[dockerfile2llb] fix daemon crash: check for circular dependency in convert

frontend/dockerfile/dockerfile2llb/convert.go

@@ -172,10 +172,6 @@ func Dockerfile2LLB(ctx context.Context, dt []byte, opt ConvertOpt) (*llb.State,
 		}
 	}
 
-	if len(allDispatchStates.states) == 1 {
-		allDispatchStates.states[0].stageName = ""
-	}
-
 	var target *dispatchState
 	if opt.Target == "" {
 		target = allDispatchStates.lastTarget()
@@ -207,6 +203,14 @@ func Dockerfile2LLB(ctx context.Context, dt []byte, opt ConvertOpt) (*llb.State,
 		}
 	}
 
+	if has, state := hasCircularDependency(allDispatchStates.states); has {
+		return nil, nil, fmt.Errorf("circular dependency detected on stage: %s", state.stageName)
+	}
+
+	if len(allDispatchStates.states) == 1 {
+		allDispatchStates.states[0].stageName = ""
+	}
+
 	eg, ctx := errgroup.WithContext(ctx)
 	for i, d := range allDispatchStates.states {
 		reachable := isReachable(target, d)
@@ -1130,6 +1134,41 @@ func isReachable(from, to *dispatchState) (ret bool) {
 	return false
 }
 
+func hasCircularDependency(states []*dispatchState) (bool, *dispatchState) {
+	var visit func(state *dispatchState) bool
+	if states == nil {
+		return false, nil
+	}
+	visited := make(map[*dispatchState]struct{})
+	path := make(map[*dispatchState]struct{})
+
+	visit = func(state *dispatchState) bool {
+		_, ok := visited[state]
+		if ok {
+			return false
+		}
+		visited[state] = struct{}{}
+		path[state] = struct{}{}
+		for dep := range state.deps {
+			_, ok = path[dep]
+			if ok {
+				return true
+			}
+			if visit(dep) {
+				return true
+			}
+		}
+		delete(path, state)
+		return false
+	}
+	for _, state := range states {
+		if visit(state) {
+			return true, state
+		}
+	}
+	return false, nil
+}
+
 func parseUser(str string) (uid uint32, gid uint32, err error) {
 	if str == "" {
 		return 0, 0, nil

frontend/dockerfile/dockerfile2llb/convert_test.go

@@ -152,3 +152,23 @@ func TestToEnvList(t *testing.T) {
 	resutl = toEnvMap(args, env)
 	assert.Equal(t, map[string]string{"key1": "val1", "key2": "v1"}, resutl)
 }
+
+func TestDockerfileCircularDependencies(t *testing.T) {
+	// single stage depends on itself
+	df := `FROM busybox AS stage0
+COPY --from=stage0 f1 /sub/
+`
+	_, _, err := Dockerfile2LLB(appcontext.Context(), []byte(df), ConvertOpt{})
+	assert.EqualError(t, err, "circular dependency detected on stage: stage0")
+
+	// multiple stages with circular dependency
+	df = `FROM busybox AS stage0
+COPY --from=stage2 f1 /sub/
+FROM busybox AS stage1
+COPY --from=stage0 f2 /sub/
+FROM busybox AS stage2
+COPY --from=stage1 f2 /sub/
+`
+	_, _, err = Dockerfile2LLB(appcontext.Context(), []byte(df), ConvertOpt{})
+	assert.EqualError(t, err, "circular dependency detected on stage: stage0")
+}