auth/aws: fix panic in IAM-based login when client config doesn't exist (#23366)

* auth/aws: fix panic in IAM-based login when client config doesn't exist

* add changelog

* adds known issue for 1.15.0

* fixes up known issue with workaround

* fix link

* maintain behavior of client config not needing to exist for IAM login

* update changelog

builtin/credential/aws/backend_test.go

@@ -1504,7 +1504,7 @@ func buildCallerIdentityLoginData(request *http.Request, roleName string) (map[s
 		"iam_request_url":         base64.StdEncoding.EncodeToString([]byte(request.URL.String())),
 		"iam_request_headers":     base64.StdEncoding.EncodeToString(headersJson),
 		"iam_request_body":        base64.StdEncoding.EncodeToString(requestBody),
-		"request_role":            roleName,
+		"role":                    roleName,
 	}, nil
 }
 

builtin/credential/aws/path_login.go

@@ -292,7 +292,7 @@ func (b *backend) pathLoginIamGetRoleNameCallerIdAndEntity(ctx context.Context,
 
 	config, err := b.lockedClientConfigEntry(ctx, req.Storage)
 	if err != nil {
-		return "", nil, nil, logical.ErrorResponse("error getting configuration"), nil
+		return "", nil, nil, nil, fmt.Errorf("error getting configuration: %w", err)
 	}
 
 	endpoint := "https://sts.amazonaws.com"
@@ -319,7 +319,6 @@ func (b *backend) pathLoginIamGetRoleNameCallerIdAndEntity(ctx context.Context,
 		if config.MaxRetries >= 0 {
 			maxRetries = config.MaxRetries
 		}
-	}
 
 		// Extract and use a regional STS endpoint
 		// based on the region set in the Authorization header.
@@ -337,6 +336,7 @@ func (b *backend) pathLoginIamGetRoleNameCallerIdAndEntity(ctx context.Context,
 			b.Logger().Debug("use_sts_region_from_client set; using region specified from header", "region", clientSpecifiedRegion)
 			endpoint = url
 		}
+	}
 
 	b.Logger().Debug("submitting caller identity request", "endpoint", endpoint)
 	callerID, err := submitCallerIdentityRequest(ctx, maxRetries, method, endpoint, parsedUrl, body, headers)

builtin/credential/aws/path_login_test.go

@@ -308,6 +308,56 @@ func TestBackend_validateVaultPostRequestValues(t *testing.T) {
 	}
 }
 
+// TestBackend_pathLogin_NoClientConfig covers logging in via IAM auth when the
+// client config does not exist. This is a regression test to cover potential
+// panics when referencing the potentially-nil config in the login handler. For
+// details see https://github.com/hashicorp/vault/issues/23361.
+func TestBackend_pathLogin_NoClientConfig(t *testing.T) {
+	storage := new(logical.InmemStorage)
+	config := logical.TestBackendConfig()
+	config.StorageView = storage
+	b, err := Backend(config)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = b.Setup(context.Background(), config)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Intentionally left out the client configuration
+
+	roleEntry := &awsRoleEntry{
+		RoleID:   "foo",
+		Version:  currentRoleStorageVersion,
+		AuthType: iamAuthType,
+	}
+	err = b.setRole(context.Background(), storage, testValidRoleName, roleEntry)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	loginData, err := defaultLoginData()
+	if err != nil {
+		t.Fatal(err)
+	}
+	loginRequest := &logical.Request{
+		Operation:  logical.UpdateOperation,
+		Path:       "login",
+		Storage:    storage,
+		Data:       loginData,
+		Connection: &logical.Connection{},
+	}
+	resp, err := b.HandleRequest(context.Background(), loginRequest)
+	if err != nil {
+		t.Fatalf("expected nil error, got: %v", err)
+	}
+	if !resp.IsError() {
+		t.Fatalf("expected error response, got: %+v", resp)
+	}
+}
+
 // TestBackend_pathLogin_IAMHeaders tests login with iam_request_headers,
 // supporting both base64 encoded string and JSON headers
 func TestBackend_pathLogin_IAMHeaders(t *testing.T) {

changelog/23366.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+auth/aws: Fixes a panic that can occur in IAM-based login when a [client config](https://developer.hashicorp.com/vault/api-docs/auth/aws#configure-client) does not exist.
+```

website/content/docs/release-notes/1.15.0.mdx

@@ -16,6 +16,7 @@ description: |-
 Version | Issue
 ------- | -----
 1.15.0+ | [Vault no longer reports rollback metrics by mountpoint](/vault/docs/upgrading/upgrade-to-1.15.x#rollback-metrics)
+1.15.0  | [Panic in AWS auth method during IAM-based login](/vault/docs/upgrading/upgrade-to-1.15.x#panic-in-aws-auth-method-during-iam-based-login)
 
 ## Vault companion updates
 

website/content/docs/upgrading/upgrade-to-1.15.x.mdx

@@ -50,3 +50,5 @@ option.
 @include 'known-issues/transit-managed-keys-panics.mdx'
 
 @include 'known-issues/transit-managed-keys-sign-fails.mdx'
+
+@include 'known-issues/aws-auth-panics.mdx'

website/content/partials/known-issues/aws-auth-panics.mdx

@@ -0,0 +1,18 @@
+### Panic in AWS auth method during IAM-based login
+
+#### Affected versions
+
+- 1.15.0
+
+#### Issue
+
+A panic can occur in the AWS auth method during [IAM-based](/vault/docs/auth/aws#iam-auth-method)
+login when a [client config](/vault/api-docs/auth/aws#configure-client) does not exist.
+
+#### Workaround
+
+The panic can be avoided by writing an empty [client config](/vault/api-docs/auth/aws#configure-client):
+
+```shell-session
+vault write -f auth/aws/config/client
+```