netdev - Re: [PATCH v3] netfilter: ebtables: fix fortify warnings in size_entry

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Date: Thu, 10 Aug 2023 13:21:25 -0700
From: Kees Cook <keescook@...omium.org>
To: "GONG, Ruiqi" <gongruiqi@...weicloud.com>
Cc: Pablo Neira Ayuso <pablo@...filter.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>,
	Florian Westphal <fw@...len.de>, Roopa Prabhu <roopa@...dia.com>,
	Nikolay Aleksandrov <razor@...ckwall.org>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org, linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Wang Weiyang <wangweiyang2@...wei.com>,
	Xiu Jianfeng <xiujianfeng@...wei.com>, gongruiqi1@...wei.com
Subject: Re: [PATCH v3] netfilter: ebtables: fix fortify warnings in
 size_entry_mwt()

On Wed, Aug 09, 2023 at 03:45:03PM +0800, GONG, Ruiqi wrote:
> From: "GONG, Ruiqi" <gongruiqi1@...wei.com>
> 
> When compiling with gcc 13 and CONFIG_FORTIFY_SOURCE=y, the following
> warning appears:
> 
> In function ‘fortify_memcpy_chk’,
>     inlined from ‘size_entry_mwt’ at net/bridge/netfilter/ebtables.c:2118:2:
> ./include/linux/fortify-string.h:592:25: error: call to ‘__read_overflow2_field’
> declared with attribute warning: detected read beyond size of field (2nd parameter);
> maybe use struct_group()? [-Werror=attribute-warning]
>   592 |                         __read_overflow2_field(q_size_field, size);
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The compiler is complaining:
> 
> memcpy(&offsets[1], &entry->watchers_offset,
>                        sizeof(offsets) - sizeof(offsets[0]));
> 
> where memcpy reads beyong &entry->watchers_offset to copy
> {watchers,target,next}_offset altogether into offsets[]. Silence the
> warning by wrapping these three up via struct_group().
> 
> Signed-off-by: GONG, Ruiqi <gongruiqi1@...wei.com>

If a v4 is sent, please fix the "beyong" typo that was pointed out.
Otherwise, it looks okay to me:

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

-- 
Kees Cook