Re: [PATCH net-next] net/rds: Replace deprecated strncpy() with strscpy_pad()

[Kees Cook <kees@kernel.org>]

On Wed, Feb 19, 2025 at 11:47:31PM +0100, Thorsten Blum wrote:
> strncpy() is deprecated for NUL-terminated destination buffers. Use
> strscpy_pad() instead and remove the manual NUL-termination.

When doing these conversions, please describe two aspects of
conversions:

- Why is it safe to be NUL terminated
- Why is it safe to be/not-be NUL-padded

In this case, the latter needs examination. Looking at how ctr is used,
it is memcpy()ed later, which means this string MUST be NUL padded or it
will leak stack memory contents.

So, please use strscpy_pad() here. :)

-Kees

> 
> Compile-tested only.
> 
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
>  net/rds/stats.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/net/rds/stats.c b/net/rds/stats.c
> index 9e87da43c004..cb2e3d2cdf73 100644
> --- a/net/rds/stats.c
> +++ b/net/rds/stats.c
> @@ -89,8 +89,7 @@ void rds_stats_info_copy(struct rds_info_iterator *iter,
>  
>  	for (i = 0; i < nr; i++) {
>  		BUG_ON(strlen(names[i]) >= sizeof(ctr.name));
> -		strncpy(ctr.name, names[i], sizeof(ctr.name) - 1);
> -		ctr.name[sizeof(ctr.name) - 1] = '\0';
> +		strscpy_pad(ctr.name, names[i]);
>  		ctr.value = values[i];
>  
>  		rds_info_copy(iter, &ctr, sizeof(ctr));
> -- 
> 2.48.1
> 
> 

-- 
Kees Cook