Re: [PATCH-for-7.2 v2] libvduse: Avoid warning about dangerous use of strncpy()

[Bin Meng]

> From: Philippe Mathieu-Daudé <f4bug@amsat.org>
> 
> GCC 8 added a -Wstringop-truncation warning:
> 
>   The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
>   bug 81117 is specifically intended to highlight likely unintended
>   uses of the strncpy function that truncate the terminating NUL
>   character from the source string.
> 
> Here the next line indeed unconditionally zeroes the last byte, but
> 1/ the buffer has been calloc'd, so we don't need to add an extra
> byte, and 2/ we called vduse_name_is_invalid() which checked the
> string length, so we can simply call strcpy().
> 
> This fixes when using gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0:
> 
>   [42/666] Compiling C object subprojects/libvduse/libvduse.a.p/libvduse.c.o
>   FAILED: subprojects/libvduse/libvduse.a.p/libvduse.c.o
>   cc -m64 -mcx16 -Isubprojects/libvduse/libvduse.a.p -Isubprojects/libvduse 
> -I../../subprojects/libvduse [...] -o 
> subprojects/libvduse/libvduse.a.p/libvduse.c.o -c 
> ../../subprojects/libvduse/libvduse.c
>   In file included from /usr/include/string.h:495,
>                    from ../../subprojects/libvduse/libvduse.c:24:
>   In function ‘strncpy’,
>       inlined from ‘vduse_dev_create’ at 
> ../../subprojects/libvduse/libvduse.c:1312:5:
>   /usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error: 
> ‘__builtin_strncpy’ specified bound 256 equals destination size 
> [-Werror=stringop-truncation]
>     106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos 
> (__dest));
>         |          
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   cc1: all warnings being treated as errors
>   ninja: build stopped: cannot make progress due to previous errors.
> 
> Fixes: d9cf16c0be ("libvduse: Replace strcpy() with strncpy()")
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
> Supersedes: <20220919192306.52729-1-f4bug@amsat.org>
> Cc: Xie Yongji <xieyongji@bytedance.com>
> Cc: Kevin Wolf <kwolf@redhat.com>
> ---
>  subprojects/libvduse/libvduse.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Tested-by: Bin Meng <bmeng@tinylab.org>