net: reject leading zeros in IP address parsers

In both net.ParseIP and net.ParseCIDR reject leading zeros in the
dot-decimal notation of IPv4 addresses.

Fixes #30999
Fixes #43389

Change-Id: I2b6a31fe84db89ac828cf5ed03eaa586ee96ab68
Reviewed-on: https://go-review.googlesource.com/c/go/+/325829
Trust: Roland Shoemaker <roland@golang.org>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

doc/go1.17.html

@@ -639,6 +639,16 @@ Do not send CLs removing the interior tags from such phrases.
       <a href="/pkg/net/#ParseError"><code>ParseError</code></a> error type now implement
       the <a href="/pkg/net/#Error"><code>net.Error</code></a> interface.
     </p>
+
+    <p><!-- CL325829 -->
+      The <a href="/pkg/net/#ParseIP"><code>ParseIP</code></a> and <a href="/pkg/net/#ParseCIDR"><code>ParseCIDR</code></a>
+      functions now reject IPv4 addresses which contain decimal components with leading zeros.
+
+      These components were always interpreted as decimal, but some operating systems treat them as octal.
+      This mismatch could hypothetically lead to security issues if a Go application was used to validate IP addresses
+      which were then used in their original form with non-Go applications which interpreted components as octal. Generally,
+      it is advisable to always re-encoded values after validation, which avoids this class of parser misalignment issues.
+    </p>
   </dd>
 </dl><!-- net -->
 

src/net/hosts_test.go

@@ -36,7 +36,7 @@ var lookupStaticHostTests = []struct {
 		},
 	},
 	{
-		"testdata/ipv4-hosts", // see golang.org/issue/8996
+		"testdata/ipv4-hosts",
 		[]staticHostEntry{
 			{"localhost", []string{"127.0.0.1", "127.0.0.2", "127.0.0.3"}},
 			{"localhost.localdomain", []string{"127.0.0.3"}},
@@ -102,7 +102,7 @@ var lookupStaticAddrTests = []struct {
 		},
 	},
 	{
-		"testdata/ipv4-hosts", // see golang.org/issue/8996
+		"testdata/ipv4-hosts",
 		[]staticHostEntry{
 			{"127.0.0.1", []string{"localhost"}},
 			{"127.0.0.2", []string{"localhost"}},

src/net/ip.go

@@ -574,6 +574,10 @@ func parseIPv4(s string) IP {
 		if !ok || n > 0xFF {
 			return nil
 		}
+		if c > 1 && s[0] == '0' {
+			// Reject non-zero components with leading zeroes.
+			return nil
+		}
 		s = s[c:]
 		p[i] = byte(n)
 	}

src/net/ip_test.go

@@ -21,9 +21,7 @@ var parseIPTests = []struct {
 }{
 	{"127.0.1.2", IPv4(127, 0, 1, 2)},
 	{"127.0.0.1", IPv4(127, 0, 0, 1)},
-	{"127.001.002.003", IPv4(127, 1, 2, 3)},
 	{"::ffff:127.1.2.3", IPv4(127, 1, 2, 3)},
-	{"::ffff:127.001.002.003", IPv4(127, 1, 2, 3)},
 	{"::ffff:7f01:0203", IPv4(127, 1, 2, 3)},
 	{"0:0:0:0:0000:ffff:127.1.2.3", IPv4(127, 1, 2, 3)},
 	{"0:0:0:0:000000:ffff:127.1.2.3", IPv4(127, 1, 2, 3)},
@@ -43,6 +41,11 @@ var parseIPTests = []struct {
 	{"fe80::1%911", nil},
 	{"", nil},
 	{"a1:a2:a3:a4::b1:b2:b3:b4", nil}, // Issue 6628
+	{"127.001.002.003", nil},
+	{"::ffff:127.001.002.003", nil},
+	{"123.000.000.000", nil},
+	{"1.2..4", nil},
+	{"0123.0.0.1", nil},
 }
 
 func TestParseIP(t *testing.T) {
@@ -358,6 +361,7 @@ var parseCIDRTests = []struct {
 	{"0.0.-2.0/32", nil, nil, &ParseError{Type: "CIDR address", Text: "0.0.-2.0/32"}},
 	{"0.0.0.-3/32", nil, nil, &ParseError{Type: "CIDR address", Text: "0.0.0.-3/32"}},
 	{"0.0.0.0/-0", nil, nil, &ParseError{Type: "CIDR address", Text: "0.0.0.0/-0"}},
+	{"127.000.000.001/32", nil, nil, &ParseError{Type: "CIDR address", Text: "127.000.000.001/32"}},
 	{"", nil, nil, &ParseError{Type: "CIDR address", Text: ""}},
 }
 

src/net/testdata/ipv4-hosts

@@ -1,12 +1,8 @@
 # See https://tools.ietf.org/html/rfc1123.
-#
-# The literal IPv4 address parser in the net package is a relaxed
-# one. It may accept a literal IPv4 address in dotted-decimal notation
-# with leading zeros such as "001.2.003.4".
 
 # internet address and host name
 127.0.0.1	localhost	# inline comment separated by tab
-127.000.000.002	localhost       # inline comment separated by space
+127.0.0.2	localhost   # inline comment separated by space
 
 # internet address, host name and aliases
-127.000.000.003	localhost	localhost.localdomain
+127.0.0.3	localhost	localhost.localdomain