Re: [PATCH] octeontx2-af: replace deprecated strncpy with strscpy

Kees Cook
2023-10-11T00:01:28Z

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>

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Kees Cook