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Subject: Re: upstream boot error: can't ssh into the instance (2)
To:     Dmitry Vyukov <dvyukov@google.com>, linux-block@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>
Cc:     syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        syzbot <syzbot+4df6ca820108fd248943@syzkaller.appspotmail.com>,
        Ming Lei <ming.lei@redhat.com>
References: <00000000000027601e05806bf6be@google.com>
 <CACT4Y+aH2wo8rdaiZJd7s6Ct3b8mDeuvOj8CsvystV9T10+b-g@mail.gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <ace6b631-3e4b-3da5-f280-463a1bb41d97@kernel.dk>
Date:   Sun, 27 Jan 2019 06:35:18 -0700
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On 1/27/19 1:05 AM, Dmitry Vyukov wrote:
> On Sun, Jan 27, 2019 at 9:01 AM syzbot
> <syzbot+4df6ca820108fd248943@syzkaller.appspotmail.com> wrote:
>>
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    7930851ef10c Merge tag 'scsi-fixes' of git://git.kernel.or..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=1002c77f400000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=505743eba4e4f68
>> dashboard link: https://syzkaller.appspot.com/bug?extid=4df6ca820108fd248943
>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>>
>> Unfortunately, I don't have any reproducer for this crash yet.
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+4df6ca820108fd248943@syzkaller.appspotmail.com
> 
> 
> Mainline tree crashes on boot.
> +generic_make_request maintainers
> 
> [    7.485069] ==================================================================
> [    7.486411] BUG: KASAN: use-after-free in generic_make_request+0x14dd/0x1810
> [    7.487539] Read of size 2 at addr ffff8880a39618d4 by task swapper/0/1
> [    7.488689]

Ah duh, not sure how I missed that:

+                       bio_set_flag(bio, BIO_QUEUE_ENTERED);
                        ret = q->make_request_fn(q, bio);
+                       bio_clear_flag(bio, BIO_QUEUE_ENTERED);

Ming, we can't touch bio after ->make_request_fn(), it could very well be
completed already.

-- 
Jens Axboe