feat: add env support for disabling v1 fallback

.changelog/99f6ee13815544af9c5dcf4c6fcd6453.json

@@ -0,0 +1,8 @@
+{
+    "id": "99f6ee13-8155-44af-9c5d-cf4c6fcd6453",
+    "type": "feature",
+    "description": "Add env and shared config settings for disabling IMDSv1 fallback.",
+    "modules": [
+        "config"
+    ]
+}

config/env_config.go

@@ -57,7 +57,8 @@ const (
 
 	awsEc2MetadataServiceEndpointEnvVar = "AWS_EC2_METADATA_SERVICE_ENDPOINT"
 
-	awsEc2MetadataDisabled = "AWS_EC2_METADATA_DISABLED"
+	awsEc2MetadataDisabled         = "AWS_EC2_METADATA_DISABLED"
+	awsEc2MetadataV1DisabledEnvVar = "AWS_EC2_METADATA_V1_DISABLED"
 
 	awsS3DisableMultiRegionAccessPointEnvVar = "AWS_S3_DISABLE_MULTIREGION_ACCESS_POINTS"
 
@@ -209,6 +210,11 @@ type EnvConfig struct {
 	// AWS_EC2_METADATA_DISABLED=true
 	EC2IMDSClientEnableState imds.ClientEnableState
 
+	// Specifies if EC2 IMDSv1 fallback is disabled.
+	//
+	// AWS_EC2_METADATA_V1_DISABLED=true
+	EC2IMDSv1Disabled *bool
+
 	// Specifies the EC2 Instance Metadata Service default endpoint selection mode (IPv4 or IPv6)
 	//
 	// AWS_EC2_METADATA_SERVICE_ENDPOINT_MODE=IPv6
@@ -317,6 +323,9 @@ func NewEnvConfig() (EnvConfig, error) {
 		return cfg, err
 	}
 	cfg.EC2IMDSEndpoint = os.Getenv(awsEc2MetadataServiceEndpointEnvVar)
+	if err := setBoolPtrFromEnvVal(&cfg.EC2IMDSv1Disabled, []string{awsEc2MetadataV1DisabledEnvVar}); err != nil {
+		return cfg, err
+	}
 
 	if err := setBoolPtrFromEnvVal(&cfg.S3DisableMultiRegionAccessPoints, []string{awsS3DisableMultiRegionAccessPointEnvVar}); err != nil {
 		return cfg, err
@@ -717,3 +726,13 @@ func (c EnvConfig) GetEC2IMDSEndpoint() (string, bool, error) {
 
 	return c.EC2IMDSEndpoint, true, nil
 }
+
+// GetEC2IMDSV1FallbackDisabled implements an EC2IMDSV1FallbackDisabled option
+// resolver interface.
+func (c EnvConfig) GetEC2IMDSV1FallbackDisabled() (bool, bool) {
+	if c.EC2IMDSv1Disabled == nil {
+		return false, false
+	}
+
+	return *c.EC2IMDSv1Disabled, true
+}

config/env_config_test.go

@@ -439,6 +439,23 @@ func TestNewEnvConfig(t *testing.T) {
 				IgnoreConfiguredEndpoints: ptr.Bool(true),
 			},
 		},
+		40: {
+			Env: map[string]string{
+				"AWS_EC2_METADATA_V1_DISABLED": "tRuE",
+			},
+			Config: EnvConfig{
+				EC2IMDSv1Disabled: aws.Bool(true),
+			},
+		},
+		41: {
+			Env: map[string]string{
+				"AWS_EC2_METADATA_V1_DISABLED": "invalid",
+			},
+			Config: EnvConfig{
+				EC2IMDSv1Disabled: aws.Bool(false), // setBoolPtrFromEnvVal new()s the bool even if it errors
+			},
+			WantErr: true,
+		},
 	}
 
 	for i, c := range cases {

config/shared_config.go

@@ -79,6 +79,8 @@ const (
 
 	ec2MetadataServiceEndpointKey = "ec2_metadata_service_endpoint"
 
+	ec2MetadataV1DisabledKey = "ec2_metadata_v1_disabled"
+
 	// Use DualStack Endpoint Resolution
 	useDualStackEndpoint = "use_dualstack_endpoint"
 
@@ -246,6 +248,12 @@ 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 if the S3 service should disable support for Multi-Region
 	// access-points
 	//
@@ -397,6 +405,16 @@ func (c SharedConfig) GetEC2IMDSEndpoint() (string, bool, error) {
 	return c.EC2IMDSEndpoint, true, nil
 }
 
+// GetEC2IMDSV1FallbackDisabled implements an EC2IMDSV1FallbackDisabled option
+// resolver interface.
+func (c SharedConfig) GetEC2IMDSV1FallbackDisabled() (bool, bool) {
+	if c.EC2IMDSv1Disabled == nil {
+		return false, false
+	}
+
+	return *c.EC2IMDSv1Disabled, true
+}
+
 // GetUseDualStackEndpoint returns whether the service's dual-stack endpoint should be
 // used for requests.
 func (c SharedConfig) GetUseDualStackEndpoint(ctx context.Context) (value aws.DualStackEndpointState, found bool, err error) {
@@ -807,6 +825,7 @@ func mergeSections(dst *ini.Sections, src ini.Sections) error {
 			s3DisableMultiRegionAccessPointsKey,
 			ec2MetadataServiceEndpointModeKey,
 			ec2MetadataServiceEndpointKey,
+			ec2MetadataV1DisabledKey,
 			useDualStackEndpoint,
 			useFIPSEndpointKey,
 			defaultsModeKey,
@@ -1040,6 +1059,7 @@ func (c *SharedConfig) setFromIniSection(profile string, section ini.Section) er
 		return fmt.Errorf("failed to load %s from shared config, %v", ec2MetadataServiceEndpointModeKey, err)
 	}
 	updateString(&c.EC2IMDSEndpoint, section, ec2MetadataServiceEndpointKey)
+	updateBoolPtr(&c.EC2IMDSv1Disabled, section, ec2MetadataV1DisabledKey)
 
 	updateUseDualStackEndpoint(&c.UseDualStackEndpoint, section, useDualStackEndpoint)
 	updateUseFIPSEndpoint(&c.UseFIPSEndpoint, section, useFIPSEndpointKey)

config/shared_config_test.go

@@ -660,7 +660,32 @@ func TestNewSharedConfig(t *testing.T) {
 				BaseEndpoint:              "https://example.com",
 				IgnoreConfiguredEndpoints: ptr.Bool(true),
 			},
-		}}
+		},
+		"imdsv1 disabled = false": {
+			ConfigFilenames: []string{testConfigFilename},
+			Profile:         "ec2-metadata-v1-disabled-false",
+			Expected: SharedConfig{
+				Profile:           "ec2-metadata-v1-disabled-false",
+				EC2IMDSv1Disabled: aws.Bool(false),
+			},
+		},
+		"imdsv1 disabled = true": {
+			ConfigFilenames: []string{testConfigFilename},
+			Profile:         "ec2-metadata-v1-disabled-true",
+			Expected: SharedConfig{
+				Profile:           "ec2-metadata-v1-disabled-true",
+				EC2IMDSv1Disabled: aws.Bool(true),
+			},
+		},
+		"imdsv1 disabled = invalid": {
+			ConfigFilenames: []string{testConfigFilename},
+			Profile:         "ec2-metadata-v1-disabled-invalid",
+			Expected: SharedConfig{
+				Profile:           "ec2-metadata-v1-disabled-invalid",
+				EC2IMDSv1Disabled: aws.Bool(false),
+			},
+		},
+	}
 
 	for name, c := range cases {
 		t.Run(name, func(t *testing.T) {

config/testdata/shared_config

@@ -282,3 +282,12 @@ sdk_ua_app_id = 12345
 [profile endpoint_config]
 ignore_configured_endpoint_urls = true
 endpoint_url = https://example.com
+
+[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

feature/ec2/imds/api_client.go

@@ -119,6 +119,7 @@ func NewFromConfig(cfg aws.Config, optFns ...func(*Options)) *Client {
 	resolveClientEnableState(cfg, &opts)
 	resolveEndpointConfig(cfg, &opts)
 	resolveEndpointModeConfig(cfg, &opts)
+	resolveEnableFallback(cfg, &opts)
 
 	return New(opts, optFns...)
 }
@@ -328,3 +329,20 @@ func resolveEndpointConfig(cfg aws.Config, options *Options) error {
 	options.Endpoint = value
 	return nil
 }
+
+func resolveEnableFallback(cfg aws.Config, options *Options) {
+	if options.EnableFallback != aws.UnknownTernary {
+		return
+	}
+
+	disabled, ok := internalconfig.ResolveV1FallbackDisabled(cfg.ConfigSources)
+	if !ok {
+		return
+	}
+
+	if disabled {
+		options.EnableFallback = aws.FalseTernary
+	} else {
+		options.EnableFallback = aws.TrueTernary
+	}
+}

feature/ec2/imds/internal/config/resolvers.go

@@ -58,6 +58,10 @@ type EndpointResolver interface {
 	GetEC2IMDSEndpoint() (string, bool, error)
 }
 
+type v1FallbackDisabledResolver interface {
+	GetEC2IMDSV1FallbackDisabled() (bool, bool)
+}
+
 // ResolveClientEnableState resolves the ClientEnableState from a list of configuration sources.
 func ResolveClientEnableState(sources []interface{}) (value ClientEnableState, found bool, err error) {
 	for _, source := range sources {
@@ -96,3 +100,15 @@ func ResolveEndpointConfig(sources []interface{}) (value string, found bool, err
 	}
 	return value, found, err
 }
+
+// ResolveV1FallbackDisabled ...
+func ResolveV1FallbackDisabled(sources []interface{}) (bool, bool) {
+	for _, source := range sources {
+		if resolver, ok := source.(v1FallbackDisabledResolver); ok {
+			if v, found := resolver.GetEC2IMDSV1FallbackDisabled(); found {
+				return v, true
+			}
+		}
+	}
+	return false, false
+}