linux-hardening - Re: [PATCH] fortify: Avoid shadowing previous locals

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Date:   Mon, 25 Oct 2021 16:15:28 -0400
From:   Qian Cai <quic_qiancai@...cinc.com>
To:     Kees Cook <keescook@...omium.org>
CC:     <linux-hardening@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fortify: Avoid shadowing previous locals



On 10/25/21 3:34 PM, Kees Cook wrote:
> On Mon, Oct 25, 2021 at 02:37:28PM -0400, Qian Cai wrote:
>> __compiletime_strlen macro expansion will shadow p_size and p_len local
>> variables. Just rename those in __compiletime_strlen.
> 
> They don't escape their local context, though, right? i.e. I don't see a
> problem with the existing macro. Did you encounter a specific issue that
> this patch fixes?

Yes, this is pretty minor. There are also some extra compiling warnings (W=2)
from it.

./include/linux/fortify-string.h: In function 'strnlen':

./include/linux/fortify-string.h:17:9: warning: declaration of 'p_size' shadows a previous local [-Wshadow]

   17 |  size_t p_size = __builtin_object_size(p, 1); \

      |         ^~~~~~

./include/linux/fortify-string.h:77:17: note: in expansion of macro '__compiletime_strlen'
   77 |  size_t p_len = __compiletime_strlen(p);

      |                 ^~~~~~~~~~~~~~~~~~~~

./include/linux/fortify-string.h:76:9: note: shadowed declaration is here

   76 |  size_t p_size = __builtin_object_size(p, 1);

      |         ^~~~~~

./include/linux/fortify-string.h:19:10: warning: declaration of 'p_len' shadows a previous local [-Wshadow]

   19 |   size_t p_len = p_size - 1;  \

      |          ^~~~~

./include/linux/fortify-string.h:77:17: note: in expansion of macro '__compiletime_strlen'
   77 |  size_t p_len = __compiletime_strlen(p);

      |                 ^~~~~~~~~~~~~~~~~~~~

./include/linux/fortify-string.h:77:9: note: shadowed declaration is here

   77 |  size_t p_len = __compiletime_strlen(p);

      |         ^~~~~