backend.go

package awsauth

import (
	"fmt"
	"sync"
	"time"

	"github.com/aws/aws-sdk-go/aws/endpoints"
	"github.com/aws/aws-sdk-go/service/ec2"
	"github.com/aws/aws-sdk-go/service/iam"
	"github.com/hashicorp/vault/logical"
	"github.com/hashicorp/vault/logical/framework"
	"github.com/patrickmn/go-cache"
)

func Factory(conf *logical.BackendConfig) (logical.Backend, error) {
	b, err := Backend(conf)
	if err != nil {
		return nil, err
	}
	if err := b.Setup(conf); err != nil {
		return nil, err
	}
	return b, nil
}

type backend struct {
	*framework.Backend

	// Lock to make changes to any of the backend's configuration endpoints.
	configMutex sync.RWMutex

	// Lock to make changes to role entries
	roleMutex sync.RWMutex

	// Lock to make changes to the blacklist entries
	blacklistMutex sync.RWMutex

	// Guards the blacklist/whitelist tidy functions
	tidyBlacklistCASGuard uint32
	tidyWhitelistCASGuard uint32

	// Duration after which the periodic function of the backend needs to
	// tidy the blacklist and whitelist entries.
	tidyCooldownPeriod time.Duration

	// nextTidyTime holds the time at which the periodic func should initiatite
	// the tidy operations. This is set by the periodicFunc based on the value
	// of tidyCooldownPeriod.
	nextTidyTime time.Time

	// Map to hold the EC2 client objects indexed by region and STS role.
	// This avoids the overhead of creating a client object for every login request.
	// When the credentials are modified or deleted, all the cached client objects
	// will be flushed. The empty STS role signifies the master account
	EC2ClientsMap map[string]map[string]*ec2.EC2

	// Map to hold the IAM client objects indexed by region and STS role.
	// This avoids the overhead of creating a client object for every login request.
	// When the credentials are modified or deleted, all the cached client objects
	// will be flushed. The empty STS role signifies the master account
	IAMClientsMap map[string]map[string]*iam.IAM

	// Map of AWS unique IDs to the full ARN corresponding to that unique ID
	// This avoids the overhead of an AWS API hit for every login request
	// using the IAM auth method when bound_iam_principal_arn contains a wildcard
	iamUserIdToArnCache *cache.Cache

	// AWS Account ID of the "default" AWS credentials
	// This cache avoids the need to call GetCallerIdentity repeatedly to learn it
	// We can't store this because, in certain pathological cases, it could change
	// out from under us, such as a standby and active Vault server in different AWS
	// accounts using their IAM instance profile to get their credentials.
	defaultAWSAccountID string

	resolveArnToUniqueIDFunc func(logical.Storage, string) (string, error)
}

func Backend(conf *logical.BackendConfig) (*backend, error) {
	b := &backend{
		// Setting the periodic func to be run once in an hour.
		// If there is a real need, this can be made configurable.
		tidyCooldownPeriod:  time.Hour,
		EC2ClientsMap:       make(map[string]map[string]*ec2.EC2),
		IAMClientsMap:       make(map[string]map[string]*iam.IAM),
		iamUserIdToArnCache: cache.New(7*24*time.Hour, 24*time.Hour),
	}

	b.resolveArnToUniqueIDFunc = b.resolveArnToRealUniqueId

	b.Backend = &framework.Backend{
		PeriodicFunc: b.periodicFunc,
		AuthRenew:    b.pathLoginRenew,
		Help:         backendHelp,
		PathsSpecial: &logical.Paths{
			Unauthenticated: []string{
				"login",
			},
			LocalStorage: []string{
				"whitelist/identity/",
			},
		},
		Paths: []*framework.Path{
			pathLogin(b),
			pathListRole(b),
			pathListRoles(b),
			pathRole(b),
			pathRoleTag(b),
			pathConfigClient(b),
			pathConfigCertificate(b),
			pathConfigSts(b),
			pathListSts(b),
			pathConfigTidyRoletagBlacklist(b),
			pathConfigTidyIdentityWhitelist(b),
			pathListCertificates(b),
			pathListRoletagBlacklist(b),
			pathRoletagBlacklist(b),
			pathTidyRoletagBlacklist(b),
			pathListIdentityWhitelist(b),
			pathIdentityWhitelist(b),
			pathTidyIdentityWhitelist(b),
		},
		Invalidate:  b.invalidate,
		BackendType: logical.TypeCredential,
	}

	return b, nil
}

// periodicFunc performs the tasks that the backend wishes to do periodically.
// Currently this will be triggered once in a minute by the RollbackManager.
//
// The tasks being done currently by this function are to cleanup the expired
// entries of both blacklist role tags and whitelist identities. Tidying is done
// not once in a minute, but once in an hour, controlled by 'tidyCooldownPeriod'.
// Tidying of blacklist and whitelist are by default enabled. This can be
// changed using `config/tidy/roletags` and `config/tidy/identities` endpoints.
func (b *backend) periodicFunc(req *logical.Request) error {
	// Run the tidy operations for the first time. Then run it when current
	// time matches the nextTidyTime.
	if b.nextTidyTime.IsZero() || !time.Now().Before(b.nextTidyTime) {
		// safety_buffer defaults to 180 days for roletag blacklist
		safety_buffer := 15552000
		tidyBlacklistConfigEntry, err := b.lockedConfigTidyRoleTags(req.Storage)
		if err != nil {
			return err
		}
		skipBlacklistTidy := false
		// check if tidying of role tags was configured
		if tidyBlacklistConfigEntry != nil {
			// check if periodic tidying of role tags was disabled
			if tidyBlacklistConfigEntry.DisablePeriodicTidy {
				skipBlacklistTidy = true
			}
			// overwrite the default safety_buffer with the configured value
			safety_buffer = tidyBlacklistConfigEntry.SafetyBuffer
		}
		// tidy role tags if explicitly not disabled
		if !skipBlacklistTidy {
			b.tidyBlacklistRoleTag(req.Storage, safety_buffer)
		}

		// reset the safety_buffer to 72h
		safety_buffer = 259200
		tidyWhitelistConfigEntry, err := b.lockedConfigTidyIdentities(req.Storage)
		if err != nil {
			return err
		}
		skipWhitelistTidy := false
		// check if tidying of identities was configured
		if tidyWhitelistConfigEntry != nil {
			// check if periodic tidying of identities was disabled
			if tidyWhitelistConfigEntry.DisablePeriodicTidy {
				skipWhitelistTidy = true
			}
			// overwrite the default safety_buffer with the configured value
			safety_buffer = tidyWhitelistConfigEntry.SafetyBuffer
		}
		// tidy identities if explicitly not disabled
		if !skipWhitelistTidy {
			b.tidyWhitelistIdentity(req.Storage, safety_buffer)
		}

		// Update the time at which to run the tidy functions again.
		b.nextTidyTime = time.Now().Add(b.tidyCooldownPeriod)
	}
	return nil
}

func (b *backend) invalidate(key string) {
	switch key {
	case "config/client":
		b.configMutex.Lock()
		defer b.configMutex.Unlock()
		b.flushCachedEC2Clients()
		b.flushCachedIAMClients()
		b.defaultAWSAccountID = ""
	}
}

// Putting this here so we can inject a fake resolver into the backend for unit testing
// purposes
func (b *backend) resolveArnToRealUniqueId(s logical.Storage, arn string) (string, error) {
	entity, err := parseIamArn(arn)
	if err != nil {
		return "", err
	}
	// This odd-looking code is here because IAM is an inherently global service. IAM and STS ARNs
	// don't have regions in them, and there is only a single global endpoint for IAM; see
	// http://docs.aws.amazon.com/general/latest/gr/rande.html#iam_region
	// However, the ARNs do have a partition in them, because the GovCloud and China partitions DO
	// have their own separate endpoints, and the partition is encoded in the ARN. If Amazon's Go SDK
	// would allow us to pass a partition back to the IAM client, it would be much simpler. But it
	// doesn't appear that's possible, so in order to properly support GovCloud and China, we do a
	// circular dance of extracting the partition from the ARN, finding any arbitrary region in the
	// partition, and passing that region back back to the SDK, so that the SDK can figure out the
	// proper partition from the arbitrary region we passed in to look up the endpoint.
	// Sigh
	region := getAnyRegionForAwsPartition(entity.Partition)
	if region == nil {
		return "", fmt.Errorf("Unable to resolve partition %q to a region", entity.Partition)
	}
	iamClient, err := b.clientIAM(s, region.ID(), entity.AccountNumber)
	if err != nil {
		return "", err
	}

	switch entity.Type {
	case "user":
		userInfo, err := iamClient.GetUser(&iam.GetUserInput{UserName: &entity.FriendlyName})
		if err != nil {
			return "", err
		}
		if userInfo == nil {
			return "", fmt.Errorf("got nil result from GetUser")
		}
		return *userInfo.User.UserId, nil
	case "role":
		roleInfo, err := iamClient.GetRole(&iam.GetRoleInput{RoleName: &entity.FriendlyName})
		if err != nil {
			return "", err
		}
		if roleInfo == nil {
			return "", fmt.Errorf("got nil result from GetRole")
		}
		return *roleInfo.Role.RoleId, nil
	case "instance-profile":
		profileInfo, err := iamClient.GetInstanceProfile(&iam.GetInstanceProfileInput{InstanceProfileName: &entity.FriendlyName})
		if err != nil {
			return "", err
		}
		if profileInfo == nil {
			return "", fmt.Errorf("got nil result from GetInstanceProfile")
		}
		return *profileInfo.InstanceProfile.InstanceProfileId, nil
	default:
		return "", fmt.Errorf("unrecognized error type %#v", entity.Type)
	}
}

// Adapted from https://docs.aws.amazon.com/sdk-for-go/api/aws/endpoints/
// the "Enumerating Regions and Endpoint Metadata" section
func getAnyRegionForAwsPartition(partitionId string) *endpoints.Region {
	resolver := endpoints.DefaultResolver()
	partitions := resolver.(endpoints.EnumPartitions).Partitions()

	for _, p := range partitions {
		if p.ID() == partitionId {
			for _, r := range p.Regions() {
				return &r
			}
		}
	}
	return nil
}

const backendHelp = `
aws-ec2 auth backend takes in PKCS#7 signature of an AWS EC2 instance and a client
created nonce to authenticates the EC2 instance with Vault.

Authentication is backed by a preconfigured role in the backend. The role
represents the authorization of resources by containing Vault's policies.
Role can be created using 'role/<role>' endpoint.

If there is need to further restrict the capabilities of the role on the instance
that is using the role, 'role_tag' option can be enabled on the role, and a tag
can be generated using 'role/<role>/tag' endpoint. This tag represents the
subset of capabilities set on the role. When the 'role_tag' option is enabled on
the role, the login operation requires that a respective role tag is attached to
the EC2 instance which performs the login.
`