linux-hardening - Re: [PATCH 5.17-rc1 v2] eeprom: at25: Restore missing allocation

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Date:   Tue, 25 Jan 2022 09:43:29 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Jiri Prchal <jiri.prchal@...ignal.cz>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Ralph Siemsen <ralph.siemsen@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 5.17-rc1 v2] eeprom: at25: Restore missing allocation

On Tue, Jan 25, 2022 at 04:25:39PM +0100, Geert Uytterhoeven wrote:
> On Tue, Jan 25, 2022 at 3:20 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Fri, Jan 21, 2022 at 12:33 AM Kees Cook <keescook@...omium.org> wrote:
> > > The at25 driver regressed in v5.17-rc1 due to a broken conflict
> > > resolution: the allocation of the object was accidentally removed. Restore
> > > it.
> > >
> > > This was found when building under CONFIG_FORTIFY_SOURCE=y and
> > > -Warray-bounds, which complained about strncpy() being used against an
> > > empty object:
> > >
> > > In function 'strncpy',
> > >     inlined from 'at25_fw_to_chip.constprop' at drivers/misc/eeprom/at25.c:312:2:
> > > ./include/linux/fortify-string.h:48:33: warning: '__builtin_strncpy' offset [0, 9] is out of the bounds [0, 0] [-Warray-bounds]
> > >    48 | #define __underlying_strncpy    __builtin_strncpy
> > >       |                                 ^
> > > ./include/linux/fortify-string.h:59:16: note: in expansion of macro '__underlying_strncpy'
> > >    59 |         return __underlying_strncpy(p, q, size);
> > >       |                ^~~~~~~~~~~~~~~~~~~~
> > > In function 'strncpy',
> > >     inlined from 'at25_fram_to_chip' at drivers/misc/eeprom/at25.c:373:2,
> > >     inlined from 'at25_probe' at drivers/misc/eeprom/at25.c:453:10:
> > > ./include/linux/fortify-string.h:48:33: warning: '__builtin_strncpy' offset [0, 9] is out of the bounds [0, 0] [-Warray-bounds]
> > >    48 | #define __underlying_strncpy    __builtin_strncpy
> > >       |                                 ^
> > > ./include/linux/fortify-string.h:59:16: note: in expansion of macro '__underlying_strncpy'
> > >    59 |         return __underlying_strncpy(p, q, size);
> > >       |                ^~~~~~~~~~~~~~~~~~~~
> >
> > On real hardware:
> >
> >     Unable to handle kernel access to user memory outside uaccess
> > routines at virtual address 0000000000000028
> >     ...
> >     pc : __mutex_init+0x20/0x68
> >     lr : at25_probe+0x8c/0x4d8
> 
> To avoid confusion: of course the crash happens only without Kees'
> patch.  I just wanted to point out what happens when you boot on
> real hardware, as it might be worthwhile to add that to the commit
> description.

Okay, whew. :)


-- 
Kees Cook