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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Tue, 16 Mar 2021 17:03:28 +0100
Message-ID: <CAK8P3a3A=TVWWmog=1YsALUhsaSkqReNrao5OTRd5mwyd0pnig@mail.gmail.com>
Subject: Re: [syzbot] kernel panic: corrupted stack end in openat
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        syzbot <syzbot+0b06ef9b44d00d600183@syzkaller.appspotmail.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>
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On Tue, Mar 16, 2021 at 4:51 PM Russell King - ARM Linux admin
<linux@armlinux.org.uk> wrote:
> On Tue, Mar 16, 2021 at 04:44:45PM +0100, Arnd Bergmann wrote:
> > On Tue, Mar 16, 2021 at 11:17 AM Dmitry Vyukov <dvyukov@google.com> wrote:
> > > The compiler is gcc version 10.2.1 20210110 (Debian 10.2.1-6)
> >
> > Ok, building with Ubuntu 10.2.1-1ubuntu1 20201207 locally, that's
> > the closest I have installed, and I think the Debian and Ubuntu versions
> > are generally quite close in case of gcc since they are maintained by
> > the same packagers.
>
> ... which shouldn't be a problem - that's just over 1/4 of the stack
> space. Could it be the syzbot's gcc is doing something weird and
> inflating the stack frames?

It's possible, I think that's really unlikely given that it's just Debian's
gcc, which is as close to mainline as the version I was using.

Uwe's DEBUG_STACKOVERFLOW patch from a while ago might
help if this was the problem though:
https://lore.kernel.org/linux-arm-kernel/20200108082913.29710-1-u.kleine-koenig@pengutronix.de/

My best guess is something going wrong in the interrupt
that triggered the preempt_schedule() which ended up calling
task_stack_end_corrupted() in schedule_debug(), as you suggested
earlier.

       Arnd