linux-hardening - [PATCH v2] net: dsa: lan9303: use ethtool_sprintf() for lan9303_get

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Message-ID: <20231005-strncpy-drivers-net-dsa-lan9303-core-c-v2-1-feb452a532db@google.com>
Date: Thu, 05 Oct 2023 18:56:50 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Andrew Lunn <andrew@...n.ch>, Florian Fainelli <f.fainelli@...il.com>, 
	Vladimir Oltean <olteanv@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>, 
	Justin Stitt <justinstitt@...gle.com>, Alexander Lobakin <aleksander.lobakin@...el.com>
Subject: [PATCH v2] net: dsa: lan9303: use ethtool_sprintf() for lan9303_get_strings()

This pattern of strncpy with some pointer arithmetic setting fixed-sized
intervals with string literal data is a bit weird so let's use
ethtool_sprintf() as this has more obvious behavior and is less-error
prone.

Nicely, we also get to drop a usage of the now deprecated strncpy() [1].

One might consider this pattern:
|       ethtool_sprintf(&buf, lan9303_mib[u].name);
... but this triggers a -Wformat-security warning.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
Suggested-by: Alexander Lobakin <aleksander.lobakin@...el.com>
---
Changes in v2:
- use ethtool_sprintf (thanks Alexander)
- Link to v1: https://lore.kernel.org/r/20231005-strncpy-drivers-net-dsa-lan9303-core-c-v1-1-5a66c538147e@google.com
---
Note: build-tested only.
---
 drivers/net/dsa/lan9303-core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/lan9303-core.c b/drivers/net/dsa/lan9303-core.c
index ee67adeb2cdb..95a8e5168c2a 100644
--- a/drivers/net/dsa/lan9303-core.c
+++ b/drivers/net/dsa/lan9303-core.c
@@ -1007,14 +1007,14 @@ static const struct lan9303_mib_desc lan9303_mib[] = {
 static void lan9303_get_strings(struct dsa_switch *ds, int port,
 				u32 stringset, uint8_t *data)
 {
+	u8 *buf = data;
 	unsigned int u;
 
 	if (stringset != ETH_SS_STATS)
 		return;
 
 	for (u = 0; u < ARRAY_SIZE(lan9303_mib); u++) {
-		strncpy(data + u * ETH_GSTRING_LEN, lan9303_mib[u].name,
-			ETH_GSTRING_LEN);
+		ethtool_sprintf(&buf, "%s", lan9303_mib[u].name);
 	}
 }
 

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231005-strncpy-drivers-net-dsa-lan9303-core-c-6386858e5c22

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