net/http: do not send malformed cookie domain attribute

Malformed domain attributes are not sent in a Set-Cookie header.
Instead the domain attribute is dropped which turns the cookie
into a host-only cookie. This is much safer than dropping characters
from domain attribute.

Domain attributes with a leading dot '.' are still allowed, even
if discouraged by RFC 6265 section 4.1.1.

Fixes #6013

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/12745043

src/pkg/net/http/cookie.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"fmt"
 	"log"
+	"net"
 	"strconv"
 	"strings"
 	"time"
@@ -145,7 +146,15 @@ func (c *Cookie) String() string {
 		fmt.Fprintf(&b, "; Path=%s", sanitizeCookiePath(c.Path))
 	}
 	if len(c.Domain) > 0 {
-		fmt.Fprintf(&b, "; Domain=%s", sanitizeCookieDomain(c.Domain))
+		if validCookieDomain(c.Domain) {
+			// A c.Domain containing illegal characters is not
+			// sanitized but simply dropped which turns the cookie
+			// into a host-only cookie.
+			fmt.Fprintf(&b, "; Domain=%s", c.Domain)
+		} else {
+			log.Printf("net/http: invalid Cookie.Domain %q; dropping domain attribute",
+				c.Domain)
+		}
 	}
 	if c.Expires.Unix() > 0 {
 		fmt.Fprintf(&b, "; Expires=%s", c.Expires.UTC().Format(time.RFC1123))
@@ -208,26 +217,78 @@ func readCookies(h Header, filter string) []*Cookie {
 	return cookies
 }
 
-var cookieNameSanitizer = strings.NewReplacer("\n", "-", "\r", "-")
-
-// http://tools.ietf.org/html/rfc6265#section-4.1.1
-// domain-av         = "Domain=" domain-value
-// domain-value      = <subdomain>
-//	; defined in [RFC1034], Section 3.5, as
-//      ; enhanced by [RFC1123], Section 2.1
-func sanitizeCookieDomain(v string) string {
-	// TODO: implement http://tools.ietf.org/html/rfc1034#section-3.5
-	return oldCookieValueSanitizer.Replace(v)
+// validCookieDomain returns wheter v is a valid cookie domain-value.
+func validCookieDomain(v string) bool {
+	if isCookieDomainName(v) {
+		return true
+	}
+	if net.ParseIP(v) != nil && !strings.Contains(v, ":") {
+		return true
+	}
+	return false
 }
 
+// isCookieDomainName returns whether s is a valid domain name or a valid
+// domain name with a leading dot '.'.  It is almost a direct copy of
+// package net's isDomainName.
+func isCookieDomainName(s string) bool {
+	if len(s) == 0 {
+		return false
+	}
+	if len(s) > 255 {
+		return false
+	}
+
+	if s[0] == '.' {
+		// A cookie a domain attribute may start with a leading dot.
+		s = s[1:]
+	}
+	last := byte('.')
+	ok := false // Ok once we've seen a letter.
+	partlen := 0
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		switch {
+		default:
+			return false
+		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z':
+			// No '_' allowed here (in contrast to package net).
+			ok = true
+			partlen++
+		case '0' <= c && c <= '9':
+			// fine
+			partlen++
+		case c == '-':
+			// Byte before dash cannot be dot.
+			if last == '.' {
+				return false
+			}
+			partlen++
+		case c == '.':
+			// Byte before dot cannot be dot, dash.
+			if last == '.' || last == '-' {
+				return false
+			}
+			if partlen > 63 || partlen == 0 {
+				return false
+			}
+			partlen = 0
+		}
+		last = c
+	}
+	if last == '-' || partlen > 63 {
+		return false
+	}
+
+	return ok
+}
+
+var cookieNameSanitizer = strings.NewReplacer("\n", "-", "\r", "-")
+
 func sanitizeCookieName(n string) string {
 	return cookieNameSanitizer.Replace(n)
 }
 
-// This is the replacer used in the original Go cookie code.
-// It's not correct, but it's here for now until it's replaced.
-var oldCookieValueSanitizer = strings.NewReplacer("\n", " ", "\r", " ", ";", " ")
-
 // http://tools.ietf.org/html/rfc6265#section-4.1.1
 // cookie-value      = *cookie-octet / ( DQUOTE *cookie-octet DQUOTE )
 // cookie-octet      = %x21 / %x23-2B / %x2D-3A / %x3C-5B / %x5D-7E

src/pkg/net/http/cookie_test.go

@@ -32,6 +32,22 @@ var writeSetCookiesTests = []struct {
 		&Cookie{Name: "cookie-4", Value: "four", Path: "/restricted/"},
 		"cookie-4=four; Path=/restricted/",
 	},
+	{
+		&Cookie{Name: "cookie-5", Value: "five", Domain: "wrong;bad.abc"},
+		"cookie-5=five",
+	},
+	{
+		&Cookie{Name: "cookie-6", Value: "six", Domain: "bad-.abc"},
+		"cookie-6=six",
+	},
+	{
+		&Cookie{Name: "cookie-7", Value: "seven", Domain: "127.0.0.1"},
+		"cookie-7=seven; Domain=127.0.0.1",
+	},
+	{
+		&Cookie{Name: "cookie-8", Value: "eight", Domain: "::1"},
+		"cookie-8=eight",
+	},
 }
 
 func TestWriteSetCookies(t *testing.T) {