acls.go

package headscale

import (
	"errors"
	"fmt"
	"net/netip"
	"strconv"
	"strings"
	"time"

	"github.com/rs/zerolog/log"
	"github.com/samber/lo"
	"go4.org/netipx"
	"tailscale.com/tailcfg"
)

const (
	errEmptyPolicy       = Error("empty policy")
	errInvalidAction     = Error("invalid action")
	errInvalidGroup      = Error("invalid group")
	errInvalidTag        = Error("invalid tag")
	errInvalidPortFormat = Error("invalid port format")
	errWildcardIsNeeded  = Error("wildcard as port is required for the protocol")
)

const (
	Base8              = 8
	Base10             = 10
	BitSize16          = 16
	BitSize32          = 32
	BitSize64          = 64
	portRangeBegin     = 0
	portRangeEnd       = 65535
	expectedTokenItems = 2
)

// For some reason golang.org/x/net/internal/iana is an internal package.
const (
	protocolICMP     = 1   // Internet Control Message
	protocolIGMP     = 2   // Internet Group Management
	protocolIPv4     = 4   // IPv4 encapsulation
	protocolTCP      = 6   // Transmission Control
	protocolEGP      = 8   // Exterior Gateway Protocol
	protocolIGP      = 9   // any private interior gateway (used by Cisco for their IGRP)
	protocolUDP      = 17  // User Datagram
	protocolGRE      = 47  // Generic Routing Encapsulation
	protocolESP      = 50  // Encap Security Payload
	protocolAH       = 51  // Authentication Header
	protocolIPv6ICMP = 58  // ICMP for IPv6
	protocolSCTP     = 132 // Stream Control Transmission Protocol
	ProtocolFC       = 133 // Fibre Channel
)

// UserACLPolicy is a group of acl rules to manage access between devices of a single user.
type UserACLPolicy struct {
	ID uint64 `gorm:"primary_key"`

	UserID uint `gorm:"unique"`
	User   User `gorm:"foreignKey:UserID"`

	ACLPolicy ACLPolicy `gorm:"json"`

	CreatedAt time.Time
	UpdatedAt time.Time
}

// generateACLPeerCacheMap takes a list of Tailscale filter rules and generates a map
// of which Sources ("*" and IPs) can access destinations. This is to speed up the
// process of generating MapResponses when deciding which Peers to inform nodes about.
func generateACLPeerCacheMap(
	rules []tailcfg.FilterRule,
) map[string]map[string]struct{} {
	aclCachePeerMap := make(map[string]map[string]struct{})
	for _, rule := range rules {
		for _, srcIP := range rule.SrcIPs {
			for _, ip := range expandACLPeerAddr(srcIP) {
				if data, ok := aclCachePeerMap[ip]; ok {
					for _, dstPort := range rule.DstPorts {
						for _, dstIP := range expandACLPeerAddr(dstPort.IP) {
							data[dstIP] = struct{}{}
						}
					}
				} else {
					dstPortsMap := make(map[string]struct{}, len(rule.DstPorts))
					for _, dstPort := range rule.DstPorts {
						for _, dstIP := range expandACLPeerAddr(dstPort.IP) {
							dstPortsMap[dstIP] = struct{}{}
						}
					}
					aclCachePeerMap[ip] = dstPortsMap
				}
			}
		}
	}

	log.Trace().
		Interface("ACL Cache Map", aclCachePeerMap).
		Msg("ACL Peer Cache Map generated")

	return aclCachePeerMap
}

// expandACLPeerAddr takes a "tailcfg.FilterRule" "IP" and expands it into
// something our cache logic can look up, which is "*" or single IP addresses.
// This is probably quite inefficient, but it is a result of
// "make it work, then make it fast", and a lot of the ACL stuff does not
// work, but people have tried to make it fast.
func expandACLPeerAddr(srcIP string) []string {
	if ip, err := netip.ParseAddr(srcIP); err == nil {
		return []string{ip.String()}
	}

	if cidr, err := netip.ParsePrefix(srcIP); err == nil {
		addrs := []string{}

		ipRange := netipx.RangeOfPrefix(cidr)

		from := ipRange.From()
		too := ipRange.To()

		if from == too {
			return []string{from.String()}
		}

		for from != too && from.Less(too) {
			addrs = append(addrs, from.String())
			from = from.Next()
		}
		addrs = append(addrs, too.String()) // Add the last IP address in the range

		return addrs
	}

	// probably "*" or other string based "IP"
	return []string{srcIP}
}

func (h *Headscale) getACLRules(machine Machine) ([]tailcfg.FilterRule, error) {
	machines, err := h.ListMachinesByUserID(machine.UserID)
	if err != nil {
		return nil, err
	}
	policy, err := h.getACLPolicy(machine.UserID)
	if err != nil {
		return nil, err
	}

	rules, err := generateACLRules(machines, policy)
	if err != nil {
		return nil, err
	}

	return rules, nil
}

func (h *Headscale) getACLPolicy(userID uint) (ACLPolicy, error) {
	var policy UserACLPolicy
	if err := h.db.
		Where("user_id = ?", userID).FirstOrInit(&policy).Error; err != nil {
		log.Error().Err(err).Msg("Error accessing db")

		return ACLPolicy{}, fmt.Errorf("unable to query acl policy: %w", err)
	}

	return policy.ACLPolicy, nil
}

func generateACLRules(
	machines []Machine,
	aclPolicy ACLPolicy,
) ([]tailcfg.FilterRule, error) {
	rules := []tailcfg.FilterRule{}

	for index, acl := range aclPolicy.ACLs {
		if acl.Action != "accept" {
			return nil, errInvalidAction
		}

		srcIPs := []string{}
		for innerIndex, src := range acl.Sources {
			srcs, err := generateACLPolicySrc(machines, aclPolicy, src)
			if err != nil {
				log.Error().
					Msgf("Error parsing ACL %d, Source %d", index, innerIndex)

				return nil, err
			}
			srcIPs = append(srcIPs, srcs...)
		}

		protocols, needsWildcard, err := parseProtocol(acl.Protocol)
		if err != nil {
			log.Error().
				Msgf("Error parsing ACL %d. protocol unknown %s", index, acl.Protocol)

			return nil, err
		}

		destPorts := []tailcfg.NetPortRange{}
		for innerIndex, dest := range acl.Destinations {
			dests, err := generateACLPolicyDest(
				machines,
				aclPolicy,
				dest,
				needsWildcard,
			)
			if err != nil {
				log.Error().
					Msgf("Error parsing ACL %d, Destination %d", index, innerIndex)

				return nil, err
			}
			destPorts = append(destPorts, dests...)
		}

		rules = append(rules, tailcfg.FilterRule{
			SrcIPs:   srcIPs,
			DstPorts: destPorts,
			IPProto:  protocols,
		})
	}

	log.Trace().
		Any("aclPolicy", aclPolicy).
		Any("rules", rules).
		Msg("generated tailcfg rules")

	return rules, nil
}

//nolint:unused
func (h *Headscale) generateSSHRules(policy *ACLPolicy) ([]*tailcfg.SSHRule, error) {
	rules := []*tailcfg.SSHRule{}

	if policy == nil {
		return nil, errEmptyPolicy
	}

	machines, err := h.ListMachines()
	if err != nil {
		return nil, err
	}

	acceptAction := tailcfg.SSHAction{
		Message:                  "",
		Reject:                   false,
		Accept:                   true,
		SessionDuration:          0,
		AllowAgentForwarding:     false,
		HoldAndDelegate:          "",
		AllowLocalPortForwarding: true,
	}

	rejectAction := tailcfg.SSHAction{
		Message:                  "",
		Reject:                   true,
		Accept:                   false,
		SessionDuration:          0,
		AllowAgentForwarding:     false,
		HoldAndDelegate:          "",
		AllowLocalPortForwarding: false,
	}

	for index, sshACL := range policy.SSHs {
		action := rejectAction
		switch sshACL.Action {
		case "accept":
			action = acceptAction
		case "check":
			checkAction, err := sshCheckAction(sshACL.CheckPeriod)
			if err != nil {
				log.Error().
					Msgf("Error parsing SSH %d, check action with unparsable duration '%s'", index, sshACL.CheckPeriod)
			} else {
				action = *checkAction
			}
		default:
			log.Error().
				Msgf("Error parsing SSH %d, unknown action '%s'", index, sshACL.Action)

			return nil, err
		}

		principals := make([]*tailcfg.SSHPrincipal, 0, len(sshACL.Sources))
		for innerIndex, rawSrc := range sshACL.Sources {
			expandedSrcs, err := expandAlias(machines, *policy, rawSrc)
			if err != nil {
				log.Error().
					Msgf("Error parsing SSH %d, Source %d", index, innerIndex)

				return nil, err
			}
			for _, expandedSrc := range expandedSrcs {
				principals = append(principals, &tailcfg.SSHPrincipal{
					NodeIP: expandedSrc,
				})
			}
		}

		userMap := make(map[string]string, len(sshACL.Users))
		for _, user := range sshACL.Users {
			userMap[user] = "="
		}
		rules = append(rules, &tailcfg.SSHRule{
			RuleExpires: nil,
			Principals:  principals,
			SSHUsers:    userMap,
			Action:      &action,
		})
	}

	return rules, nil
}

// CreateOrUpdateUserACLPolicy creates an acl policy for the given user.
func (h *Headscale) CreateOrUpdateUserACLPolicy(
	userID uint,
	policy ACLPolicy,
) (*UserACLPolicy, error) {
	existingUserPolicy := UserACLPolicy{UserID: userID}
	if err := h.db.Where("user_id = ?", userID).First(&existingUserPolicy).Error; err == nil {
		// already exists, just update
		existingUserPolicy.ACLPolicy = policy
		if err := h.db.Save(&existingUserPolicy).Error; err != nil {
			log.Error().
				Str("func", "CreateOrUpdateUserACLPolicy").
				Err(err).
				Msg("Could not update user acl policy")

			return nil, err
		}

		return &existingUserPolicy, nil
	}

	userACLPolicy := UserACLPolicy{ACLPolicy: policy, UserID: userID}
	if err := h.db.Create(&userACLPolicy).Error; err != nil {
		log.Error().
			Str("func", "CreateOrUpdateUserACLPolicy").
			Err(err).
			Msg("Could not create user acl policy")

		return nil, err
	}

	return &userACLPolicy, nil
}

// DestroyUserACLPolicy destroys a acl policy for a given user if it exists.
func (h *Headscale) DestroyUserACLPolicy(userID uint) error {
	if result := h.db.Unscoped().Where(
		"user_id = ?", userID).Delete(&UserACLPolicy{}); result.Error != nil {
		return result.Error
	}

	return nil
}

//nolint:unused
func sshCheckAction(duration string) (*tailcfg.SSHAction, error) {
	sessionLength, err := time.ParseDuration(duration)
	if err != nil {
		return nil, err
	}

	return &tailcfg.SSHAction{
		Message:                  "",
		Reject:                   false,
		Accept:                   true,
		SessionDuration:          sessionLength,
		AllowAgentForwarding:     false,
		HoldAndDelegate:          "",
		AllowLocalPortForwarding: true,
	}, nil
}

func generateACLPolicySrc(
	machines []Machine,
	aclPolicy ACLPolicy,
	src string,
) ([]string, error) {
	return expandAlias(machines, aclPolicy, src)
}

func generateACLPolicyDest(
	machines []Machine,
	aclPolicy ACLPolicy,
	dest string,
	needsWildcard bool,
) ([]tailcfg.NetPortRange, error) {
	var tokens []string

	log.Trace().Str("destination", dest).Msg("generating policy destination")

	// Check if there is a IPv4/6:Port combination, IPv6 has more than
	// three ":".
	tokens = strings.Split(dest, ":")
	if len(tokens) < expectedTokenItems || len(tokens) > 3 {
		port := tokens[len(tokens)-1]

		maybeIPv6Str := strings.TrimSuffix(dest, ":"+port)
		log.Trace().Str("maybeIPv6Str", maybeIPv6Str).Msg("")

		if maybeIPv6, err := netip.ParseAddr(maybeIPv6Str); err != nil &&
			!maybeIPv6.Is6() {
			log.Trace().Err(err).Msg("trying to parse as IPv6")

			return nil, fmt.Errorf(
				"failed to parse destination, tokens %v: %w",
				tokens,
				errInvalidPortFormat,
			)
		} else {
			tokens = []string{maybeIPv6Str, port}
		}
	}

	log.Trace().Strs("tokens", tokens).Msg("generating policy destination")

	var alias string
	// We can have here stuff like:
	// git-server:*
	// 192.168.1.0/24:22
	// fd7a:115c:a1e0::2:22
	// fd7a:115c:a1e0::2/128:22
	// tag:montreal-webserver:80,443
	// tag:api-server:443
	// example-host-1:*
	if len(tokens) == expectedTokenItems {
		alias = tokens[0]
	} else {
		alias = fmt.Sprintf("%s:%s", tokens[0], tokens[1])
	}

	expanded, err := expandAlias(machines, aclPolicy, alias)
	if err != nil {
		return nil, err
	}
	ports, err := expandPorts(tokens[len(tokens)-1], needsWildcard)
	if err != nil {
		return nil, err
	}

	dests := []tailcfg.NetPortRange{}
	for _, d := range expanded {
		for _, p := range *ports {
			pr := tailcfg.NetPortRange{
				IP:    d,
				Ports: p,
			}
			dests = append(dests, pr)
		}
	}

	return dests, nil
}

// parseProtocol reads the proto field of the ACL and generates a list of
// protocols that will be allowed, following the IANA IP protocol number
// https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml
//
// If the ACL proto field is empty, it allows ICMPv4, ICMPv6, TCP, and UDP,
// as per Tailscale behaviour (see tailcfg.FilterRule).
//
// Also returns a boolean indicating if the protocol
// requires all the destinations to use wildcard as port number (only TCP,
// UDP and SCTP support specifying ports).
func parseProtocol(protocol string) ([]int, bool, error) {
	switch protocol {
	case "":
		return nil, false, nil
	case "igmp":
		return []int{protocolIGMP}, true, nil
	case "ipv4", "ip-in-ip":
		return []int{protocolIPv4}, true, nil
	case "tcp":
		return []int{protocolTCP}, false, nil
	case "egp":
		return []int{protocolEGP}, true, nil
	case "igp":
		return []int{protocolIGP}, true, nil
	case "udp":
		return []int{protocolUDP}, false, nil
	case "gre":
		return []int{protocolGRE}, true, nil
	case "esp":
		return []int{protocolESP}, true, nil
	case "ah":
		return []int{protocolAH}, true, nil
	case "sctp":
		return []int{protocolSCTP}, false, nil
	case "icmp":
		return []int{protocolICMP, protocolIPv6ICMP}, true, nil

	default:
		protocolNumber, err := strconv.Atoi(protocol)
		if err != nil {
			return nil, false, err
		}
		needsWildcard := protocolNumber != protocolTCP &&
			protocolNumber != protocolUDP &&
			protocolNumber != protocolSCTP

		return []int{protocolNumber}, needsWildcard, nil
	}
}

// expandalias has an input of either
// - a user
// - a group
// - a tag
// - a host
// - an ip
// - a cidr
// and transform these in IPAddresses.
func expandAlias(
	machines Machines,
	aclPolicy ACLPolicy,
	alias string,
) ([]string, error) {
	ips := []string{}
	if alias == "*" {
		return []string{"*"}, nil
	}

	log.Debug().
		Str("alias", alias).
		Msg("Expanding")

	if strings.HasPrefix(alias, "group:") {
		users, err := expandGroup(aclPolicy, alias)
		if err != nil {
			return ips, err
		}
		for _, n := range users {
			nodes := filterMachinesByUser(machines, n)
			for _, node := range nodes {
				ips = append(ips, node.IPAddresses.ToStringSlice()...)
			}
		}

		return ips, nil
	}

	if strings.HasPrefix(alias, "tag:") {
		// check for forced tags
		for _, machine := range machines {
			if contains(machine.ForcedTags, alias) {
				ips = append(ips, machine.IPAddresses.ToStringSlice()...)
			}
		}

		// find tag owners
		owners, err := expandTagOwners(aclPolicy, alias)
		if err != nil {
			if errors.Is(err, errInvalidTag) {
				if len(ips) == 0 {
					return ips, fmt.Errorf(
						"%w. %v isn't owned by a TagOwner and no forced tags are defined",
						errInvalidTag,
						alias,
					)
				}

				return ips, nil
			} else {
				return ips, err
			}
		}

		// filter out machines per tag owner
		for _, user := range owners {
			machines := filterMachinesByUser(machines, user)
			for _, machine := range machines {
				hi := machine.GetHostInfo()
				if contains(hi.RequestTags, alias) {
					ips = append(ips, machine.IPAddresses.ToStringSlice()...)
				}
			}
		}

		return ips, nil
	}

	// if alias is a user
	nodes := filterMachinesByUser(machines, alias)
	nodes = excludeCorrectlyTaggedNodes(aclPolicy, nodes, alias)

	for _, n := range nodes {
		ips = append(ips, n.IPAddresses.ToStringSlice()...)
	}
	if len(ips) > 0 {
		return ips, nil
	}

	// if alias is an host
	if h, ok := aclPolicy.Hosts[alias]; ok {
		log.Trace().Str("host", h.String()).Msg("expandAlias got hosts entry")

		return expandAlias(machines, aclPolicy, h.String())
	}

	// if alias is an IP
	if ip, err := netip.ParseAddr(alias); err == nil {
		log.Trace().Str("ip", ip.String()).Msg("expandAlias got ip")
		ips := []string{ip.String()}
		matches := machines.FilterByIP(ip)

		for _, machine := range matches {
			ips = append(ips, machine.IPAddresses.ToStringSlice()...)
		}

		return lo.Uniq(ips), nil
	}

	if cidr, err := netip.ParsePrefix(alias); err == nil {
		log.Trace().Str("cidr", cidr.String()).Msg("expandAlias got cidr")
		val := []string{cidr.String()}
		// This is suboptimal and quite expensive, but if we only add the cidr, we will miss all the relevant IPv6
		// addresses for the hosts that belong to tailscale. This doesnt really affect stuff like subnet routers.
		for _, machine := range machines {
			for _, ip := range machine.IPAddresses {
				// log.Trace().
				// 	Msgf("checking if machine ip (%s) is part of cidr (%s): %v, is single ip cidr (%v), addr: %s", ip.String(), cidr.String(), cidr.Contains(ip), cidr.IsSingleIP(), cidr.Addr().String())
				if cidr.Contains(ip) {
					val = append(val, machine.IPAddresses.ToStringSlice()...)
				}
			}
		}

		return lo.Uniq(val), nil
	}

	log.Warn().Msgf("No IPs found with the alias %v", alias)

	return ips, nil
}

// excludeCorrectlyTaggedNodes will remove from the list of input nodes the ones
// that are correctly tagged since they should not be listed as being in the user
// we assume in this function that we only have nodes from 1 user.
func excludeCorrectlyTaggedNodes(
	aclPolicy ACLPolicy,
	nodes []Machine,
	user string,
) []Machine {
	out := []Machine{}
	tags := []string{}
	for tag := range aclPolicy.TagOwners {
		owners, _ := expandTagOwners(aclPolicy, user)
		ns := append(owners, user)
		if contains(ns, user) {
			tags = append(tags, tag)
		}
	}
	// for each machine if tag is in tags list, don't append it.
	for _, machine := range nodes {
		hi := machine.GetHostInfo()

		found := false
		for _, t := range hi.RequestTags {
			if contains(tags, t) {
				found = true

				break
			}
		}
		if len(machine.ForcedTags) > 0 {
			found = true
		}
		if !found {
			out = append(out, machine)
		}
	}

	return out
}

func expandPorts(portsStr string, needsWildcard bool) (*[]tailcfg.PortRange, error) {
	if portsStr == "*" {
		return &[]tailcfg.PortRange{
			{First: portRangeBegin, Last: portRangeEnd},
		}, nil
	}

	if needsWildcard {
		return nil, errWildcardIsNeeded
	}

	ports := []tailcfg.PortRange{}
	for _, portStr := range strings.Split(portsStr, ",") {
		log.Trace().Msgf("parsing portstring: %s", portStr)
		rang := strings.Split(portStr, "-")
		switch len(rang) {
		case 1:
			port, err := strconv.ParseUint(rang[0], Base10, BitSize16)
			if err != nil {
				return nil, err
			}
			ports = append(ports, tailcfg.PortRange{
				First: uint16(port),
				Last:  uint16(port),
			})

		case expectedTokenItems:
			start, err := strconv.ParseUint(rang[0], Base10, BitSize16)
			if err != nil {
				return nil, err
			}
			last, err := strconv.ParseUint(rang[1], Base10, BitSize16)
			if err != nil {
				return nil, err
			}
			ports = append(ports, tailcfg.PortRange{
				First: uint16(start),
				Last:  uint16(last),
			})

		default:
			return nil, errInvalidPortFormat
		}
	}

	return &ports, nil
}

func filterMachinesByUser(machines []Machine, user string) []Machine {
	out := []Machine{}
	for _, machine := range machines {
		if machine.User.Name == user {
			out = append(out, machine)
		}
	}

	return out
}

// expandTagOwners will return a list of user. An owner can be either a user or a group
// a group cannot be composed of groups.
func expandTagOwners(aclPolicy ACLPolicy, tag string) ([]string, error) {
	var owners []string
	ows, ok := aclPolicy.TagOwners[tag]
	if !ok {
		return []string{}, fmt.Errorf(
			"%w. %v isn't owned by a TagOwner. Please add one first. https://tailscale.com/kb/1018/acls/#tag-owners",
			errInvalidTag,
			tag,
		)
	}
	for _, owner := range ows {
		if strings.HasPrefix(owner, "group:") {
			gs, err := expandGroup(aclPolicy, owner)
			if err != nil {
				return []string{}, err
			}
			owners = append(owners, gs...)
		} else {
			owners = append(owners, owner)
		}
	}

	return owners, nil
}

// expandGroup will return the list of user inside the group
// after some validation.
func expandGroup(aclPolicy ACLPolicy, group string) ([]string, error) {
	outGroups := []string{}
	aclGroups, ok := aclPolicy.Groups[group]
	if !ok {
		return []string{}, fmt.Errorf(
			"group %v isn't registered. %w",
			group,
			errInvalidGroup,
		)
	}
	for _, group := range aclGroups {
		if strings.HasPrefix(group, "group:") {
			return []string{}, fmt.Errorf(
				"%w. A group cannot be composed of groups. https://tailscale.com/kb/1018/acls/#groups",
				errInvalidGroup,
			)
		}
		grp, err := NormalizeToFQDNRules(group, false)
		if err != nil {
			return []string{}, fmt.Errorf(
				"failed to normalize group %q, err: %w",
				group,
				errInvalidGroup,
			)
		}
		outGroups = append(outGroups, grp)
	}

	return outGroups, nil
}