linux-hardening - [PATCH] i40e: use scnprintf over strncpy+strncat

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Message-ID: <20231010-strncpy-drivers-net-ethernet-intel-i40e-i40e_ddp-c-v1-1-f01a23394eab@google.com>
Date: Tue, 10 Oct 2023 20:53:00 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Jesse Brandeburg <jesse.brandeburg@...el.com>, Tony Nguyen <anthony.l.nguyen@...el.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, 
	Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] i40e: use scnprintf over strncpy+strncat

`strncpy` is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

Moreover, `strncat` shouldn't really be used either as per
fortify-string.h:
 * Do not use this function. While FORTIFY_SOURCE tries to avoid
 * read and write overflows, this is only possible when the sizes
 * of @p and @q are known to the compiler. Prefer building the
 * string with formatting, via scnprintf() or similar.

Instead, use `scnprintf` with "%s%s" format string. This code is now
more readable and robust.

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/net/ethernet/intel/i40e/i40e_ddp.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_ddp.c b/drivers/net/ethernet/intel/i40e/i40e_ddp.c
index 0e72abd178ae..ec25e4be250f 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_ddp.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_ddp.c
@@ -438,10 +438,9 @@ int i40e_ddp_flash(struct net_device *netdev, struct ethtool_flash *flash)
 		char profile_name[sizeof(I40E_DDP_PROFILE_PATH)
 				  + I40E_DDP_PROFILE_NAME_MAX];
 
-		profile_name[sizeof(profile_name) - 1] = 0;
-		strncpy(profile_name, I40E_DDP_PROFILE_PATH,
-			sizeof(profile_name) - 1);
-		strncat(profile_name, flash->data, I40E_DDP_PROFILE_NAME_MAX);
+		scnprintf(profile_name, sizeof(profile_name), "%s%s",
+			  I40E_DDP_PROFILE_PATH, flash->data);
+
 		/* Load DDP recipe. */
 		status = request_firmware(&ddp_config, profile_name,
 					  &netdev->dev);

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231010-strncpy-drivers-net-ethernet-intel-i40e-i40e_ddp-c-dd7f20b7ed5d

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