update iam password generation

aws/resource_aws_iam_user_login_profile.go

@@ -1,10 +1,11 @@
 package aws
 
 import (
+	"bytes"
+	"crypto/rand"
 	"fmt"
 	"log"
-	"math/rand"
-	"time"
+	"math/big"
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/awserr"
@@ -40,7 +41,7 @@ func resourceAwsIamUserLoginProfile() *schema.Resource {
 				Type:         schema.TypeInt,
 				Optional:     true,
 				Default:      20,
-				ValidateFunc: validation.IntBetween(4, 128),
+				ValidateFunc: validation.IntBetween(5, 128),
 			},
 
 			"key_fingerprint": {
@@ -55,35 +56,62 @@ func resourceAwsIamUserLoginProfile() *schema.Resource {
 	}
 }
 
-// generatePassword generates a random password of a given length using
-// characters that are likely to satisfy any possible AWS password policy
-// (given sufficient length).
-func generatePassword(length int) string {
-	charsets := []string{
-		"abcdefghijklmnopqrstuvwxyz",
-		"ABCDEFGHIJKLMNOPQRSTUVWXYZ",
-		"012346789",
-		"!@#$%^&*()_+-=[]{}|'",
-	}
+const (
+	charLower   = "abcdefghijklmnopqrstuvwxyz"
+	charUpper   = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+	charNumbers = "0123456789"
+	charSymbols = "!@#$%^&*()_+-=[]{}|'"
+)
 
-	// Use all character sets
-	random := rand.New(rand.NewSource(time.Now().UTC().UnixNano()))
-	components := make(map[int]byte, length)
-	for i := 0; i < length; i++ {
-		charset := charsets[i%len(charsets)]
-		components[i] = charset[random.Intn(len(charset))]
-	}
+// generateIAMPassword generates a random password of a given length, matching the
+// most restrictive iam password policy.
+func generateIAMPassword(length int) string {
+	const charset = charLower + charUpper + charNumbers + charSymbols
 
-	// Randomise the ordering so we don't end up with a predictable
-	// lower case, upper case, numeric, symbol pattern
 	result := make([]byte, length)
-	i := 0
-	for _, b := range components {
-		result[i] = b
-		i = i + 1
+	charsetSize := big.NewInt(int64(len(charset)))
+
+	// rather than trying to artifically add specific characters from each
+	// class to the password to match the policy, we generate passwords
+	// randomly and reject those that don't match.
+	//
+	// Even in the worst case, this tends to take less than 10 tries to find a
+	// matching password. Any sufficiently long password is likely to succeed
+	// on the first try
+	for n := 0; n < 100000; n++ {
+		for i := range result {
+			r, err := rand.Int(rand.Reader, charsetSize)
+			if err != nil {
+				panic(err)
+			}
+			if !r.IsInt64() {
+				panic("rand.Int() not representable as an Int64")
+			}
+
+			result[i] = charset[r.Int64()]
+		}
+
+		if !checkIAMPwdPolicy(result) {
+			continue
+		}
+
+		return string(result)
+	}
+
+	panic("failed to generate acceptable password")
+}
+
+// Check the generated password contains all character classes listed in the
+// IAM password policy.
+func checkIAMPwdPolicy(pass []byte) bool {
+	if !(bytes.ContainsAny(pass, charLower) &&
+		bytes.ContainsAny(pass, charNumbers) &&
+		bytes.ContainsAny(pass, charSymbols) &&
+		bytes.ContainsAny(pass, charUpper)) {
+		return false
 	}
 
-	return string(result)
+	return true
 }
 
 func resourceAwsIamUserLoginProfileCreate(d *schema.ResourceData, meta interface{}) error {
@@ -113,7 +141,8 @@ func resourceAwsIamUserLoginProfileCreate(d *schema.ResourceData, meta interface
 		}
 	}
 
-	initialPassword := generatePassword(passwordLength)
+	initialPassword := generateIAMPassword(passwordLength)
+
 	fingerprint, encrypted, err := encryption.EncryptValue(encryptionKey, initialPassword, "Password")
 	if err != nil {
 		return err

aws/resource_aws_iam_user_login_profile_test.go

@@ -20,6 +20,42 @@ import (
 	"github.com/hashicorp/vault/helper/pgpkeys"
 )
 
+func TestGenerateIAMPassword(t *testing.T) {
+	p := generateIAMPassword(6)
+	if len(p) != 6 {
+		t.Fatalf("expected a 6 character password, got: %q", p)
+	}
+
+	p = generateIAMPassword(128)
+	if len(p) != 128 {
+		t.Fatalf("expected a 128 character password, got: %q", p)
+	}
+}
+
+func TestIAMPasswordPolicyCheck(t *testing.T) {
+	for _, tc := range []struct {
+		pass  string
+		valid bool
+	}{
+		// no symbol
+		{pass: "abCD12", valid: false},
+		// no number
+		{pass: "abCD%$", valid: false},
+		// no upper
+		{pass: "abcd1#", valid: false},
+		// no lower
+		{pass: "ABCD1#", valid: false},
+		{pass: "abCD11#$", valid: true},
+	} {
+		t.Run(tc.pass, func(t *testing.T) {
+			valid := checkIAMPwdPolicy([]byte(tc.pass))
+			if valid != tc.valid {
+				t.Fatalf("expected %q to be valid==%t, got %t", tc.pass, tc.valid, valid)
+			}
+		})
+	}
+}
+
 func TestAccAWSUserLoginProfile_basic(t *testing.T) {
 	var conf iam.GetLoginProfileOutput
 
@@ -189,7 +225,7 @@ func testDecryptPasswordAndTest(nProfile, nAccessKey, key string) resource.TestC
 			iamAsCreatedUser := iam.New(iamAsCreatedUserSession)
 			_, err = iamAsCreatedUser.ChangePassword(&iam.ChangePasswordInput{
 				OldPassword: aws.String(decryptedPassword.String()),
-				NewPassword: aws.String(generatePassword(20)),
+				NewPassword: aws.String(generateIAMPassword(20)),
 			})
 			if err != nil {
 				if awserr, ok := err.(awserr.Error); ok && awserr.Code() == "InvalidClientTokenId" {