Re: [PATCH] [v2] scsi: ipr: work around fortify-string warning

[Kees Cook <keescook@chromium.org>]

On Tue, Feb 14, 2023 at 02:28:08PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The ipr_log_vpd_compact() function triggers a fortified memcpy() warning
> about a potential string overflow with all versions of clang:
> 
> In file included from drivers/scsi/ipr.c:43:
> In file included from include/linux/string.h:254:
> include/linux/fortify-string.h:520:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
>                         __write_overflow_field(p_size_field, size);
>                         ^
> include/linux/fortify-string.h:520:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
> 2 errors generated.
> 
> I don't see anything actually wrong with the function, but this is the
> only instance I can reproduce of the fortification going wrong in the
> kernel at the moment, so the easiest solution may be to rewrite the
> function into something that does not trigger the warning.
> 
> Instead of having a combined buffer for vendor/device/serial strings,
> use three separate local variables and just truncate the whitespace
> individually.
> 
> Fixes: 8cf093e275d0 ("[SCSI] ipr: Improved dual adapter errors")
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

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

Reproduced this locally -- I agree your fix looks like the best
approach. I think Clang was seeing the old "i + 2" return as potentially
overflowing in the case where there was no space-padding on any strings.

-- 
Kees Cook