linux-hardening - [PATCH v2] atmel: replace deprecated strncpy with strscpy

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Date: Thu, 19 Oct 2023 17:29:01 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Kalle Valo <kvalo@...nel.org>
Cc: linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH v2] atmel: 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 priv->firmware_id to be NUL-terminated based on its usage
with seq_printf() and strlen() in atmel.c:
1420 |       seq_printf(m, "%s loaded by host\n", priv->firmware_id);
...
3884 |       if (strlen(priv->firmware_id) == 0) {

NUL-padding is not required, which is evident by the usage of a plain
strcpy():
3891 |   strcpy(priv->firmware_id, "atmel_at76c502.bin");

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.

Let's also replace hard-coded lengths to be `sizeof(...)` for buffers
that the compiler can detect the size for as this is less error prone.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy [2]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [3]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Changes in v2:
- leave strcpy() usage as is (thanks Kees)
- Link to v1: https://lore.kernel.org/r/20231016-strncpy-drivers-net-wireless-atmel-atmel-c-v1-1-038d0e73c402@google.com
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/net/wireless/atmel/atmel.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/wireless/atmel/atmel.c b/drivers/net/wireless/atmel/atmel.c
index 7c2d1c588156..99920430e8b4 100644
--- a/drivers/net/wireless/atmel/atmel.c
+++ b/drivers/net/wireless/atmel/atmel.c
@@ -2651,8 +2651,7 @@ static int atmel_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
 
 		priv->firmware = new_firmware;
 		priv->firmware_length = com.len;
-		strncpy(priv->firmware_id, com.id, 31);
-		priv->firmware_id[31] = '\0';
+		strscpy(priv->firmware_id, com.id, sizeof(priv->firmware_id));
 		break;
 
 	case ATMELRD:

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231016-strncpy-drivers-net-wireless-atmel-atmel-c-7ca951cf7cfa

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