linux-kernel - Re: [syzbot] kernel panic: corrupted stack end in openat

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Date:   Tue, 16 Mar 2021 17:03:16 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Arnd Bergmann <arnd@...db.de>,
        syzbot <syzbot+0b06ef9b44d00d600183@...kaller.appspotmail.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] kernel panic: corrupted stack end in openat

On Tue, Mar 16, 2021 at 4:51 PM Russell King - ARM Linux admin
<linux@...linux.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@...gle.com> wrote:
> > > On Tue, Mar 16, 2021 at 11:02 AM Arnd Bergmann <arnd@...db.de> wrote:
> > > > > On Tue, Mar 16, 2021 at 8:18 AM syzbot
> > >
> > > > > > [<8073772c>] (integrity_kernel_read) from [<8073a904>] (ima_calc_file_hash_tfm+0x178/0x228 security/integrity/ima/ima_crypto.c:484)
> > > > > > [<8073a78c>] (ima_calc_file_hash_tfm) from [<8073ae2c>] (ima_calc_file_shash security/integrity/ima/ima_crypto.c:515 [inline])
> > > > > > [<8073a78c>] (ima_calc_file_hash_tfm) from [<8073ae2c>] (ima_calc_file_hash+0x124/0x8b8 security/integrity/ima/ima_crypto.c:572)
> > > >
> > > > ima_calc_file_hash_tfm() has a SHASH_DESC_ON_STACK(), which by itself can
> > > > use up 512 bytes, but KASAN sometimes triples this number. However, I see
> > > > you do not actually have KASAN enabled, so there is probably more to it.
> > >
> > > 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.
> >
> > I see ima_calc_field_array_hash_tfm() shows up as one of the larger
> > stack users, but not alarmingly high:
> > ../security/integrity/ima/ima_crypto.c: In function
> > ‘ima_calc_field_array_hash_tfm’:
> > ../security/integrity/ima/ima_crypto.c:624:1: warning: the frame size
> > of 664 bytes is larger than 600 bytes [-Wframe-larger-than=]
> > none of the other functions from the call chain have more than 600 bytes
> > in this combination of config/compiler/sourcetree.
> >
> > In combination, I don't get to more than ~2300 bytes:
>
> ... 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 just a stock Debian-provided gcc. Which I would assume also just
a plain gcc.