linux-kernel - Re: [PATCH] net: mvpp2: replace deprecated strncpy with strscpy

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Message-ID: <202310101658.8D498F16F@keescook>
Date:   Tue, 10 Oct 2023 16:59:10 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] net: mvpp2: replace deprecated strncpy with strscpy

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: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Yup, direct replacement.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook