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 know dev->name should be NUL-terminated based on the presence of a
manual NUL-byte assignment.

NUL-padding is not required as dev is already zero-allocated which
renders any further NUL-byte assignments redundant:
dev = pnp_alloc_dev(&pnpacpi_protocol, num, pnpid); --->
  dev = kzalloc(sizeof(struct pnp_dev), GFP_KERNEL);

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. This simplifies the code and makes
the intent/behavior more obvious.

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/pnp/pnpacpi/core.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/pnp/pnpacpi/core.c b/drivers/pnp/pnpacpi/core.c
index 6ab272c84b7b..a0927081a003 100644
--- a/drivers/pnp/pnpacpi/core.c
+++ b/drivers/pnp/pnpacpi/core.c
@@ -250,12 +250,9 @@ static int __init pnpacpi_add_device(struct acpi_device *device)
 		dev->capabilities |= PNP_DISABLE;
 
 	if (strlen(acpi_device_name(device)))
-		strncpy(dev->name, acpi_device_name(device), sizeof(dev->name));
+		strscpy(dev->name, acpi_device_name(device), sizeof(dev->name));
 	else
-		strncpy(dev->name, acpi_device_bid(device), sizeof(dev->name));
-
-	/* Handle possible string truncation */
-	dev->name[sizeof(dev->name) - 1] = '\0';
+		strscpy(dev->name, acpi_device_bid(device), sizeof(dev->name));
 
 	if (dev->active)
 		pnpacpi_parse_allocated_resource(dev);

---
base-commit: dab3e01664eaddae965699f1fec776609db0ea9d
change-id: 20231019-strncpy-drivers-pnp-pnpacpi-core-c-54d9bc42443e

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

On Thu, Oct 19, 2023 at 10:47:58PM +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 know dev->name should be NUL-terminated based on the presence of a
> manual NUL-byte assignment.
> 
> NUL-padding is not required as dev is already zero-allocated which
> renders any further NUL-byte assignments redundant:
> dev = pnp_alloc_dev(&pnpacpi_protocol, num, pnpid); --->
>   dev = kzalloc(sizeof(struct pnp_dev), GFP_KERNEL);
> 
> 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. This simplifies the code and makes
> the intent/behavior more obvious.
> 
> 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 clean to me!

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

-- 
Kees Cook

On Fri, Oct 20, 2023 at 1:06 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Oct 19, 2023 at 10:47:58PM +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 know dev->name should be NUL-terminated based on the presence of a
> > manual NUL-byte assignment.
> >
> > NUL-padding is not required as dev is already zero-allocated which
> > renders any further NUL-byte assignments redundant:
> > dev = pnp_alloc_dev(&pnpacpi_protocol, num, pnpid); --->
> >   dev = kzalloc(sizeof(struct pnp_dev), GFP_KERNEL);
> >
> > 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. This simplifies the code and makes
> > the intent/behavior more obvious.
> >
> > 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 clean to me!
>
> Reviewed-by: Kees Cook <keescook@chromium.org>

Applied as 6.7 material, thanks!