linux-kernel - [PATCH] isdn: replace deprecated strncpy with strscpy

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Message-ID: <20230922-strncpy-drivers-isdn-misdn-clock-c-v1-1-3ba2a5ae627a@google.com>
Date:   Fri, 22 Sep 2023 11:58:06 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Karsten Keil <isdn@...ux-pingi.de>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] isdn: replace deprecated strncpy with strscpy

`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 `iclock->name` to be NUL-terminated based on its use within
printk:
|	printk(KERN_DEBUG "%s: %s %d\n", __func__, iclock->name,
|	       iclock->pri);

`iclock` is zero-initialized and as such is already NUL-padded which
means strncpy is doing extra work here by eagerly NUL-padding the
destination buffer.

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without 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@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Note: build-tested only.
---
 drivers/isdn/mISDN/clock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/isdn/mISDN/clock.c b/drivers/isdn/mISDN/clock.c
index 01d878168ef2..f71eb61db131 100644
--- a/drivers/isdn/mISDN/clock.c
+++ b/drivers/isdn/mISDN/clock.c
@@ -96,7 +96,7 @@ struct mISDNclock
 		printk(KERN_ERR "%s: No memory for clock entry.\n", __func__);
 		return NULL;
 	}
-	strncpy(iclock->name, name, sizeof(iclock->name) - 1);
+	strscpy(iclock->name, name, sizeof(iclock->name));
 	iclock->pri = pri;
 	iclock->priv = priv;
 	iclock->ctl = ctl;

---
base-commit: 2cf0f715623872823a72e451243bbf555d10d032
change-id: 20230922-strncpy-drivers-isdn-misdn-clock-c-2d32a23b8c2d

Best regards,
--
Justin Stitt <justinstitt@...gle.com>