net: mlx4: Use scnprintf() for avoiding potential buffer overflow

Since snprintf() returns the would-be-output size instead of the
actual output size, the succeeding calls may go beyond the given
buffer limit.  Fix it by replacing with scnprintf().

Cc: "David S . Miller" <davem@davemloft.net>
Cc: Tariq Toukan <tariqt@mellanox.com>
To: netdev@vger.kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/mcg.c

@@ -906,32 +906,32 @@ static void mlx4_err_rule(struct mlx4_dev *dev, char *str,
 	int len = 0;
 
 	mlx4_err(dev, "%s", str);
-	len += snprintf(buf + len, BUF_SIZE - len,
+	len += scnprintf(buf + len, BUF_SIZE - len,
 			 "port = %d prio = 0x%x qp = 0x%x ",
 			 rule->port, rule->priority, rule->qpn);
 
 	list_for_each_entry(cur, &rule->list, list) {
 		switch (cur->id) {
 		case MLX4_NET_TRANS_RULE_ID_ETH:
-			len += snprintf(buf + len, BUF_SIZE - len,
+			len += scnprintf(buf + len, BUF_SIZE - len,
 					 "dmac = %pM ", &cur->eth.dst_mac);
 			if (cur->eth.ether_type)
-				len += snprintf(buf + len, BUF_SIZE - len,
+				len += scnprintf(buf + len, BUF_SIZE - len,
 						 "ethertype = 0x%x ",
 						 be16_to_cpu(cur->eth.ether_type));
 			if (cur->eth.vlan_id)
-				len += snprintf(buf + len, BUF_SIZE - len,
+				len += scnprintf(buf + len, BUF_SIZE - len,
 						 "vlan-id = %d ",
 						 be16_to_cpu(cur->eth.vlan_id));
 			break;
 
 		case MLX4_NET_TRANS_RULE_ID_IPV4:
 			if (cur->ipv4.src_ip)
-				len += snprintf(buf + len, BUF_SIZE - len,
+				len += scnprintf(buf + len, BUF_SIZE - len,
 						 "src-ip = %pI4 ",
 						 &cur->ipv4.src_ip);
 			if (cur->ipv4.dst_ip)
-				len += snprintf(buf + len, BUF_SIZE - len,
+				len += scnprintf(buf + len, BUF_SIZE - len,
 						 "dst-ip = %pI4 ",
 						 &cur->ipv4.dst_ip);
 			break;
@@ -939,25 +939,25 @@ static void mlx4_err_rule(struct mlx4_dev *dev, char *str,
 		case MLX4_NET_TRANS_RULE_ID_TCP:
 		case MLX4_NET_TRANS_RULE_ID_UDP:
 			if (cur->tcp_udp.src_port)
-				len += snprintf(buf + len, BUF_SIZE - len,
+				len += scnprintf(buf + len, BUF_SIZE - len,
 						 "src-port = %d ",
 						 be16_to_cpu(cur->tcp_udp.src_port));
 			if (cur->tcp_udp.dst_port)
-				len += snprintf(buf + len, BUF_SIZE - len,
+				len += scnprintf(buf + len, BUF_SIZE - len,
 						 "dst-port = %d ",
 						 be16_to_cpu(cur->tcp_udp.dst_port));
 			break;
 
 		case MLX4_NET_TRANS_RULE_ID_IB:
-			len += snprintf(buf + len, BUF_SIZE - len,
+			len += scnprintf(buf + len, BUF_SIZE - len,
 					 "dst-gid = %pI6\n", cur->ib.dst_gid);
-			len += snprintf(buf + len, BUF_SIZE - len,
+			len += scnprintf(buf + len, BUF_SIZE - len,
 					 "dst-gid-mask = %pI6\n",
 					 cur->ib.dst_gid_msk);
 			break;
 
 		case MLX4_NET_TRANS_RULE_ID_VXLAN:
-			len += snprintf(buf + len, BUF_SIZE - len,
+			len += scnprintf(buf + len, BUF_SIZE - len,
 					 "VNID = %d ", be32_to_cpu(cur->vxlan.vni));
 			break;
 		case MLX4_NET_TRANS_RULE_ID_IPV6:
@@ -967,7 +967,7 @@ static void mlx4_err_rule(struct mlx4_dev *dev, char *str,
 			break;
 		}
 	}
-	len += snprintf(buf + len, BUF_SIZE - len, "\n");
+	len += scnprintf(buf + len, BUF_SIZE - len, "\n");
 	mlx4_err(dev, "%s", buf);
 
 	if (len >= BUF_SIZE)