linux-hardening - Re: [PATCH] drm/etnaviv: refactor deprecated strncpy

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Date:   Thu, 14 Sep 2023 21:33:25 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Lucas Stach <l.stach@...gutronix.de>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, etnaviv@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, Bo YU <tsu.yubo@...il.com>
Subject: Re: [PATCH] drm/etnaviv: refactor deprecated strncpy

On Thu, Sep 14, 2023 at 06:20:01PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it guarantees
> NUL-termination on the destination buffer.
> 
> 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
> Cc: Bo YU <tsu.yubo@...il.com>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Similar to [1] which was never picked up. Let's prefer strscpy to strlcpy, though
> 
> [1]: https://lore.kernel.org/all/20190328080918.9290-1-tsu.yubo@gmail.com/
> ---
>  drivers/gpu/drm/etnaviv/etnaviv_perfmon.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_perfmon.c b/drivers/gpu/drm/etnaviv/etnaviv_perfmon.c
> index bafdfe49c1d8..9e7bebcf24eb 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_perfmon.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_perfmon.c
> @@ -511,7 +511,7 @@ int etnaviv_pm_query_dom(struct etnaviv_gpu *gpu,
>  
>  	domain->id = domain->iter;
>  	domain->nr_signals = dom->nr_signals;
> -	strncpy(domain->name, dom->name, sizeof(domain->name));
> +	strscpy(domain->name, dom->name, sizeof(domain->name));

It looks like this is passing through an ioctl(). Let's use
strscpy_pad(0 instead...

-Kees

>  
>  	domain->iter++;
>  	if (domain->iter == nr_domains)
> @@ -540,7 +540,7 @@ int etnaviv_pm_query_sig(struct etnaviv_gpu *gpu,
>  	sig = &dom->signal[signal->iter];
>  
>  	signal->id = signal->iter;
> -	strncpy(signal->name, sig->name, sizeof(signal->name));
> +	strscpy(signal->name, sig->name, sizeof(signal->name));
>  
>  	signal->iter++;
>  	if (signal->iter == dom->nr_signals)
> 
> ---
> base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
> change-id: 20230914-strncpy-drivers-gpu-drm-etnaviv-etnaviv_perfmon-c-dd095491dfde
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 

-- 
Kees Cook