feat: add support for ssh acl policies

internal/domain/acl_ssh_policy.go

@@ -0,0 +1,150 @@
+package domain
+
+import (
+	"strings"
+	"tailscale.com/tailcfg"
+)
+
+func (a ACLPolicy) BuildSSHPolicy(srcs []Machine, dst *Machine) *tailcfg.SSHPolicy {
+	var rules []*tailcfg.SSHRule
+
+	expandSrcAliases := func(aliases []string, u *User) []*tailcfg.SSHPrincipal {
+		var allSrcIPsSet = &StringSet{}
+		for _, alias := range aliases {
+			for _, src := range srcs {
+				srcIPs := a.expandSSHSrcAlias(&src, alias, u)
+				allSrcIPsSet.Add(srcIPs...)
+			}
+		}
+
+		var result = []*tailcfg.SSHPrincipal{}
+		for _, i := range allSrcIPsSet.Items() {
+			result = append(result, &tailcfg.SSHPrincipal{NodeIP: i})
+		}
+
+		return result
+	}
+
+	for _, rule := range a.SSHRules {
+		if rule.Action != "accept" && rule.Action != "check" {
+			continue
+		}
+
+		var action = &tailcfg.SSHAction{
+			Accept:                   true,
+			AllowAgentForwarding:     true,
+			AllowLocalPortForwarding: true,
+		}
+
+		if rule.Action == "check" {
+			action = &tailcfg.SSHAction{
+				HoldAndDelegate: "https://unused/machine/ssh/action/$SRC_NODE_ID/to/$DST_NODE_ID",
+			}
+		}
+
+		selfUsers, otherUsers := a.expandSSHDstToSSHUsers(dst, rule)
+
+		if len(selfUsers) != 0 {
+			principals := expandSrcAliases(rule.Src, &dst.User)
+			if len(principals) != 0 {
+				rules = append(rules, &tailcfg.SSHRule{
+					Principals: principals,
+					SSHUsers:   selfUsers,
+					Action:     action,
+				})
+			}
+		}
+
+		if len(otherUsers) != 0 {
+			principals := expandSrcAliases(rule.Src, nil)
+			if len(principals) != 0 {
+				rules = append(rules, &tailcfg.SSHRule{
+					Principals: principals,
+					SSHUsers:   otherUsers,
+					Action:     action,
+				})
+			}
+		}
+	}
+
+	return &tailcfg.SSHPolicy{Rules: rules}
+}
+
+func (a ACLPolicy) expandSSHSrcAlias(m *Machine, alias string, dstUser *User) []string {
+	if dstUser != nil {
+		if !m.HasUser(dstUser.Name) || m.HasTags() {
+			return []string{}
+		}
+
+		if alias == AutoGroupMembers {
+			return m.IPs()
+		}
+
+		if strings.Contains(alias, "@") && m.HasUser(alias) {
+			return m.IPs()
+		}
+
+		if strings.HasPrefix(alias, "group:") && a.isGroupMember(alias, m) {
+			return m.IPs()
+		}
+
+		return []string{}
+	}
+
+	if alias == AutoGroupMembers && !m.HasTags() {
+		return m.IPs()
+	}
+
+	if strings.Contains(alias, "@") && !m.HasTags() && m.HasUser(alias) {
+		return m.IPs()
+	}
+
+	if strings.HasPrefix(alias, "group:") && !m.HasTags() && a.isGroupMember(alias, m) {
+		return m.IPs()
+	}
+
+	if strings.HasPrefix(alias, "tag:") && m.HasTag(alias) {
+		return m.IPs()
+	}
+
+	return []string{}
+}
+
+func (a ACLPolicy) expandSSHDstToSSHUsers(m *Machine, rule SSHRule) (map[string]string, map[string]string) {
+	users := buildSSHUsers(rule.Users)
+
+	var selfUsers map[string]string
+	var otherUsers map[string]string
+
+	for _, d := range rule.Dst {
+		if strings.HasPrefix(d, "tag:") && m.HasTag(d) {
+			otherUsers = users
+		}
+
+		if m.HasUser(d) || d == AutoGroupSelf {
+			selfUsers = users
+		}
+	}
+
+	return selfUsers, otherUsers
+}
+
+func buildSSHUsers(users []string) map[string]string {
+	var autogroupNonRoot = false
+	m := make(map[string]string)
+	for _, u := range users {
+		if u == "autogroup:nonroot" {
+			m["*"] = "="
+			autogroupNonRoot = true
+		} else {
+			m[u] = u
+		}
+	}
+
+	// disable root when autogroup:nonroot is used and root is not explicitly enabled
+	if _, exists := m["root"]; !exists && autogroupNonRoot {
+		m["root"] = ""
+	}
+
+	return m
+}