[PATCH] sfc: replace deprecated strncpy with strscpy

[PATCH] sfc: replace deprecated strncpy with strscpy

[Justin Stitt]

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

`desc` is expected to be NUL-terminated as evident by the manual
NUL-byte assignment. Moreover, NUL-padding does not seem to be
necessary.

The only caller of efx_mcdi_nvram_metadata() is
efx_devlink_info_nvram_partition() which provides a NULL for `desc`:
|       rc = efx_mcdi_nvram_metadata(efx, partition_type, NULL, version, NULL, 0);

Due to this, I am not sure this code is even reached but we should still
favor something other than strncpy.

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@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/net/ethernet/sfc/mcdi.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/sfc/mcdi.c b/drivers/net/ethernet/sfc/mcdi.c
index d23da9627338..76578502226e 100644
--- a/drivers/net/ethernet/sfc/mcdi.c
+++ b/drivers/net/ethernet/sfc/mcdi.c
@@ -2205,10 +2205,9 @@ int efx_mcdi_nvram_metadata(struct efx_nic *efx, unsigned int type,
 				goto out_free;
 			}
 
-			strncpy(desc,
+			strscpy(desc,
 				MCDI_PTR(outbuf, NVRAM_METADATA_OUT_DESCRIPTION),
 				MC_CMD_NVRAM_METADATA_OUT_DESCRIPTION_NUM(outlen));
-			desc[MC_CMD_NVRAM_METADATA_OUT_DESCRIPTION_NUM(outlen)] = '\0';
 		} else {
 			desc[0] = '\0';
 		}

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231012-strncpy-drivers-net-ethernet-sfc-mcdi-c-cf970a9b7d60

Best regards,
--
Justin Stitt <justinstitt@google.com>

Re: [PATCH] sfc: replace deprecated strncpy with strscpy

[Edward Cree]

On 12/10/2023 21:38, 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.
> 
> `desc` is expected to be NUL-terminated as evident by the manual
> NUL-byte assignment. Moreover, NUL-padding does not seem to be
> necessary.
> 
> The only caller of efx_mcdi_nvram_metadata() is
> efx_devlink_info_nvram_partition() which provides a NULL for `desc`:
> |       rc = efx_mcdi_nvram_metadata(efx, partition_type, NULL, version, NULL, 0);
> 
> Due to this, I am not sure this code is even reached but we should still
> favor something other than strncpy.
> 
> 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@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Acked-by: Edward Cree <ecree.xilinx@gmail.com>
but ideally we should just rip out the dead code instead.  If this
 patch gets taken as-is into net-next then I can probably do that
 in a follow-up.

-ed

Re: [PATCH] sfc: replace deprecated strncpy with strscpy

[Kees Cook]

On Thu, Oct 12, 2023 at 08:38:19PM +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.
> 
> `desc` is expected to be NUL-terminated as evident by the manual
> NUL-byte assignment. Moreover, NUL-padding does not seem to be
> necessary.
> 
> The only caller of efx_mcdi_nvram_metadata() is
> efx_devlink_info_nvram_partition() which provides a NULL for `desc`:
> |       rc = efx_mcdi_nvram_metadata(efx, partition_type, NULL, version, NULL, 0);
> 
> Due to this, I am not sure this code is even reached but we should still
> favor something other than strncpy.
> 
> 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@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Looks correct to me!

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

-- 
Kees Cook

Re: [PATCH] sfc: replace deprecated strncpy with strscpy

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 12 Oct 2023 20:38:19 +0000 you 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.
> 
> `desc` is expected to be NUL-terminated as evident by the manual
> NUL-byte assignment. Moreover, NUL-padding does not seem to be
> necessary.
> 
> [...]

Here is the summary with links:
  - sfc: replace deprecated strncpy with strscpy
    https://git.kernel.org/netdev/net-next/c/220dd227ca3a

You are awesome, thank you!
-- 
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