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Date:   Tue, 16 Mar 2021 15:51:02 +0000
From:   Russell King - ARM Linux admin <linux@armlinux.org.uk>
To:     Arnd Bergmann <arnd@arndb.de>
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>
Subject: Re: [syzbot] kernel panic: corrupted stack end in openat
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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:
> > On Tue, Mar 16, 2021 at 11:02 AM Arnd Bergmann <arnd@arndb.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?

-- 
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