net: qualcomm: rmnet: Fix possible null dereference in command processing

If a command packet with invalid mux id is received, the packet would
not have a valid endpoint. This invalid endpoint maybe dereferenced
leading to a crash. Identified by manual code inspection.

Fixes: 3352e6c4 ("net: qualcomm: rmnet: Convert the muxed endpoint to hlist")
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c

@@ -38,6 +38,11 @@ static u8 rmnet_map_do_flow_control(struct sk_buff *skb,
 	}
 
 	ep = rmnet_get_endpoint(port, mux_id);
+	if (!ep) {
+		kfree_skb(skb);
+		return RX_HANDLER_CONSUMED;
+	}
+
 	vnd = ep->egress_dev;
 
 	ip_family = cmd->flow_control.ip_family;