Re: [syzbot] KASAN: use-after-free Read in blk_mq_sched_tags_teardown

[John Garry]

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@xxxxxxxxxx>
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> 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()