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

[PATCH] s390/qeth: 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 new_entry->dbf_name to be NUL-terminated based on its use with
strcmp():
|       if (strcmp(entry->dbf_name, name) == 0) {

Moreover, NUL-padding is not required as new_entry is kzalloc'd just
before this assignment:
|       new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);

... rendering any future NUL-byte assignments (like the ones strncpy()
does) redundant.

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/s390/net/qeth_core_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index cd783290bde5..6af2511e070c 100644
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -6226,7 +6226,7 @@ static int qeth_add_dbf_entry(struct qeth_card *card, char *name)
 	new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);
 	if (!new_entry)
 		goto err_dbg;
-	strncpy(new_entry->dbf_name, name, DBF_NAME_LEN);
+	strscpy(new_entry->dbf_name, name, sizeof(new_entry->dbf_name));
 	new_entry->dbf_info = card->debug;
 	mutex_lock(&qeth_dbf_list_mutex);
 	list_add(&new_entry->dbf_list, &qeth_dbf_list);

---
base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
change-id: 20231023-strncpy-drivers-s390-net-qeth_core_main-c-0b0ee08672ec

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

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

[Thorsten Winkler]

On 23.10.23 21:39, 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 new_entry->dbf_name to be NUL-terminated based on its use with
> strcmp():
> |       if (strcmp(entry->dbf_name, name) == 0) {
> 
> Moreover, NUL-padding is not required as new_entry is kzalloc'd just
> before this assignment:
> |       new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);
> 
> ... rendering any future NUL-byte assignments (like the ones strncpy()
> does) redundant.
> 
> 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>

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/qeth_core_main.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
> index cd783290bde5..6af2511e070c 100644
> --- a/drivers/s390/net/qeth_core_main.c
> +++ b/drivers/s390/net/qeth_core_main.c
> @@ -6226,7 +6226,7 @@ static int qeth_add_dbf_entry(struct qeth_card *card, char *name)
>   	new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);
>   	if (!new_entry)
>   		goto err_dbg;
> -	strncpy(new_entry->dbf_name, name, DBF_NAME_LEN);
> +	strscpy(new_entry->dbf_name, name, sizeof(new_entry->dbf_name));
>   	new_entry->dbf_info = card->debug;
>   	mutex_lock(&qeth_dbf_list_mutex);
>   	list_add(&new_entry->dbf_list, &qeth_dbf_list);
> 
> ---
> base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
> change-id: 20231023-strncpy-drivers-s390-net-qeth_core_main-c-0b0ee08672ec
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 
> 

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

[Kees Cook]

On Mon, Oct 23, 2023 at 07:39:39PM +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 new_entry->dbf_name to be NUL-terminated based on its use with
> strcmp():
> |       if (strcmp(entry->dbf_name, name) == 0) {
> 
> Moreover, NUL-padding is not required as new_entry is kzalloc'd just
> before this assignment:
> |       new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);
> 
> ... rendering any future NUL-byte assignments (like the ones strncpy()
> does) redundant.
> 
> 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>

struct qeth_dbf_entry {
        char dbf_name[DBF_NAME_LEN];

The sizeof() replace looks right to me.

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

-Kees

> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/s390/net/qeth_core_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
> index cd783290bde5..6af2511e070c 100644
> --- a/drivers/s390/net/qeth_core_main.c
> +++ b/drivers/s390/net/qeth_core_main.c
> @@ -6226,7 +6226,7 @@ static int qeth_add_dbf_entry(struct qeth_card *card, char *name)
>  	new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);
>  	if (!new_entry)
>  		goto err_dbg;
> -	strncpy(new_entry->dbf_name, name, DBF_NAME_LEN);
> +	strscpy(new_entry->dbf_name, name, sizeof(new_entry->dbf_name));
>  	new_entry->dbf_info = card->debug;
>  	mutex_lock(&qeth_dbf_list_mutex);
>  	list_add(&new_entry->dbf_list, &qeth_dbf_list);
> 
> ---
> base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
> change-id: 20231023-strncpy-drivers-s390-net-qeth_core_main-c-0b0ee08672ec
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 
> 

-- 
Kees Cook

Re: [PATCH] s390/qeth: 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 19:39:39 +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 new_entry->dbf_name to be NUL-terminated based on its use with
> strcmp():
> |       if (strcmp(entry->dbf_name, name) == 0) {
> 
> [...]

Here is the summary with links:
  - s390/qeth: replace deprecated strncpy with strscpy
    https://git.kernel.org/netdev/net-next/c/e43e6d9582e0

You are awesome, thank you!
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