From a4dcc692011bf1ceca9b1a363fd83f3e59e399ee Mon Sep 17 00:00:00 2001
From: Adam Langley <agl@golang.org>
Date: Sun, 8 Nov 2015 19:10:14 -0800
Subject: [PATCH] crypto/tls: don't send IP literals as SNI values.
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https://tools.ietf.org/html/rfc6066#section-3 states:

  “Literal IPv4 and IPv6 addresses are not permitted in "HostName".”

However, if an IP literal was set as Config.ServerName (which could
happen as easily as calling Dial with an IP address) then the code would
send the IP literal as the SNI value.

This change filters out IP literals, as recognised by net.ParseIP, from
being sent as the SNI value.

Fixes #13111.

Change-Id: Ie9ec7acc767ae172b48c9c6dd8d84fa27b1cf0de
Reviewed-on: https://go-review.googlesource.com/16742
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>
---
 src/crypto/tls/common.go                |  3 ++-
 src/crypto/tls/handshake_client.go      |  9 ++++++++-
 src/crypto/tls/handshake_client_test.go | 27 +++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/src/crypto/tls/common.go b/src/crypto/tls/common.go
index d47dc6182f0d9..c68ebfe188b41 100644
--- a/src/crypto/tls/common.go
+++ b/src/crypto/tls/common.go
@@ -286,7 +286,8 @@ type Config struct {
 
 	// ServerName is used to verify the hostname on the returned
 	// certificates unless InsecureSkipVerify is given. It is also included
-	// in the client's handshake to support virtual hosting.
+	// in the client's handshake to support virtual hosting unless it is
+	// an IP address.
 	ServerName string
 
 	// ClientAuth determines the server's policy for
diff --git a/src/crypto/tls/handshake_client.go b/src/crypto/tls/handshake_client.go
index 0b591d7309c25..462acfd1a121a 100644
--- a/src/crypto/tls/handshake_client.go
+++ b/src/crypto/tls/handshake_client.go
@@ -49,13 +49,20 @@ func (c *Conn) clientHandshake() error {
 		return errors.New("tls: NextProtos values too large")
 	}
 
+	sni := c.config.ServerName
+	// IP address literals are not permitted as SNI values. See
+	// https://tools.ietf.org/html/rfc6066#section-3.
+	if net.ParseIP(sni) != nil {
+		sni = ""
+	}
+
 	hello := &clientHelloMsg{
 		vers:                c.config.maxVersion(),
 		compressionMethods:  []uint8{compressionNone},
 		random:              make([]byte, 32),
 		ocspStapling:        true,
 		scts:                true,
-		serverName:          c.config.ServerName,
+		serverName:          sni,
 		supportedCurves:     c.config.curvePreferences(),
 		supportedPoints:     []uint8{pointFormatUncompressed},
 		nextProtoNeg:        len(c.config.NextProtos) > 0,
diff --git a/src/crypto/tls/handshake_client_test.go b/src/crypto/tls/handshake_client_test.go
index 664fe8de6a0c7..b275da15d02ce 100644
--- a/src/crypto/tls/handshake_client_test.go
+++ b/src/crypto/tls/handshake_client_test.go
@@ -600,3 +600,30 @@ func TestHandshakClientSCTs(t *testing.T) {
 	}
 	runClientTestTLS12(t, test)
 }
+
+func TestNoIPAddressesInSNI(t *testing.T) {
+	for _, ipLiteral := range []string{"1.2.3.4", "::1"} {
+		c, s := net.Pipe()
+
+		go func() {
+			client := Client(c, &Config{ServerName: ipLiteral})
+			client.Handshake()
+		}()
+
+		var header [5]byte
+		if _, err := io.ReadFull(s, header[:]); err != nil {
+			t.Fatal(err)
+		}
+		recordLen := int(header[3])<<8 | int(header[4])
+
+		record := make([]byte, recordLen)
+		if _, err := io.ReadFull(s, record[:]); err != nil {
+			t.Fatal(err)
+		}
+		s.Close()
+
+		if bytes.Index(record, []byte(ipLiteral)) != -1 {
+			t.Errorf("IP literal %q found in ClientHello: %x", ipLiteral, record)
+		}
+	}
+}