Re: [Qemu-devel] [PATCH v2 1/5] linux-user: avoid string truncation warnings in uname field copying

[Laurent Vivier <laurent@vivier.eu>]

On 12/04/2019 14:16, Daniel P. Berrangé wrote:
> In file included from /usr/include/string.h:494,
>                  from include/qemu/osdep.h:101,
>                  from linux-user/uname.c:20:
> In function ‘strncpy’,
>     inlined from ‘sys_uname’ at linux-user/uname.c:94:3:
> /usr/include/bits/string_fortified.h:106:10: warning: ‘__builtin_strncpy’ output may be truncated copying 64 bytes from a string of length 64 [-Wstringop-truncation]
>   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> We don't care where the NUL terminator in the original uname
> field was. It suffices to copy the entire original field and
> simply force a NUL terminator at the end of the new field.
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  linux-user/uname.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/linux-user/uname.c b/linux-user/uname.c
> index 313b79dbad..3dff33effe 100644
> --- a/linux-user/uname.c
> +++ b/linux-user/uname.c
> @@ -73,7 +73,7 @@ const char *cpu_to_uname_machine(void *cpu_env)
>  #define COPY_UTSNAME_FIELD(dest, src) \
>    do { \
>        /* __NEW_UTS_LEN doesn't include terminating null */ \
> -      (void) strncpy((dest), (src), __NEW_UTS_LEN); \
> +      memcpy((dest), (src), MIN(sizeof(src), __NEW_UTS_LEN));   \

If we use sizeof(), I think we should use it for both:

  MIN(sizeof(dest), sizeof(src))

Thanks,
Laurent