Preserve all unknown PolicyRequirement fields on (podman image trust set)

We are unmarshaling and re-marshaling JSON, which can _silently_ drop data
with the Go design decision.data.

Try harder, by using json.RawMessage at least for the data we care about.

Alternatively, this could use json.Decoder.DisallowUnknownFields.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

pkg/trust/policy.go

@@ -40,6 +40,18 @@ type repoContent struct {
 	SignedIdentity json.RawMessage `json:"signedIdentity,omitempty"`
 }
 
+// genericPolicyContent is the overall structure of a policy.json file (= c/image/v5/signature.Policy), using generic data for individual requirements.
+type genericPolicyContent struct {
+	Default    json.RawMessage          `json:"default"`
+	Transports genericTransportsContent `json:"transports,omitempty"`
+}
+
+// genericTransportsContent contains policies for individual transports (= c/image/v5/signature.Policy.Transports), using generic data for individual requirements.
+type genericTransportsContent map[string]genericRepoMap
+
+// genericRepoMap maps a scope name to requirements that apply to that scope (= c/image/v5/signature.PolicyTransportScopes)
+type genericRepoMap map[string]json.RawMessage
+
 // DefaultPolicyPath returns a path to the default policy of the system.
 func DefaultPolicyPath(sys *types.SystemContext) string {
 	systemDefaultPolicyPath := "/etc/containers/policy.json"
@@ -152,7 +164,7 @@ type AddPolicyEntriesInput struct {
 // AddPolicyEntries adds one or more policy entries necessary to implement AddPolicyEntriesInput.
 func AddPolicyEntries(policyPath string, input AddPolicyEntriesInput) error {
 	var (
-		policyContentStruct policyContent
+		policyContentStruct genericPolicyContent
 		newReposContent     []repoContent
 	)
 	trustType := input.Type
@@ -188,8 +200,12 @@ func AddPolicyEntries(policyPath string, input AddPolicyEntriesInput) error {
 	default:
 		return fmt.Errorf("unknown trust type %q", input.Type)
 	}
+	newReposJSON, err := json.Marshal(newReposContent)
+	if err != nil {
+		return err
+	}
 
-	_, err := os.Stat(policyPath)
+	_, err = os.Stat(policyPath)
 	if !os.IsNotExist(err) {
 		policyContent, err := ioutil.ReadFile(policyPath)
 		if err != nil {
@@ -200,7 +216,7 @@ func AddPolicyEntries(policyPath string, input AddPolicyEntriesInput) error {
 		}
 	}
 	if input.Scope == "default" {
-		policyContentStruct.Default = newReposContent
+		policyContentStruct.Default = json.RawMessage(newReposJSON)
 	} else {
 		if len(policyContentStruct.Default) == 0 {
 			return errors.New("default trust policy must be set")
@@ -209,18 +225,18 @@ func AddPolicyEntries(policyPath string, input AddPolicyEntriesInput) error {
 		for transport, transportval := range policyContentStruct.Transports {
 			_, registryExists = transportval[input.Scope]
 			if registryExists {
-				policyContentStruct.Transports[transport][input.Scope] = newReposContent
+				policyContentStruct.Transports[transport][input.Scope] = json.RawMessage(newReposJSON)
 				break
 			}
 		}
 		if !registryExists {
 			if policyContentStruct.Transports == nil {
-				policyContentStruct.Transports = make(map[string]repoMap)
+				policyContentStruct.Transports = make(map[string]genericRepoMap)
 			}
 			if policyContentStruct.Transports["docker"] == nil {
-				policyContentStruct.Transports["docker"] = make(map[string][]repoContent)
+				policyContentStruct.Transports["docker"] = make(map[string]json.RawMessage)
 			}
-			policyContentStruct.Transports["docker"][input.Scope] = append(policyContentStruct.Transports["docker"][input.Scope], newReposContent...)
+			policyContentStruct.Transports["docker"][input.Scope] = json.RawMessage(newReposJSON)
 		}
 	}
 

pkg/trust/policy_test.go

@@ -108,6 +108,70 @@ func TestAddPolicyEntries(t *testing.T) {
 			},
 		},
 	}, parsedPolicy)
+
+	// Test that completely unknown JSON is preserved
+	jsonWithUnknownData := `{
+    "default": [
+        {
+            "type": "this is unknown",
+			"unknown field": "should be preserved"
+        }
+    ],
+    "transports":
+        {
+            "docker-daemon":
+                {
+                    "": [{
+						"type":"this is unknown 2",
+						"unknown field 2": "should be preserved 2"
+						}]
+                }
+        }
+}`
+	err = os.WriteFile(policyPath, []byte(jsonWithUnknownData), 0600)
+	require.NoError(t, err)
+	err = AddPolicyEntries(policyPath, AddPolicyEntriesInput{
+		Scope:       "quay.io/innocuous",
+		Type:        "signedBy",
+		PubKeyFiles: []string{"/1.pub"},
+	})
+	require.NoError(t, err)
+	updatedJSONWithUnknownData, err := os.ReadFile(policyPath)
+	require.NoError(t, err)
+	// Decode updatedJSONWithUnknownData so that this test does not depend on details of the encoding.
+	// To reduce noise in the constants below:
+	type a = []interface{}
+	type m = map[string]interface{}
+	var parsedUpdatedJSON m
+	err = json.Unmarshal(updatedJSONWithUnknownData, &parsedUpdatedJSON)
+	require.NoError(t, err)
+	assert.Equal(t, m{
+		"default": a{
+			m{
+				"type":          "this is unknown",
+				"unknown field": "should be preserved",
+			},
+		},
+		"transports": m{
+			"docker-daemon": m{
+				"": a{
+					m{
+						"type":            "this is unknown 2",
+						"unknown field 2": "should be preserved 2",
+					},
+				},
+			},
+			"docker": m{
+				"quay.io/innocuous": a{
+					m{
+						"type":    "signedBy",
+						"keyType": "GPGKeys",
+						"keyPath": "/1.pub",
+					},
+				},
+			},
+		},
+	}, parsedUpdatedJSON)
 }
 
 // xNewPRSignedByKeyPath is a wrapper for NewPRSignedByKeyPath which must not fail.