linux-kernel - Re: WARNING in arch_install_hw

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Date:   Mon, 9 Dec 2019 16:10:13 -0800
From:   Kees Cook <keescook@...omium.org>
To:     syzbot <syzbot+370a6b0f11867bf13515@...kaller.appspotmail.com>
Cc:     acme@...nel.org, akpm@...ux-foundation.org, arnd@...db.de,
        bp@...en8.de, bp@...e.de, christian@...uner.io, cyphar@...har.com,
        dhowells@...hat.com, dvyukov@...gle.com, ebiederm@...ssion.com,
        frederic@...nel.org, gustavo@...eddedor.com, hpa@...or.com,
        jannh@...gle.com, jolsa@...hat.com, linux-kernel@...r.kernel.org,
        luto@...nel.org, mark.rutland@....com, mhiramat@...nel.org,
        mingo@...nel.org, mingo@...hat.com, mtk.manpages@...il.com,
        namhyung@...nel.org, oleg@...hat.com, peterz@...radead.org,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
        torvalds@...ux-foundation.org, viro@...iv.linux.org.uk,
        x86@...nel.org
Subject: Re: WARNING in arch_install_hw_breakpoint

On Sun, Dec 08, 2019 at 07:33:00AM -0800, syzbot wrote:
> syzbot suspects this bug was fixed by commit:
> 
> commit b3e5838252665ee4cfa76b82bdf1198dca81e5be
> Author: Christian Brauner <christian@...uner.io>
> Date:   Wed Mar 27 12:04:15 2019 +0000
> 
>     clone: add CLONE_PIDFD

That seems ... unlikely? I suspect this WARN should just be pr_err or
something:

        if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
                return -EBUSY;

If it's reachable through normal code, it shouldn't be possible to trip
a WARN.

-Kees

> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1268377ae00000
> start commit:   fd1f297b Merge tag 'drm-fixes-2019-03-22' of git://anongit..
> git tree:       upstream
> kernel config:  https://syzkaller.appspot.com/x/.config?x=9a31fb246de2a622
> dashboard link: https://syzkaller.appspot.com/bug?extid=370a6b0f11867bf13515
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15d8bd93200000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15439f27200000
> 
> If the result looks correct, please mark the bug fixed by replying with:
> 
> #syz fix: clone: add CLONE_PIDFD
> 
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

-- 
Kees Cook