6744-bab9-797e65379037@kernel.dk>
Date:   Sun, 17 Oct 2021 16:03:39 -0600
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On 10/17/21 3:40 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    7c832d2f9b95 Add linux-next specific files for 20211015
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=10e9df10b00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f6ac42766a768877
> dashboard link: https://syzkaller.appspot.com/bug?extid=005b78d4c45263d656dd
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1154f80cb00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1750eeecb00000
> 
> The issue was bisected to:
> 
> commit f328476e373a7ce4b4d16c48fe85571044e025f5
> Author: Christoph Hellwig <hch@lst.de>
> Date:   Tue Oct 12 10:40:45 2021 +0000
> 
>     blk-mq: cleanup blk_mq_submit_bio

It's a potential use-after-free using rq->mq_hctx after inserting a flush.
I'll fold in a fix, as I'm shuffling things around anyway.

-- 
Jens Axboe