Re: [PATCH v2 2/2] kobject: Fix -Wstringop-truncation warning

[Christophe LEROY]

Le 25/06/2018 Ã 14:45, Stafford Horne a ÃcritÂ:
> When compiling with GCC 9.0.0 I am seeing the following warning:
>
>      In function âfill_kobj_pathâ,
> 	inlined from âkobject_get_pathâ at lib/kobject.c:155:2:
>      lib/kobject.c:128:3: warning: âstrncpyâ output truncated before terminating nul copying as many bytes from a string as its length [-Wstringop-truncation]
>         strncpy(path + length, kobject_name(parent), cur);
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>      lib/kobject.c: In function âkobject_get_pathâ:
>      lib/kobject.c:125:13: note: length computed here
>         int cur = strlen(kobject_name(parent));
> 		 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> This is not really an issue since the buffer we are writing to is
> pre-zero'd and we have already allocated the buffer based on the
> calculated strlen size and accounted for the terminating '\0'.
> Just use memcpy() instead.

If we are already sure the destination is big enough, why not just do a 
strcpy() and drop the 'cur = strlen()' ?

Christophe

> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Eric Biggers <ebiggers3@xxxxxxxxx>
> Signed-off-by: Stafford Horne <shorne@xxxxxxxxx>
> ---
>   lib/kobject.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/kobject.c b/lib/kobject.c
> index 18989b5b3b56..e876957743c8 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -125,7 +125,7 @@ static void fill_kobj_path(struct kobject *kobj, char *path, int length)
>   		int cur = strlen(kobject_name(parent));
>   		/* back up enough to print this name with '/' */
>   		length -= cur;
> -		strncpy(path + length, kobject_name(parent), cur);
> +		memcpy(path + length, kobject_name(parent), cur);
>   		*(path + --length) = '/';
>   	}
>