[PATCH] s390/ctcm: replace deprecated strncpy with strscpy

[PATCH] s390/ctcm: 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.

We expect chid to be NUL-terminated based on its use with format
strings:

	CTCM_DBF_TEXT_(SETUP, CTC_DBF_INFO, "%s(%s) %s", CTCM_FUNTAIL,
			chid, ok ? "OK" : "failed");

Moreover, NUL-padding is not required as it is _only_ used in this one
instance with a format string.

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.

We can also drop the +1 from chid's declaration as we no longer need to
be cautious about leaving a spot for a NUL-byte. Let's use the more
idiomatic strscpy usage of (dest, src, sizeof(dest)) as this more
closely ties the destination buffer to the length.

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/s390/net/ctcm_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/net/ctcm_main.c b/drivers/s390/net/ctcm_main.c
index 6faf27136024..ac15d7c2b200 100644
--- a/drivers/s390/net/ctcm_main.c
+++ b/drivers/s390/net/ctcm_main.c
@@ -200,13 +200,13 @@ static void channel_free(struct channel *ch)
 static void channel_remove(struct channel *ch)
 {
 	struct channel **c = &channels;
-	char chid[CTCM_ID_SIZE+1];
+	char chid[CTCM_ID_SIZE];
 	int ok = 0;
 
 	if (ch == NULL)
 		return;
 	else
-		strncpy(chid, ch->id, CTCM_ID_SIZE);
+		strscpy(chid, ch->id, sizeof(chid));
 
 	channel_free(ch);
 	while (*c) {

---
base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
change-id: 20231023-strncpy-drivers-s390-net-ctcm_main-c-f9180f470c69

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

Re: [PATCH] s390/ctcm: replace deprecated strncpy with strscpy

[Thorsten Winkler]

On 23.10.23 21:35, 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 chid to be NUL-terminated based on its use with format
> strings:
> 
> 	CTCM_DBF_TEXT_(SETUP, CTC_DBF_INFO, "%s(%s) %s", CTCM_FUNTAIL,
> 			chid, ok ? "OK" : "failed");
> 
> Moreover, NUL-padding is not required as it is _only_ used in this one
> instance with a format string.
> 
> 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.
> 
> We can also drop the +1 from chid's declaration as we no longer need to
> be cautious about leaving a spot for a NUL-byte. Let's use the more
> idiomatic strscpy usage of (dest, src, sizeof(dest)) as this more
> closely ties the destination buffer to the length.
> 
> 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>

LGTM, thank you!

Reviewed-by: Thorsten Winkler <twinkler@linux.ibm.com>
Tested-by: Thorsten Winkler <twinkler@linux.ibm.com>

> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>   drivers/s390/net/ctcm_main.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/s390/net/ctcm_main.c b/drivers/s390/net/ctcm_main.c
> index 6faf27136024..ac15d7c2b200 100644
> --- a/drivers/s390/net/ctcm_main.c
> +++ b/drivers/s390/net/ctcm_main.c
> @@ -200,13 +200,13 @@ static void channel_free(struct channel *ch)
>   static void channel_remove(struct channel *ch)
>   {
>   	struct channel **c = &channels;
> -	char chid[CTCM_ID_SIZE+1];
> +	char chid[CTCM_ID_SIZE];
>   	int ok = 0;
>   
>   	if (ch == NULL)
>   		return;
>   	else
> -		strncpy(chid, ch->id, CTCM_ID_SIZE);
> +		strscpy(chid, ch->id, sizeof(chid));
>   
>   	channel_free(ch);
>   	while (*c) {
> 
> ---
> base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
> change-id: 20231023-strncpy-drivers-s390-net-ctcm_main-c-f9180f470c69
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 
> 

Re: [PATCH] s390/ctcm: replace deprecated strncpy with strscpy

[Kees Cook]

On Mon, Oct 23, 2023 at 07:35:07PM +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 chid to be NUL-terminated based on its use with format
> strings:
> 
> 	CTCM_DBF_TEXT_(SETUP, CTC_DBF_INFO, "%s(%s) %s", CTCM_FUNTAIL,
> 			chid, ok ? "OK" : "failed");
> 
> Moreover, NUL-padding is not required as it is _only_ used in this one
> instance with a format string.
> 
> 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.
> 
> We can also drop the +1 from chid's declaration as we no longer need to
> be cautious about leaving a spot for a NUL-byte. Let's use the more
> idiomatic strscpy usage of (dest, src, sizeof(dest)) as this more
> closely ties the destination buffer to the length.
> 
> 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>

Yeah, all looks correct to me.

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

-- 
Kees Cook

Re: [PATCH] s390/ctcm: 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 Mon, 23 Oct 2023 19:35:07 +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.
> 
> We expect chid to be NUL-terminated based on its use with format
> strings:
> 
> [...]

Here is the summary with links:
  - s390/ctcm: replace deprecated strncpy with strscpy
    https://git.kernel.org/netdev/net-next/c/19d1c64b7741

You are awesome, thank you!
-- 
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