linux-kernel - Re: [syzbot] KASAN: use-after-free Read in blk_mq_sched_tags

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Date:   Mon, 25 Oct 2021 10:46:51 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     John Garry <john.garry@...wei.com>
Cc:     syzbot <syzbot+412ca156285f619b8b62@...kaller.appspotmail.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "hare@...e.de" <hare@...e.de>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] KASAN: use-after-free Read in blk_mq_sched_tags_teardown

On Mon, 25 Oct 2021 at 10:39, John Garry <john.garry@...wei.com> wrote:
>
> On 25/10/2021 02:35, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    51dba6e335ff Add linux-next specific files for 20211020
> > git tree:       linux-next
> > console output:https://syzkaller.appspot.com/x/log.txt?x=10171dc8b00000
> > kernel config:https://syzkaller.appspot.com/x/.config?x=1adca843ed814d57
> > dashboard link:https://syzkaller.appspot.com/bug?extid=412ca156285f619b8b62
> > 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=14f768b4b00000
> > C reproducer:https://syzkaller.appspot.com/x/repro.c?x=1295a8c7300000
> >
> > The issue was bisected to:
> >
> > commit 645db34e50501aac141713fb47a315e5202ff890
>
> I think that it should be e155b0c238b2 ("blk-mq: Use shared tags for
> shared sbitmap support")
>
> > Author: John Garry<john.garry@...wei.com>
> > Date:   Tue Oct 5 10:23:36 2021 +0000
> >
> >      blk-mq: Refactor and rename blk_mq_free_map_and_{requests->rqs}()
> >
> > bisection log:https://syzkaller.appspot.com/x/bisect.txt?x=1597e130b00000
> > final oops:https://syzkaller.appspot.com/x/report.txt?x=1797e130b00000
> > console output:https://syzkaller.appspot.com/x/log.txt?x=1397e130b00000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by:syzbot+412ca156285f619b8b62@...kaller.appspotmail.com
> > Fixes: 645db34e5050 ("blk-mq: Refactor and rename blk_mq_free_map_and_{requests->rqs}()")
> >
> > ==================================================================
> > BUG: KASAN: use-after-free in blk_mq_sched_tags_teardown+0x2a1/0x2d0 block/blk-mq-sched.c:544
> > Read of size 4 at addr ffff8880760b81e0 by task systemd-udevd/6750
>
> #syz fix: blk-mq-sched: Don't reference queue tagset in
> blk_mq_sched_tags_teardown()

Hi John,

Thanks for updating the bug.
It looks like the title was line wrapped. There is a hack specifically
for gmail to put the title onto separate line, it's still parsable
this way (if the whole title fits into 78 cols of course :))

#syz fix:
blk-mq-sched: Don't reference queue tagset in blk_mq_sched_tags_teardown()