error on undefined host in policy (#2490)

* add testcases

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* policy/v2: add validate to do post marshal validation

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

---------

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/policy/v2/filter_test.go

@@ -336,7 +336,7 @@ func TestParsing(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			pol, err := policyFromBytes([]byte(tt.acl))
+			pol, err := unmarshalPolicy([]byte(tt.acl))
 			if tt.wantErr && err == nil {
 				t.Errorf("parsing() error = %v, wantErr %v", err, tt.wantErr)
 

hscontrol/policy/v2/policy.go

@@ -42,7 +42,7 @@ type PolicyManager struct {
 // It returns an error if the policy file is invalid.
 // The policy manager will update the filter rules based on the users and nodes.
 func NewPolicyManager(b []byte, users []types.User, nodes types.Nodes) (*PolicyManager, error) {
-	policy, err := policyFromBytes(b)
+	policy, err := unmarshalPolicy(b)
 	if err != nil {
 		return nil, fmt.Errorf("parsing policy: %w", err)
 	}
@@ -137,7 +137,7 @@ func (pm *PolicyManager) SetPolicy(polB []byte) (bool, error) {
 		return false, nil
 	}
 
-	pol, err := policyFromBytes(polB)
+	pol, err := unmarshalPolicy(polB)
 	if err != nil {
 		return false, fmt.Errorf("parsing policy: %w", err)
 	}

hscontrol/policy/v2/types.go

@@ -532,7 +532,7 @@ Please check the format and try again.`, vs)
 type AliasEnc struct{ Alias }
 
 func (ve *AliasEnc) UnmarshalJSON(b []byte) error {
-	ptr, err := unmarshalPointer[Alias](
+	ptr, err := unmarshalPointer(
 		b,
 		parseAlias,
 	)
@@ -639,7 +639,7 @@ Please check the format and try again.`, s)
 type AutoApproverEnc struct{ AutoApprover }
 
 func (ve *AutoApproverEnc) UnmarshalJSON(b []byte) error {
-	ptr, err := unmarshalPointer[AutoApprover](
+	ptr, err := unmarshalPointer(
 		b,
 		parseAutoApprover,
 	)
@@ -659,7 +659,7 @@ type Owner interface {
 type OwnerEnc struct{ Owner }
 
 func (ve *OwnerEnc) UnmarshalJSON(b []byte) error {
-	ptr, err := unmarshalPointer[Owner](
+	ptr, err := unmarshalPointer(
 		b,
 		parseOwner,
 	)
@@ -769,6 +769,11 @@ func (h *Hosts) UnmarshalJSON(b []byte) error {
 	return nil
 }
 
+func (h Hosts) exist(name Host) bool {
+	_, ok := h[name]
+	return ok
+}
+
 // TagOwners are a map of Tag to a list of the UserEntities that own the tag.
 type TagOwners map[Tag]Owners
 
@@ -902,6 +907,39 @@ type Policy struct {
 	SSHs          []SSH              `json:"ssh"`
 }
 
+// validate reports if there are any errors in a policy after
+// the unmarshaling process.
+// It runs through all rules and checks if there are any inconsistencies
+// in the policy that needs to be addressed before it can be used.
+func (p *Policy) validate() error {
+	if p == nil {
+		panic("passed nil policy")
+	}
+
+	// All errors are collected and presented to the user,
+	// when adding more validation, please add to the list of errors.
+	var errs []error
+
+	for _, acl := range p.ACLs {
+		for _, src := range acl.Sources {
+			switch src.(type) {
+			case *Host:
+				h := src.(*Host)
+				if !p.Hosts.exist(*h) {
+					errs = append(errs, fmt.Errorf(`Host %q is not defined in the Policy, please define or remove the reference to it`, *h))
+				}
+			}
+		}
+	}
+
+	if len(errs) > 0 {
+		return multierr.New(errs...)
+	}
+
+	p.validated = true
+	return nil
+}
+
 // SSH controls who can ssh into which machines.
 type SSH struct {
 	Action       string        `json:"action"` // TODO(kradalby): add strict type
@@ -986,7 +1024,10 @@ func (u SSHUser) String() string {
 	return string(u)
 }
 
-func policyFromBytes(b []byte) (*Policy, error) {
+// unmarshalPolicy takes a byte slice and unmarshals it into a Policy struct.
+// In addition to unmarshalling, it will also validate the policy.
+// This is the only entrypoint of reading a policy from a file or other source.
+func unmarshalPolicy(b []byte) (*Policy, error) {
 	if b == nil || len(b) == 0 {
 		return nil, nil
 	}
@@ -1000,11 +1041,14 @@ func policyFromBytes(b []byte) (*Policy, error) {
 	ast.Standardize()
 	acl := ast.Pack()
 
-	err = json.Unmarshal(acl, &policy)
-	if err != nil {
+	if err = json.Unmarshal(acl, &policy); err != nil {
 		return nil, fmt.Errorf("parsing policy from bytes: %w", err)
 	}
 
+	if err := policy.validate(); err != nil {
+		return nil, err
+	}
+
 	return &policy, nil
 }
 

hscontrol/policy/v2/types_test.go

@@ -361,6 +361,65 @@ func TestUnmarshalPolicy(t *testing.T) {
 `,
 			wantErr: `AutoGroup is invalid, got: "autogroup:invalid", must be one of [autogroup:internet]`,
 		},
+		{
+			name: "undefined-hostname-errors-2490",
+			input: `
+{
+  "acls": [
+    {
+      "action": "accept",
+      "src": [
+        "user1"
+      ],
+      "dst": [
+        "user1:*"
+      ]
+    }
+  ]
+}
+`,
+			wantErr: `Host "user1" is not defined in the Policy, please define or remove the reference to it`,
+		},
+		{
+			name: "defined-hostname-does-not-err-2490",
+			input: `
+{
+  "hosts": {
+		"user1": "100.100.100.100",
+  },
+  "acls": [
+    {
+      "action": "accept",
+      "src": [
+        "user1"
+      ],
+      "dst": [
+        "user1:*"
+      ]
+    }
+  ]
+}
+`,
+			want: &Policy{
+				Hosts: Hosts{
+					"user1": Prefix(mp("100.100.100.100/32")),
+				},
+				ACLs: []ACL{
+					{
+						Action: "accept",
+						Sources: Aliases{
+							hp("user1"),
+						},
+						Destinations: []AliasWithPorts{
+							{
+								Alias: hp("user1"),
+								Ports: []tailcfg.PortRange{tailcfg.PortRangeAny},
+							},
+						},
+					},
+				},
+			},
+		},
 	}
 
 	cmps := append(util.Comparers, cmp.Comparer(func(x, y Prefix) bool {
@@ -370,7 +429,7 @@ func TestUnmarshalPolicy(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			policy, err := policyFromBytes([]byte(tt.input))
+			policy, err := unmarshalPolicy([]byte(tt.input))
 			if tt.wantErr == "" {
 				if err != nil {
 					t.Fatalf("got %v; want no error", err)