net/mlx5e: Check return value of snprintf writing to fw_version buffer for representors

Treat the operation as an error case when the return value is equivalent to
the size of the name buffer. Failed to write null terminator to the name
buffer, making the string malformed and should not be used. Provide a
string with only the firmware version when forming the string with the
board id fails. This logic for representors is identical to normal flow
with ethtool.

Without check, will trigger -Wformat-truncation with W=1.

    drivers/net/ethernet/mellanox/mlx5/core/en_rep.c: In function 'mlx5e_rep_get_drvinfo':
    drivers/net/ethernet/mellanox/mlx5/core/en_rep.c:78:31: warning: '%.16s' directive output may be truncated writing up to 16 bytes into a region of size between 13 and 22 [-Wformat-truncation=]
      78 |                  "%d.%d.%04d (%.16s)",
         |                               ^~~~~
    drivers/net/ethernet/mellanox/mlx5/core/en_rep.c:77:9: note: 'snprintf' output between 12 and 37 bytes into a destination of size 32
      77 |         snprintf(drvinfo->fw_version, sizeof(drvinfo->fw_version),
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      78 |                  "%d.%d.%04d (%.16s)",
         |                  ~~~~~~~~~~~~~~~~~~~~~
      79 |                  fw_rev_maj(mdev), fw_rev_min(mdev),
         |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      80 |                  fw_rev_sub(mdev), mdev->board_id);
         |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: cf83c8fd ("net/mlx5e: Add missing ethtool driver info for representors")
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6d4ab2e97dcfbcd748ae71761a9d8e5e41cc732cSigned-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Link: https://lore.kernel.org/r/20231114215846.5902-16-saeed@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlx5/core/en_rep.c

@@ -71,13 +71,17 @@ static void mlx5e_rep_get_drvinfo(struct net_device *dev,
 {
 	struct mlx5e_priv *priv = netdev_priv(dev);
 	struct mlx5_core_dev *mdev = priv->mdev;
+	int count;
 
 	strscpy(drvinfo->driver, mlx5e_rep_driver_name,
 		sizeof(drvinfo->driver));
+	count = snprintf(drvinfo->fw_version, sizeof(drvinfo->fw_version),
+			 "%d.%d.%04d (%.16s)", fw_rev_maj(mdev),
+			 fw_rev_min(mdev), fw_rev_sub(mdev), mdev->board_id);
+	if (count == sizeof(drvinfo->fw_version))
 		snprintf(drvinfo->fw_version, sizeof(drvinfo->fw_version),
-		 "%d.%d.%04d (%.16s)",
-		 fw_rev_maj(mdev), fw_rev_min(mdev),
-		 fw_rev_sub(mdev), mdev->board_id);
+			 "%d.%d.%04d", fw_rev_maj(mdev),
+			 fw_rev_min(mdev), fw_rev_sub(mdev));
 }
 
 static const struct counter_desc sw_rep_stats_desc[] = {