2024-03-20 22:49:03

by Justin Stitt

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

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(&fix32->id, &fix->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: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
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 = &info->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 <[email protected]>

2024-03-29 04:06:37

by Kees Cook

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

On Wed, Mar 20, 2024 at 10:48:50PM +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.
>
> 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(&fix32->id, &fix->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: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>

Reviewed-by: Kees Cook <[email protected]>

--
Kees Cook