Re: [PATCH] video: fbdev: fsl-diu-fb: replace deprecated strncpy with strscpy_pad

[Kees Cook]

On Wed, Mar 20, 2024 at 10:48:50PM +, 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.
> 
> A better alternative is strscpy() as it guarantees NUL-termination on
> the destination buffer.
> 
> Since we are eventually copying over to userspace, let's ensure we
> NUL-pad the destination buffer by using the pad variant of strscpy.
> - core/fb_chrdev.c:
> 234 | err = copy_to_user(>id, >id, sizeof(fix32->id));
> 
> Furthermore, we can use the new 2-argument variants of strscpy() and
> strscpy_pad() introduced by Commit e6584c3964f2f ("string: Allow
> 2-argument strscpy()") to simplify the syntax even more.
> 
> 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-harden...@vger.kernel.org
> Signed-off-by: Justin Stitt 

Reviewed-by: Kees Cook 

-- 
Kees Cook

[PATCH] video: fbdev: fsl-diu-fb: replace deprecated strncpy with strscpy_pad

[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.

A better alternative is strscpy() as it guarantees NUL-termination on
the destination buffer.

Since we are eventually copying over to userspace, let's ensure we
NUL-pad the destination buffer by using the pad variant of strscpy.
- core/fb_chrdev.c:
234 |   err = copy_to_user(>id, >id, sizeof(fix32->id));

Furthermore, we can use the new 2-argument variants of strscpy() and
strscpy_pad() introduced by Commit e6584c3964f2f ("string: Allow
2-argument strscpy()") to simplify the syntax even more.

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-harden...@vger.kernel.org
Signed-off-by: Justin Stitt 
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/video/fbdev/fsl-diu-fb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/fsl-diu-fb.c b/drivers/video/fbdev/fsl-diu-fb.c
index 0191141657fd..ea37a60da10c 100644
--- a/drivers/video/fbdev/fsl-diu-fb.c
+++ b/drivers/video/fbdev/fsl-diu-fb.c
@@ -787,7 +787,7 @@ static void set_fix(struct fb_info *info)
struct fb_var_screeninfo *var = >var;
struct mfb_info *mfbi = info->par;
 
-   strncpy(fix->id, mfbi->id, sizeof(fix->id));
+   strscpy_pad(fix->id, mfbi->id);
fix->line_length = var->xres_virtual * var->bits_per_pixel / 8;
fix->type = FB_TYPE_PACKED_PIXELS;
fix->accel = FB_ACCEL_NONE;

---
base-commit: bf3a69c6861ff4dc7892d895c87074af7bc1c400
change-id: 20240319-strncpy-drivers-video-fbdev-fsl-diu-fb-c-b69036ceb3f4

Best regards,
--
Justin Stitt