net/mlx5e: Fix wraparound in rate limiting for values above 255 Gbps

Add validation to reject rates exceeding 255 Gbps that would overflow
the 8 bits max bandwidth field.

Fixes: d888079 ("net/mlx5e: Implement DCBNL IEEE max rate")
Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/1762681073-1084058-5-git-send-email-tariqt@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: gal-pressman

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

@@ -596,11 +596,13 @@ static int mlx5e_dcbnl_ieee_setmaxrate(struct net_device *netdev,
 	u8 max_bw_value[IEEE_8021QAZ_MAX_TCS];
 	u8 max_bw_unit[IEEE_8021QAZ_MAX_TCS];
 	__u64 upper_limit_mbps;
+	__u64 upper_limit_gbps;
 	int i;
 
 	memset(max_bw_value, 0, sizeof(max_bw_value));
 	memset(max_bw_unit, 0, sizeof(max_bw_unit));
 	upper_limit_mbps = 255 * MLX5E_100MB;
+	upper_limit_gbps = 255 * MLX5E_1GB;
 
 	for (i = 0; i <= mlx5_max_tc(mdev); i++) {
 		if (!maxrate->tc_maxrate[i]) {
@@ -612,10 +614,16 @@ static int mlx5e_dcbnl_ieee_setmaxrate(struct net_device *netdev,
 						  MLX5E_100MB);
 			max_bw_value[i] = max_bw_value[i] ? max_bw_value[i] : 1;
 			max_bw_unit[i]  = MLX5_100_MBPS_UNIT;
-		} else {
+		} else if (max_bw_value[i] <= upper_limit_gbps) {
 			max_bw_value[i] = div_u64(maxrate->tc_maxrate[i],
 						  MLX5E_1GB);
 			max_bw_unit[i]  = MLX5_GBPS_UNIT;
+		} else {
+			netdev_err(netdev,
+				   "tc_%d maxrate %llu Kbps exceeds limit %llu\n",
+				   i, maxrate->tc_maxrate[i],
+				   upper_limit_gbps);
+			return -EINVAL;
 		}
 	}