[PATCH v2] net: dsa: vsc73xx: replace deprecated strncpy with ethtool_sprintf

[Justin Stitt <justinstitt@google.com>]

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

ethtool_sprintf() is designed specifically for get_strings() usage.
Let's replace strncpy in favor of this more robust and easier to
understand interface.

This change could result in misaligned strings when if(cnt) fails. To
combat this, use ternary to place empty string in buffer and properly
increment pointer to next string slot.

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@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- Prevent misaligned string assignments (thanks Vladimir)
- Link to v1: https://lore.kernel.org/r/20231009-strncpy-drivers-net-dsa-vitesse-vsc73xx-core-c-v1-1-e2427e087fad@google.com
---
Note: build-tested only.
---
 drivers/net/dsa/vitesse-vsc73xx-core.c | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/drivers/net/dsa/vitesse-vsc73xx-core.c b/drivers/net/dsa/vitesse-vsc73xx-core.c
index 4f09e7438f3b..56dc3e7884fd 100644
--- a/drivers/net/dsa/vitesse-vsc73xx-core.c
+++ b/drivers/net/dsa/vitesse-vsc73xx-core.c
@@ -928,7 +928,8 @@ static void vsc73xx_get_strings(struct dsa_switch *ds, int port, u32 stringset,
 	const struct vsc73xx_counter *cnt;
 	struct vsc73xx *vsc = ds->priv;
 	u8 indices[6];
-	int i, j;
+	u8 *buf = data;
+	int i;
 	u32 val;
 	int ret;
 
@@ -948,10 +949,7 @@ static void vsc73xx_get_strings(struct dsa_switch *ds, int port, u32 stringset,
 	indices[5] = ((val >> 26) & 0x1f); /* TX counter 2 */
 
 	/* The first counters is the RX octets */
-	j = 0;
-	strncpy(data + j * ETH_GSTRING_LEN,
-		"RxEtherStatsOctets", ETH_GSTRING_LEN);
-	j++;
+	ethtool_sprintf(&buf, "RxEtherStatsOctets");
 
 	/* Each port supports recording 3 RX counters and 3 TX counters,
 	 * figure out what counters we use in this set-up and return the
@@ -961,23 +959,16 @@ static void vsc73xx_get_strings(struct dsa_switch *ds, int port, u32 stringset,
 	 */
 	for (i = 0; i < 3; i++) {
 		cnt = vsc73xx_find_counter(vsc, indices[i], false);
-		if (cnt)
-			strncpy(data + j * ETH_GSTRING_LEN,
-				cnt->name, ETH_GSTRING_LEN);
-		j++;
+		ethtool_sprintf(&buf, "%s", cnt ? cnt->name : "");
 	}
 
 	/* TX stats begins with the number of TX octets */
-	strncpy(data + j * ETH_GSTRING_LEN,
-		"TxEtherStatsOctets", ETH_GSTRING_LEN);
-	j++;
+	ethtool_sprintf(&buf, "TxEtherStatsOctets");
 
 	for (i = 3; i < 6; i++) {
 		cnt = vsc73xx_find_counter(vsc, indices[i], true);
-		if (cnt)
-			strncpy(data + j * ETH_GSTRING_LEN,
-				cnt->name, ETH_GSTRING_LEN);
-		j++;
+		ethtool_sprintf(&buf, "%s", cnt ? cnt->name : "");
+
 	}
 }
 

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231009-strncpy-drivers-net-dsa-vitesse-vsc73xx-core-c-1cfd0ac2d81b

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