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Date:   Tue, 27 Dec 2022 19:40:30 -0800
From:   Kees Cook <kees@kernel.org>
To:     Guenter Roeck <linux@roeck-us.net>
CC:     Linus Torvalds <torvalds@linux-foundation.org>,
        Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Kees Cook <keescook@chromium.org>
Subject: Re: Linux 6.2-rc1
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On December 26, 2022 9:52:12 PM PST, Guenter Roeck <linux@roeck-us=2Enet> w=
rote:
>On Mon, Dec 26, 2022 at 05:32:28PM -0800, Kees Cook wrote:
>> On December 26, 2022 4:29:41 PM PST, Guenter Roeck <linux@roeck-us=2Ene=
t> wrote:
>> >On Mon, Dec 26, 2022 at 01:03:59PM -0800, Kees Cook wrote:
>> >> On December 26, 2022 12:56:29 PM PST, Linus Torvalds <torvalds@linux=
-foundation=2Eorg> wrote:
>> >> >On Mon, Dec 26, 2022 at 11:52 AM Guenter Roeck <linux@roeck-us=2Ene=
t> wrote:
>> >> >>
>> >> >> fs/f2fs/inline=2Ec: In function 'f2fs_move_inline_dirents':
>> >> >> include/linux/fortify-string=2Eh:59:33: error: '__builtin_memset'=
 pointer overflow between offset [28, 898293814] and size [-898293787, -1] =
[-Werror=3Darray-bounds]
>> >> >> fs/f2fs/inline=2Ec:430:9: note: in expansion of macro 'memset'
>> >> >>   430 |         memset(dst=2Ebitmap + src=2Enr_bitmap, 0, dst=2En=
r_bitmap - src=2Enr_bitmap);
>> >> >>       |         ^~~~~~
>> >> >
>> >> >Well, that's unfortunate=2E
>> >>=20
>> >> I'll look into this=2E
>> >>=20
>> >
>> >I did some more testing=2E The problem is seen with gcc 11=2E3=2E0, bu=
t not with
>> >gcc 12=2E2=2E0 nor with gcc 10=2E3=2E0=2E
>>=20
>> That's what I'd expect: 10 didn't have variable range tracking wired up=
 to -Warray-bounds, 11 does, and we disable -Warray-bounds on 12 because of=
 3 separate 12-only GCC bugs=2E
>>=20
>> > gcc bug ? Should I switch to gcc 12=2E2=2E0 for
>> >powerpc when build testing the latest kernel ?
>>=20
>> Sure? But that'll just hide it=2E I suspect GCC has found a way for dst=
=2Enr_bitmap to be compile-time 27, so the size is always negative=2E
>>=20
>dst=2Enr_bitmap is initialized with SIZE_OF_DENTRY_BITMAP,
>which is defined as:
>
>#define NR_DENTRY_IN_BLOCK      214     /* the number of dentry in a bloc=
k */
>#define SIZE_OF_DIR_ENTRY       11      /* by byte */
>#define SIZE_OF_DENTRY_BITMAP   ((NR_DENTRY_IN_BLOCK + BITS_PER_BYTE - 1)=
 / \
>                                        BITS_PER_BYTE)
>
>((214 + 8 - 1) / 8 =3D 27, so dst=2Enr_bitmap is indeed compile-time 27=
=2E
>
>Not sure how would know that src=2Enr_bitmap can be > 27, though=2E
>Am I missing something ?

I think it's saying it can't rule out it being larger? I=2Ee=2E there is n=
o obvious bounds checking for it=2E Perhaps:

if (src=2Enr_bitmap > dst=2Enr_bitmap) {
    err =3D -EFSCORRUPTED;
		goto out;
}


-Kees


--=20
Kees Cook