[PATCH] drm/modes: refactor deprecated strncpy

[Justin Stitt]

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

We should prefer more robust and less ambiguous string interfaces.

A suitable replacement is `strscpy` [2] due to the fact that it guarantees
NUL-termination on the destination buffer and doesn't incur the
performance loss of 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@xxxxxxxxxxxxxxx
Cc: Xu Panda <xu.panda@xxxxxxxxxx>
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
---
This patch is basically a resend of [1] by Xu but rebased onto mainline.

This patch is also similar to:
commit 0f9aa074c92dd ("drm/modes: Use strscpy() to copy command-line mode name")

[1]: https://lore.kernel.org/all/202212051935289159302@xxxxxxxxxx/
---
 drivers/gpu/drm/drm_modes.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..c702a8b866cf 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -2617,8 +2617,7 @@ void drm_mode_convert_to_umode(struct drm_mode_modeinfo *out,
 		break;
 	}
 
-	strncpy(out->name, in->name, DRM_DISPLAY_MODE_LEN);
-	out->name[DRM_DISPLAY_MODE_LEN-1] = 0;
+	strscpy(out->name, in->name, DRM_DISPLAY_MODE_LEN);
 }
 
 /**
@@ -2659,8 +2658,7 @@ int drm_mode_convert_umode(struct drm_device *dev,
 	 * useful for the kernel->userspace direction anyway.
 	 */
 	out->type = in->type & DRM_MODE_TYPE_ALL;
-	strncpy(out->name, in->name, DRM_DISPLAY_MODE_LEN);
-	out->name[DRM_DISPLAY_MODE_LEN-1] = 0;
+	strscpy(out->name, in->name, DRM_DISPLAY_MODE_LEN);
 
 	/* Clearing picture aspect ratio bits from out flags,
 	 * as the aspect-ratio information is not stored in

---
base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
change-id: 20230914-strncpy-drivers-gpu-drm-drm_modes-c-a35d782cad01

Best regards,
--
Justin Stitt <justinstitt@xxxxxxxxxx>