net/http: validate outgoing/client request trailers

This change validates outbound client request trailers
just like we do for headers. This helps prevent header
injection or other sorts of smuggling from easily being
performed using the standard HTTP client.

Fixes #64766

Change-Id: Idb34df876a0c308b1f57e9ae2695b118ac6bcc2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/572615
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
Auto-Submit: Emmanuel Odeke <emmanuel@orijtech.com>

src/net/http/transport.go

@@ -513,6 +513,22 @@ func (t *Transport) alternateRoundTripper(req *Request) RoundTripper {
 	return altProto[req.URL.Scheme]
 }
 
+func validateHeaders(hdrs Header) string {
+	for k, vv := range hdrs {
+		if !httpguts.ValidHeaderFieldName(k) {
+			return fmt.Sprintf("field name %q", k)
+		}
+		for _, v := range vv {
+			if !httpguts.ValidHeaderFieldValue(v) {
+				// Don't include the value in the error,
+				// because it may be sensitive.
+				return fmt.Sprintf("field value for %q", k)
+			}
+		}
+	}
+	return ""
+}
+
 // roundTrip implements a RoundTripper over HTTP.
 func (t *Transport) roundTrip(req *Request) (*Response, error) {
 	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
@@ -530,18 +546,16 @@ func (t *Transport) roundTrip(req *Request) (*Response, error) {
 	scheme := req.URL.Scheme
 	isHTTP := scheme == "http" || scheme == "https"
 	if isHTTP {
-		for k, vv := range req.Header {
-			if !httpguts.ValidHeaderFieldName(k) {
-				req.closeBody()
-				return nil, fmt.Errorf("net/http: invalid header field name %q", k)
-			}
-			for _, v := range vv {
-				if !httpguts.ValidHeaderFieldValue(v) {
-					req.closeBody()
-					// Don't include the value in the error, because it may be sensitive.
-					return nil, fmt.Errorf("net/http: invalid header field value for %q", k)
-				}
-			}
+		// Validate the outgoing headers.
+		if err := validateHeaders(req.Header); err != "" {
+			req.closeBody()
+			return nil, fmt.Errorf("net/http: invalid header %s", err)
+		}
+
+		// Validate the outgoing trailers too.
+		if err := validateHeaders(req.Trailer); err != "" {
+			req.closeBody()
+			return nil, fmt.Errorf("net/http: invalid trailer %s", err)
 		}
 	}
 

src/net/http/transport_test.go

@@ -7031,3 +7031,42 @@ func TestTransportReqCancelerCleanupOnRequestBodyWriteError(t *testing.T) {
 		return true
 	})
 }
+
+func TestValidateClientRequestTrailers(t *testing.T) {
+	run(t, testValidateClientRequestTrailers)
+}
+
+func testValidateClientRequestTrailers(t *testing.T, mode testMode) {
+	cst := newClientServerTest(t, mode, HandlerFunc(func(rw ResponseWriter, req *Request) {
+		rw.Write([]byte("Hello"))
+	})).ts
+
+	cases := []struct {
+		trailer Header
+		wantErr string
+	}{
+		{Header{"Trx": {"x\r\nX-Another-One"}}, `invalid trailer field value for "Trx"`},
+		{Header{"\r\nTrx": {"X-Another-One"}}, `invalid trailer field name "\r\nTrx"`},
+	}
+
+	for i, tt := range cases {
+		testName := fmt.Sprintf("%s%d", mode, i)
+		t.Run(testName, func(t *testing.T) {
+			req, err := NewRequest("GET", cst.URL, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			req.Trailer = tt.trailer
+			res, err := cst.Client().Do(req)
+			if err == nil {
+				t.Fatal("Expected an error")
+			}
+			if g, w := err.Error(), tt.wantErr; !strings.Contains(g, w) {
+				t.Fatalf("Mismatched error\n\t%q\ndoes not contain\n\t%q", g, w)
+			}
+			if res != nil {
+				t.Fatal("Unexpected non-nil response")
+			}
+		})
+	}
+}