net/smtp: patch for SMTP injections

Fixes #21159.

Change-Id: I2c5ad505d673e213a548e5d632a5b3ad706e0dde
Reviewed-on: https://go-review.googlesource.com/67635
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/smtp/smtp.go

@@ -93,6 +93,9 @@ func (c *Client) hello() error {
 // automatically otherwise. If Hello is called, it must be called before
 // any of the other methods.
 func (c *Client) Hello(localName string) error {
+	if err := validateLine(localName); err != nil {
+		return err
+	}
 	if c.didHello {
 		return errors.New("smtp: Hello called after other methods")
 	}
@@ -179,6 +182,9 @@ func (c *Client) TLSConnectionState() (state tls.ConnectionState, ok bool) {
 // does not necessarily indicate an invalid address. Many servers
 // will not verify addresses for security reasons.
 func (c *Client) Verify(addr string) error {
+	if err := validateLine(addr); err != nil {
+		return err
+	}
 	if err := c.hello(); err != nil {
 		return err
 	}
@@ -237,6 +243,9 @@ func (c *Client) Auth(a Auth) error {
 // parameter.
 // This initiates a mail transaction and is followed by one or more Rcpt calls.
 func (c *Client) Mail(from string) error {
+	if err := validateLine(from); err != nil {
+		return err
+	}
 	if err := c.hello(); err != nil {
 		return err
 	}
@@ -254,6 +263,9 @@ func (c *Client) Mail(from string) error {
 // A call to Rcpt must be preceded by a call to Mail and may be followed by
 // a Data call or another Rcpt call.
 func (c *Client) Rcpt(to string) error {
+	if err := validateLine(to); err != nil {
+		return err
+	}
 	_, _, err := c.cmd(25, "RCPT TO:<%s>", to)
 	return err
 }
@@ -304,6 +316,14 @@ var testHookStartTLS func(*tls.Config) // nil, except for tests
 // functionality. Higher-level packages exist outside of the standard
 // library.
 func SendMail(addr string, a Auth, from string, to []string, msg []byte) error {
+	if err := validateLine(from); err != nil {
+		return err
+	}
+	for _, recp := range to {
+		if err := validateLine(recp); err != nil {
+			return err
+		}
+	}
 	c, err := Dial(addr)
 	if err != nil {
 		return err
@@ -388,3 +408,11 @@ func (c *Client) Quit() error {
 	}
 	return c.Text.Close()
 }
+
+// validateLine checks to see if a line has CR or LF as per RFC 5321
+func validateLine(line string) error {
+	if strings.ContainsAny(line, "\n\r") {
+		return errors.New("smtp: A line must not contain CR or LF")
+	}
+	return nil
+}

src/net/smtp/smtp_test.go

@@ -182,6 +182,9 @@ func TestBasic(t *testing.T) {
 	if err := c.Verify("user1@gmail.com"); err == nil {
 		t.Fatalf("First VRFY: expected no verification")
 	}
+	if err := c.Verify("user2@gmail.com>\r\nDATA\r\nAnother injected message body\r\n.\r\nQUIT\r\n"); err == nil {
+		t.Fatalf("VRFY should have failed due to a message injection attempt")
+	}
 	if err := c.Verify("user2@gmail.com"); err != nil {
 		t.Fatalf("Second VRFY: expected verification, got %s", err)
 	}
@@ -193,6 +196,12 @@ func TestBasic(t *testing.T) {
 		t.Fatalf("AUTH failed: %s", err)
 	}
 
+	if err := c.Rcpt("golang-nuts@googlegroups.com>\r\nDATA\r\nInjected message body\r\n.\r\nQUIT\r\n"); err == nil {
+		t.Fatalf("RCPT should have failed due to a message injection attempt")
+	}
+	if err := c.Mail("user@gmail.com>\r\nDATA\r\nAnother injected message body\r\n.\r\nQUIT\r\n"); err == nil {
+		t.Fatalf("MAIL should have failed due to a message injection attempt")
+	}
 	if err := c.Mail("user@gmail.com"); err != nil {
 		t.Fatalf("MAIL failed: %s", err)
 	}
@@ -375,6 +384,10 @@ func TestHello(t *testing.T) {
 
 		switch i {
 		case 0:
+			err = c.Hello("hostinjection>\n\rDATA\r\nInjected message body\r\n.\r\nQUIT\r\n")
+			if err == nil {
+				t.Errorf("Expected Hello to be rejected due to a message injection attempt")
+			}
 			err = c.Hello("customhost")
 		case 1:
 			err = c.StartTLS(nil)
@@ -506,6 +519,16 @@ func TestSendMail(t *testing.T) {
 		}
 	}(strings.Split(server, "\r\n"))
 
+	err = SendMail(l.Addr().String(), nil, "test@example.com", []string{"other@example.com>\n\rDATA\r\nInjected message body\r\n.\r\nQUIT\r\n"}, []byte(strings.Replace(`From: test@example.com
+To: other@example.com
+Subject: SendMail test
+
+SendMail is working for me.
+`, "\n", "\r\n", -1)))
+	if err == nil {
+		t.Errorf("Expected SendMail to be rejected due to a message injection attempt")
+	}
+
 	err = SendMail(l.Addr().String(), nil, "test@example.com", []string{"other@example.com"}, []byte(strings.Replace(`From: test@example.com
 To: other@example.com
 Subject: SendMail test