linux/dim: Fix overflow in dim calculation

While using net_dim, a dim_sample was used without ever initializing the
comps value. Added use of DIV_ROUND_DOWN_ULL() to prevent potential
overflow, it should not be a problem to save the final result in an int
because after the division by epms the value should not be larger than a
few thousand.

[ 1040.127124] UBSAN: Undefined behaviour in lib/dim/dim.c:78:23
[ 1040.130118] signed integer overflow:
[ 1040.131643] 134718714 * 100 cannot be represented in type 'int'

Fixes: 398c2b05 ("linux/dim: Add completions count to dim_sample")
Signed-off-by: Yamin Friedman <yaminf@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bcmsysport.c

@@ -992,7 +992,7 @@ static int bcm_sysport_poll(struct napi_struct *napi, int budget)
 {
 	struct bcm_sysport_priv *priv =
 		container_of(napi, struct bcm_sysport_priv, napi);
-	struct dim_sample dim_sample;
+	struct dim_sample dim_sample = {};
 	unsigned int work_done = 0;
 
 	work_done = bcm_sysport_desc_rx(priv, budget);

drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -2136,7 +2136,7 @@ static int bnxt_poll(struct napi_struct *napi, int budget)
 		}
 	}
 	if (bp->flags & BNXT_FLAG_DIM) {
-		struct dim_sample dim_sample;
+		struct dim_sample dim_sample = {};
 
 		dim_update_sample(cpr->event_ctr,
 				  cpr->rx_packets,

drivers/net/ethernet/broadcom/genet/bcmgenet.c

@@ -1895,7 +1895,7 @@ static int bcmgenet_rx_poll(struct napi_struct *napi, int budget)
 {
 	struct bcmgenet_rx_ring *ring = container_of(napi,
 			struct bcmgenet_rx_ring, napi);
-	struct dim_sample dim_sample;
+	struct dim_sample dim_sample = {};
 	unsigned int work_done;
 
 	work_done = bcmgenet_desc_rx(ring, budget);

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

@@ -49,7 +49,7 @@ static inline bool mlx5e_channel_no_affinity_change(struct mlx5e_channel *c)
 static void mlx5e_handle_tx_dim(struct mlx5e_txqsq *sq)
 {
 	struct mlx5e_sq_stats *stats = sq->stats;
-	struct dim_sample dim_sample;
+	struct dim_sample dim_sample = {};
 
 	if (unlikely(!test_bit(MLX5E_SQ_STATE_AM, &sq->state)))
 		return;
@@ -61,7 +61,7 @@ static void mlx5e_handle_tx_dim(struct mlx5e_txqsq *sq)
 static void mlx5e_handle_rx_dim(struct mlx5e_rq *rq)
 {
 	struct mlx5e_rq_stats *stats = rq->stats;
-	struct dim_sample dim_sample;
+	struct dim_sample dim_sample = {};
 
 	if (unlikely(!test_bit(MLX5E_RQ_STATE_AM, &rq->state)))
 		return;

lib/dim/dim.c

@@ -74,8 +74,8 @@ void dim_calc_stats(struct dim_sample *start, struct dim_sample *end,
 					delta_us);
 	curr_stats->cpms = DIV_ROUND_UP(ncomps * USEC_PER_MSEC, delta_us);
 	if (curr_stats->epms != 0)
-		curr_stats->cpe_ratio =
-				(curr_stats->cpms * 100) / curr_stats->epms;
+		curr_stats->cpe_ratio = DIV_ROUND_DOWN_ULL(
+			curr_stats->cpms * 100, curr_stats->epms);
 	else
 		curr_stats->cpe_ratio = 0;