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Date:   Tue, 10 Oct 2023 17:01:19 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     Sunil Goutham <sgoutham@marvell.com>,
        Linu Cherian <lcherian@marvell.com>,
        Geetha sowjanya <gakula@marvell.com>,
        Jerin Jacob <jerinj@marvell.com>,
        hariprasad <hkelam@marvell.com>,
        Subbaraya Sundeep <sbhatta@marvell.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] octeontx2-af: replace deprecated strncpy with strscpy
Message-ID: <202310101700.1BE3455BE6@keescook>
References: <20231010-strncpy-drivers-net-ethernet-marvell-octeontx2-af-cgx-c-v1-1-a443e18f9de8@google.com>
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In-Reply-To: <20231010-strncpy-drivers-net-ethernet-marvell-octeontx2-af-cgx-c-v1-1-a443e18f9de8@google.com>
Precedence: bulk

On Tue, Oct 10, 2023 at 09:38:11PM +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 can see that linfo->lmac_type is expected to be NUL-terminated based
> on the `... - 1`'s present in the current code. Presumably making room
> for a NUL-byte at the end of the buffer.
> 
> 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.
> 
> Let's also prefer the more idiomatic strscpy usage of (dest, src,
> sizeof(dest)) rather than (dest, src, SOME_LEN).
> 
> 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@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Note: build-tested only.
> ---
>  drivers/net/ethernet/marvell/octeontx2/af/cgx.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/octeontx2/af/cgx.c b/drivers/net/ethernet/marvell/octeontx2/af/cgx.c
> index e06f77ad6106..6c70c8498690 100644
> --- a/drivers/net/ethernet/marvell/octeontx2/af/cgx.c
> +++ b/drivers/net/ethernet/marvell/octeontx2/af/cgx.c
> @@ -1218,8 +1218,6 @@ static inline void link_status_user_format(u64 lstat,
>  					   struct cgx_link_user_info *linfo,
>  					   struct cgx *cgx, u8 lmac_id)
>  {
> -	const char *lmac_string;
> -
>  	linfo->link_up = FIELD_GET(RESP_LINKSTAT_UP, lstat);
>  	linfo->full_duplex = FIELD_GET(RESP_LINKSTAT_FDUPLEX, lstat);
>  	linfo->speed = cgx_speed_mbps[FIELD_GET(RESP_LINKSTAT_SPEED, lstat)];
> @@ -1230,12 +1228,12 @@ static inline void link_status_user_format(u64 lstat,
>  	if (linfo->lmac_type_id >= LMAC_MODE_MAX) {
>  		dev_err(&cgx->pdev->dev, "Unknown lmac_type_id %d reported by firmware on cgx port%d:%d",
>  			linfo->lmac_type_id, cgx->cgx_id, lmac_id);
> -		strncpy(linfo->lmac_type, "Unknown", LMACTYPE_STR_LEN - 1);
> +		strscpy(linfo->lmac_type, "Unknown", sizeof(linfo->lmac_type));
>  		return;
>  	}
>  
> -	lmac_string = cgx_lmactype_string[linfo->lmac_type_id];
> -	strncpy(linfo->lmac_type, lmac_string, LMACTYPE_STR_LEN - 1);
> +	strscpy(linfo->lmac_type, cgx_lmactype_string[linfo->lmac_type_id],
> +		sizeof(linfo->lmac_type));

Yup, sizes match. Good replacement and simplification.

drivers/net/ethernet/marvell/octeontx2/af/mbox.h:565:#define LMACTYPE_STR_LEN 16
drivers/net/ethernet/marvell/octeontx2/af/mbox.h:566:   char lmac_type[LMACTYPE_STR_LEN];

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

-- 
Kees Cook