Subject: Re: [PATCH] net: mvpp2: replace deprecated strncpy with strscpy

From: Kees Cook <[email-masked]>
Date: Tue, 10 Oct 2023 16:59:10 -0700

On Tue, Oct 10, 2023 at 09:24:42PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> We expect `irqname` to be NUL-terminated based on its use with
> of_irq_get_byname() -> of_property_match_string() wherein it is used
> with a format string and a `strcmp`:
> |       pr_debug("comparing %s with %s\n", string, p);
> |       if (strcmp(string, p) == 0)
> |               return i; /* Found it; return index */
> 
> NUL-padding is not required as is evident by other assignments to
> `irqname` which do not NUL-pad:
> |       if (port->flags & MVPP2_F_DT_COMPAT)
> |               snprintf(irqname, sizeof(irqname), "tx-cpu%d", i);
> |       else
> |               snprintf(irqname, sizeof(irqname), "hif%d", i);
> 
> Considering the above, a suitable replacement is `strscpy` [2] due to
> the fact that it guarantees NUL-termination on the destination buffer
> without unnecessarily NUL-padding.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: [email-masked]
> Signed-off-by: Justin Stitt <[email-masked]>

Yup, direct replacement.

Reviewed-by: Kees Cook <[email-masked]>

-- 
Kees Cook