linux-kernel - Re: [PATCH][next] firewire: Replace zero-length array with flexible-array member

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Message-ID: <202305301608.741EEDDD@keescook>
Date:   Tue, 30 May 2023 16:09:00 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Takashi Sakamoto <o-takashi@...amocchi.jp>,
        linux1394-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] firewire: Replace zero-length array with
 flexible-array member

On Mon, May 29, 2023 at 12:52:07PM -0600, Gustavo A. R. Silva wrote:
> Zero-length and one-element arrays are deprecated, and we are moving
> towards adopting C99 flexible-array members, instead.
> 
> Address the following warnings found with GCC-13 and
> -fstrict-flex-arrays=3 enabled:
> sound/firewire/amdtp-stream.c: In function ‘build_it_pkt_header’:
> sound/firewire/amdtp-stream.c:694:17: warning: ‘generate_cip_header’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
>   694 |                 generate_cip_header(s, cip_header, data_block_counter, syt);
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> sound/firewire/amdtp-stream.c:694:17: note: referencing argument 2 of type ‘__be32[2]’ {aka ‘unsigned int[2]’}
> sound/firewire/amdtp-stream.c:667:13: note: in a call to function ‘generate_cip_header’
>   667 | static void generate_cip_header(struct amdtp_stream *s, __be32 cip_header[2],
>       |             ^~~~~~~~~~~~~~~~~~~
> 
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> routines on memcpy() and help us make progress towards globally
> enabling -fstrict-flex-arrays=3 [1].
> 
> Link: https://github.com/KSPP/linux/issues/21
> Link: https://github.com/KSPP/linux/issues/303
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook