add configs to disable imdsv1 fallback

CHANGELOG_PENDING.md

@@ -1,5 +1,7 @@
 ### SDK Features
 
 ### SDK Enhancements
+* `aws/ec2metadata`: Added environment and shared config support for disabling IMDSv1 fallback.
+  * Use env `AWS_EC2_METADATA_V1_DISABLED` or shared config `ec2_metadata_v1_disabled` accordingly.
 
 ### SDK Bugs

aws/session/env_config.go

@@ -171,6 +171,12 @@ type envConfig struct {
 	// AWS_EC2_METADATA_SERVICE_ENDPOINT_MODE=IPv6
 	EC2IMDSEndpointMode endpoints.EC2IMDSEndpointModeState
 
+	// Specifies that IMDS clients should not fallback to IMDSv1 if token
+	// requests fail.
+	//
+	// AWS_EC2_METADATA_V1_DISABLED=true
+	EC2IMDSv1Disabled *bool
+
 	// Specifies that SDK clients must resolve a dual-stack endpoint for
 	// services.
 	//
@@ -251,6 +257,9 @@ var (
 	ec2IMDSEndpointModeEnvKey = []string{
 		"AWS_EC2_METADATA_SERVICE_ENDPOINT_MODE",
 	}
+	ec2MetadataV1DisabledEnvKey = []string{
+		"AWS_EC2_METADATA_V1_DISABLED",
+	}
 	useCABundleKey = []string{
 		"AWS_CA_BUNDLE",
 	}
@@ -393,6 +402,7 @@ func envConfigLoad(enableSharedConfig bool) (envConfig, error) {
 	if err := setEC2IMDSEndpointMode(&cfg.EC2IMDSEndpointMode, ec2IMDSEndpointModeEnvKey); err != nil {
 		return envConfig{}, err
 	}
+	setBoolPtrFromEnvVal(&cfg.EC2IMDSv1Disabled, ec2MetadataV1DisabledEnvKey)
 
 	if err := setUseDualStackEndpointFromEnvVal(&cfg.UseDualStackEndpoint, awsUseDualStackEndpoint); err != nil {
 		return cfg, err
@@ -414,6 +424,24 @@ func setFromEnvVal(dst *string, keys []string) {
 	}
 }
 
+func setBoolPtrFromEnvVal(dst **bool, keys []string) {
+	for _, k := range keys {
+		value := os.Getenv(k)
+		if len(value) == 0 {
+			continue
+		}
+
+		switch {
+		case strings.EqualFold(value, "false"):
+			*dst = new(bool)
+			**dst = false
+		case strings.EqualFold(value, "true"):
+			*dst = new(bool)
+			**dst = true
+		}
+	}
+}
+
 func setEC2IMDSEndpointMode(mode *endpoints.EC2IMDSEndpointModeState, keys []string) error {
 	for _, k := range keys {
 		value := os.Getenv(k)

aws/session/env_config_test.go

@@ -9,6 +9,7 @@ import (
 	"strconv"
 	"testing"
 
+	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/credentials"
 	"github.com/aws/aws-sdk-go/aws/endpoints"
 	"github.com/aws/aws-sdk-go/awstesting"
@@ -467,6 +468,35 @@ func TestLoadEnvConfig(t *testing.T) {
 			},
 			WantErr: true,
 		},
+		33: {
+			Env: map[string]string{
+				"AWS_EC2_METADATA_V1_DISABLED": "fAlSe",
+			},
+			Config: envConfig{
+				SharedCredentialsFile: shareddefaults.SharedCredentialsFilename(),
+				SharedConfigFile:      shareddefaults.SharedConfigFilename(),
+				EC2IMDSv1Disabled:     aws.Bool(false),
+			},
+		},
+		34: {
+			Env: map[string]string{
+				"AWS_EC2_METADATA_V1_DISABLED": "tRuE",
+			},
+			Config: envConfig{
+				SharedCredentialsFile: shareddefaults.SharedCredentialsFilename(),
+				SharedConfigFile:      shareddefaults.SharedConfigFilename(),
+				EC2IMDSv1Disabled:     aws.Bool(true),
+			},
+		},
+		35: {
+			Env: map[string]string{
+				"AWS_EC2_METADATA_V1_DISABLED": "invalid",
+			},
+			Config: envConfig{
+				SharedCredentialsFile: shareddefaults.SharedCredentialsFilename(),
+				SharedConfigFile:      shareddefaults.SharedConfigFilename(),
+			},
+		},
 	}
 
 	for i, c := range cases {

aws/session/session.go

@@ -779,6 +779,14 @@ func mergeConfigSrcs(cfg, userCfg *aws.Config,
 		cfg.EndpointResolver = wrapEC2IMDSEndpoint(cfg.EndpointResolver, ec2IMDSEndpoint, endpointMode)
 	}
 
+	cfg.EC2MetadataEnableFallback = userCfg.EC2MetadataEnableFallback
+	if cfg.EC2MetadataEnableFallback == nil && envCfg.EC2IMDSv1Disabled != nil {
+		cfg.EC2MetadataEnableFallback = aws.Bool(!*envCfg.EC2IMDSv1Disabled)
+	}
+	if cfg.EC2MetadataEnableFallback == nil && sharedCfg.EC2IMDSv1Disabled != nil {
+		cfg.EC2MetadataEnableFallback = aws.Bool(!*sharedCfg.EC2IMDSv1Disabled)
+	}
+
 	cfg.S3UseARNRegion = userCfg.S3UseARNRegion
 	if cfg.S3UseARNRegion == nil {
 		cfg.S3UseARNRegion = &envCfg.S3UseARNRegion

aws/session/shared_config.go

@@ -80,6 +80,9 @@ const (
 	// EC2 IMDS Endpoint
 	ec2MetadataServiceEndpointKey = "ec2_metadata_service_endpoint"
 
+	// ECS IMDSv1 disable fallback
+	ec2MetadataV1DisabledKey = "ec2_metadata_v1_disabled"
+
 	// Use DualStack Endpoint Resolution
 	useDualStackEndpoint = "use_dualstack_endpoint"
 
@@ -179,6 +182,12 @@ type sharedConfig struct {
 	// ec2_metadata_service_endpoint=http://fd00:ec2::254
 	EC2IMDSEndpoint string
 
+	// Specifies that IMDS clients should not fallback to IMDSv1 if token
+	// requests fail.
+	//
+	// ec2_metadata_v1_disabled=true
+	EC2IMDSv1Disabled *bool
+
 	// Specifies that SDK clients must resolve a dual-stack endpoint for
 	// services.
 	//
@@ -434,6 +443,7 @@ func (cfg *sharedConfig) setFromIniFile(profile string, file sharedConfigFile, e
 				ec2MetadataServiceEndpointModeKey, file.Filename, err)
 		}
 		updateString(&cfg.EC2IMDSEndpoint, section, ec2MetadataServiceEndpointKey)
+		updateBoolPtr(&cfg.EC2IMDSv1Disabled, section, ec2MetadataV1DisabledKey)
 
 		updateUseDualStackEndpoint(&cfg.UseDualStackEndpoint, section, useDualStackEndpoint)
 

aws/session/shared_config_test.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/credentials"
 	"github.com/aws/aws-sdk-go/aws/endpoints"
 	"github.com/aws/aws-sdk-go/internal/ini"
@@ -411,6 +412,30 @@ func TestLoadSharedConfig(t *testing.T) {
 			Profile:   "sso-session-not-exist",
 			Err:       fmt.Errorf("failed to find SSO session section, sso-session-lost"),
 		},
+		{
+			Filenames: []string{testConfigFilename},
+			Profile:   "ec2-metadata-v1-disabled-false",
+			Expected: sharedConfig{
+				Profile:           "ec2-metadata-v1-disabled-false",
+				EC2IMDSv1Disabled: aws.Bool(false),
+			},
+		},
+		{
+			Filenames: []string{testConfigFilename},
+			Profile:   "ec2-metadata-v1-disabled-true",
+			Expected: sharedConfig{
+				Profile:           "ec2-metadata-v1-disabled-true",
+				EC2IMDSv1Disabled: aws.Bool(true),
+			},
+		},
+		{
+			Filenames: []string{testConfigFilename},
+			Profile:   "ec2-metadata-v1-disabled-invalid",
+			Expected: sharedConfig{
+				Profile:           "ec2-metadata-v1-disabled-invalid",
+				EC2IMDSv1Disabled: aws.Bool(false),
+			},
+		},
 	}
 
 	for i, c := range cases {

aws/session/testdata/shared_config

@@ -203,4 +203,13 @@ sso_registration_scopes = sso:account:access
 region = us-east-1
 sso_session = sso-session-lost
 sso_account_id = 123456789012
-sso_role_name = testRole
+sso_role_name = testRole
+
+[profile ec2-metadata-v1-disabled-false]
+ec2_metadata_v1_disabled=False
+
+[profile ec2-metadata-v1-disabled-true]
+ec2_metadata_v1_disabled=True
+
+[profile ec2-metadata-v1-disabled-invalid]
+ec2_metadata_v1_disabled=invalid