aws: Force users to use valid network masks on ACL ingress/egress

AWS will accept any overly-specific IP/mask combination, such as
10.1.2.2/24, but will store it by its implied network: 10.1.2.0/24.
This results in hashing errors, because the remote API will return
hashing results out of sync with the local configuration file.

Enforce a stricter API rule than AWS. Force users to use valid masks,
and run a quick calculation on their input to discover their intent.

builtin/providers/aws/network_acl_entry.go

@@ -2,6 +2,7 @@ package aws
 
 import (
 	"fmt"
+	"net"
 	"strconv"
 
 	"github.com/awslabs/aws-sdk-go/aws"
@@ -82,3 +83,17 @@ func validatePorts(to int64, from int64, expected expectedPortPair) bool {
 
 	return true
 }
+
+// validateCIDRBlock ensures the passed CIDR block represents an implied
+// network, and not an overly-specified IP address.
+func validateCIDRBlock(cidr string) error {
+	_, ipnet, err := net.ParseCIDR(cidr)
+	if err != nil {
+		return err
+	}
+	if ipnet.String() != cidr {
+		return fmt.Errorf("%s is not a valid mask; did you mean %s?", cidr, ipnet)
+	}
+
+	return nil
+}

builtin/providers/aws/network_acl_entry_test.go

@@ -152,3 +152,23 @@ func Test_validatePorts(t *testing.T) {
 		}
 	}
 }
+
+func Test_validateCIDRBlock(t *testing.T) {
+	for _, ts := range []struct {
+		cidr      string
+		shouldErr bool
+	}{
+		{"10.2.2.0/24", false},
+		{"10.2.2.0/1234", true},
+		{"10/24", true},
+		{"10.2.2.2/24", true},
+	} {
+		err := validateCIDRBlock(ts.cidr)
+		if ts.shouldErr && err == nil {
+			t.Fatalf("Input '%s' should error but didn't!", ts.cidr)
+		}
+		if !ts.shouldErr && err != nil {
+			t.Fatalf("Got unexpected error for '%s' input: %s", ts.cidr, err)
+		}
+	}
+}

builtin/providers/aws/resource_aws_network_acl.go

@@ -284,8 +284,16 @@ func updateNetworkAclEntries(d *schema.ResourceData, entryType string, conn *ec2
 			}
 		}
 
+		// AWS mutates the CIDR block into a network implied by the IP and
+		// mask provided. This results in hashing inconsistencies between
+		// the local config file and the state returned by the API. Error
+		// if the user provides a CIDR block with an inappropriate mask
+		if err := validateCIDRBlock(*add.CIDRBlock); err != nil {
+			return err
+		}
+
 		// Add new Acl entry
-		_, err := conn.CreateNetworkACLEntry(&ec2.CreateNetworkACLEntryInput{
+		_, connErr := conn.CreateNetworkACLEntry(&ec2.CreateNetworkACLEntryInput{
 			NetworkACLID: aws.String(d.Id()),
 			CIDRBlock:    add.CIDRBlock,
 			Egress:       add.Egress,
@@ -294,7 +302,7 @@ func updateNetworkAclEntries(d *schema.ResourceData, entryType string, conn *ec2
 			RuleAction:   add.RuleAction,
 			RuleNumber:   add.RuleNumber,
 		})
-		if err != nil {
+		if connErr != nil {
 			return fmt.Errorf("Error creating %s entry: %s", entryType, err)
 		}
 	}