`strncpy` is deprecated for use on NUL-terminated destination strings [1].

A suitable replacement is `strscpy` [2] due to the fact that it
guarantees NUL-termination on its destination buffer argument which is
_not_ the case for `strncpy`!

It was pretty difficult, in this case, to try and figure out whether or
not the destination buffer was zero-initialized. If it is and this
behavior is relied on then perhaps `strscpy_pad` is the preferred
option here.

Kees was able to help me out and identify the following code snippet
which seems to show that the destination buffer is zero-initialized.

|       skl = devm_kzalloc(&pci->dev, sizeof(*skl), GFP_KERNEL);

With this information, I opted for `strscpy` since padding is seemingly
not required.

[1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
[2]: manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html

Link: https://github.com/KSPP/linux/issues/90
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- Remove extraneous logic change (thanks Kees)
- Link to v1: https://lore.kernel.org/r/20230726-asoc-intel-skylake-remove-deprecated-strncpy-v1-1-020e04184c7d@google.com
---
 sound/soc/intel/skylake/skl-topology.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/soc/intel/skylake/skl-topology.c b/sound/soc/intel/skylake/skl-topology.c
index 96cfebded072..0ead3ea605cd 100644
--- a/sound/soc/intel/skylake/skl-topology.c
+++ b/sound/soc/intel/skylake/skl-topology.c
@@ -3159,7 +3159,7 @@ static int skl_tplg_fill_str_mfest_tkn(struct device *dev,
 			return -EINVAL;
 		}
 
-		strncpy(skl->lib_info[ref_count].name,
+		strscpy(skl->lib_info[ref_count].name,
 			str_elem->string,
 			ARRAY_SIZE(skl->lib_info[ref_count].name));
 		ref_count++;

---
base-commit: 0b4a9fdc9317440a71d4d4c264a5650bf4a90f3c
change-id: 20230726-asoc-intel-skylake-remove-deprecated-strncpy-9dbcfc26040c

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

On Thu, Jul 27, 2023 at 08:30:18PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on its destination buffer argument which is
> _not_ the case for `strncpy`!
> 
> It was pretty difficult, in this case, to try and figure out whether or
> not the destination buffer was zero-initialized. If it is and this
> behavior is relied on then perhaps `strscpy_pad` is the preferred
> option here.
> 
> Kees was able to help me out and identify the following code snippet
> which seems to show that the destination buffer is zero-initialized.
> 
> |       skl = devm_kzalloc(&pci->dev, sizeof(*skl), GFP_KERNEL);
> 
> With this information, I opted for `strscpy` since padding is seemingly
> not required.
> 
> [1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
> [2]: manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
> 
> Link: https://github.com/KSPP/linux/issues/90
> Suggested-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Thanks for the updates! And based on the details from Amadeusz, it
looks safe.

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

-- 
Kees Cook

On Thu, Jul 27, 2023 at 08:30:18PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on its destination buffer argument which is
> _not_ the case for `strncpy`!

Please don't send new patches in reply to old patches or serieses, this
makes it harder for both people and tools to understand what is going
on - it can bury things in mailboxes and make it difficult to keep track
of what current patches are, both for the new patches and the old ones.

On Fri, Jul 28, 2023 at 12:27:24AM +0100, Mark Brown wrote:
> On Thu, Jul 27, 2023 at 08:30:18PM +0000, Justin Stitt wrote:
> > `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> > 
> > A suitable replacement is `strscpy` [2] due to the fact that it
> > guarantees NUL-termination on its destination buffer argument which is
> > _not_ the case for `strncpy`!
> 
> Please don't send new patches in reply to old patches or serieses, this
> makes it harder for both people and tools to understand what is going
> on - it can bury things in mailboxes and make it difficult to keep track
> of what current patches are, both for the new patches and the old ones.

Hm, I see "X-Mailer: b4 0.12.3". Is this a default behavior of b4? (If
so, that needs fixing.)

-- 
Kees Cook

On Fri, Jul 28, 2023 at 11:56:08AM -0700, Kees Cook wrote:
> On Fri, Jul 28, 2023 at 12:27:24AM +0100, Mark Brown wrote:

> > Please don't send new patches in reply to old patches or serieses, this
> > makes it harder for both people and tools to understand what is going
> > on - it can bury things in mailboxes and make it difficult to keep track
> > of what current patches are, both for the new patches and the old ones.

> Hm, I see "X-Mailer: b4 0.12.3". Is this a default behavior of b4? (If
> so, that needs fixing.)

I've not noticed it doing that for my outbound patches and can't find
any option I tweaked to make it send as new threads, nor can I remember
configuring anything.  There is a b4.send-same-thread option since v0.13
but it's default no according to the documentation:

   https://b4.docs.kernel.org/en/latest/config.html#contributor-oriented-settings