2024-03-20 23:04:58

by Justin Stitt

Subject: [PATCH] fbdev: uvesafb: 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.

We expect v86d_path to be NUL-terminated based on its use with the
C-string format specifier in printf-likes:
| pr_err("failed to execute %s\n", v86d_path);
and
| return snprintf(buf, PAGE_SIZE, "%s\n", v86d_path);

Let's also opt to pad v86d_path since it may get used in and around
userspace:
| return call_usermodehelper(v86d_path, argv, envp, UMH_WAIT_PROC);

Considering the above, strscpy_pad() is the best replacement as it
guarantees both NUL-termination and NUL-padding on the destination
buffer.

Note that this patch relies on the _new_ 2-argument versions of
strscpy() and strscpy_pad() introduced in Commit e6584c3964f2f ("string:
Allow 2-argument strscpy()").

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
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/uvesafb.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/uvesafb.c b/drivers/video/fbdev/uvesafb.c
index e1f421e91b4f..8b554fcf1bfb 100644
--- a/drivers/video/fbdev/uvesafb.c
+++ b/drivers/video/fbdev/uvesafb.c
@@ -1867,7 +1867,7 @@ static ssize_t v86d_show(struct device_driver *dev, char *buf)
static ssize_t v86d_store(struct device_driver *dev, const char *buf,
size_t count)
{
- strncpy(v86d_path, buf, PATH_MAX - 1);
+ strscpy_pad(v86d_path, buf);
return count;
}
static DRIVER_ATTR_RW(v86d);

---
base-commit: a4145ce1e7bc247fd6f2846e8699473448717b37
change-id: 20240320-strncpy-drivers-video-fbdev-uvesafb-c-43668c4ef6c8

Best regards,
--
Justin Stitt <[email protected]>

2024-03-29 04:05:40

by Kees Cook

Subject: Re: [PATCH] fbdev: uvesafb: replace deprecated strncpy with strscpy_pad

On Wed, Mar 20, 2024 at 11:04:44PM +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 expect v86d_path to be NUL-terminated based on its use with the
> C-string format specifier in printf-likes:
> | pr_err("failed to execute %s\n", v86d_path);
> and
> | return snprintf(buf, PAGE_SIZE, "%s\n", v86d_path);
>
> Let's also opt to pad v86d_path since it may get used in and around
> userspace:
> | return call_usermodehelper(v86d_path, argv, envp, UMH_WAIT_PROC);
>
> Considering the above, strscpy_pad() is the best replacement as it
> guarantees both NUL-termination and NUL-padding on the destination
> buffer.
>
> Note that this patch relies on the _new_ 2-argument versions of
> strscpy() and strscpy_pad() introduced in Commit e6584c3964f2f ("string:
> Allow 2-argument strscpy()").
>
> 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
> 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