net/mlx4_core: Fix access to uninitialized index

BugLink: https://bugs.launchpad.net/bugs/1878232

commit 2bb07e15 upstream.

Prevent using uninitialized or negative index when handling
steering entries.

Fixes: b12d93d6 ('mlx4: Add support for promiscuous mode in the new steering model.')
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

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

@@ -1109,7 +1109,7 @@ int mlx4_qp_attach_common(struct mlx4_dev *dev, struct mlx4_qp *qp, u8 gid[16],
 	struct mlx4_cmd_mailbox *mailbox;
 	struct mlx4_mgm *mgm;
 	u32 members_count;
-	int index, prev;
+	int index = -1, prev;
 	int link = 0;
 	int i;
 	int err;
@@ -1188,7 +1188,7 @@ int mlx4_qp_attach_common(struct mlx4_dev *dev, struct mlx4_qp *qp, u8 gid[16],
 		goto out;
 
 out:
-	if (prot == MLX4_PROT_ETH) {
+	if (prot == MLX4_PROT_ETH && index != -1) {
 		/* manage the steering entry for promisc mode */
 		if (new_entry)
 			err = new_steering_entry(dev, port, steer,