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Date: Wed, 20 Mar 2024 23:04:44 +0000
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Message-ID: <20240320-strncpy-drivers-video-fbdev-uvesafb-c-v1-1-fd6af3766c80@google.com>
Subject: [PATCH] fbdev: uvesafb: replace deprecated strncpy with strscpy_pad
From: Justin Stitt <justinstitt@google.com>
To: Michal Januszewski <spock@gentoo.org>, Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, 
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, 
	Justin Stitt <justinstitt@google.com>
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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: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
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 <justinstitt@google.com>