route: treat short sockaddr lengths as unspecified

Previously, we enforced minimum length requirements for sockaddr, but
the route command can legitimately parse shorter lengths. This change
treats any sockaddr with length less than the address offset as an
unspecified address (0.0.0.0 for IPv4 or :: for IPv6), as discern by
monitoring the route command.

To replicate the issue, prior to the fix, execute the following:

First:
route -n monitor

Next:
sudo route -n add -inet6 -ifscope en11 -net :: \
    -netmask :: fe80::2d0:4cff:fe10:15d2

The route command that is actively monitoring will print something such
as:
RTM_ADD: Add Route: len 152, pid: 81198, seq 1, errno 0, ifscope 13, flags:<UP,GATEWAY,DONE,STATIC,IFSCOPE>
locks:  inits:
sockaddrs: <DST,GATEWAY,NETMASK>
:: fe80::2d0:4cff:fe10:15d2 ::

Prior to the fix, if you had attempted parse the above message, PareRIB
would have returned errInvalidAddr which is clearly false.

Fixes golang/go#71557

Change-Id: Iec86cc9b05a765b6e67e95a4e30ff31f66f3d17e
GitHub-Last-Rev: 396d8a2
GitHub-Pull-Request: #231
Reviewed-on: https://go-review.googlesource.com/c/net/+/646556
Commit-Queue: Ian Lance Taylor <iant@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

route/address.go

@@ -178,13 +178,13 @@ func parseInetAddr(af int, b []byte) (Addr, error) {
 	)
 	switch af {
 	case syscall.AF_INET:
-		if len(b) < (off4+1) || len(b) < int(b[0]) {
+		if len(b) < int(b[0]) {
 			return nil, errInvalidAddr
 		}
 		sockAddrLen := int(b[0])
 		a := &Inet4Addr{}
 		// sockAddrLen of 0 is valid and represents 0.0.0.0
-		if sockAddrLen != 0 {
+		if sockAddrLen > off4 {
 			// Calculate how many bytes of the address to copy:
 			// either full IPv4 length or the available length.
 			n := off4 + ipv4Len
@@ -195,13 +195,13 @@ func parseInetAddr(af int, b []byte) (Addr, error) {
 		}
 		return a, nil
 	case syscall.AF_INET6:
-		if len(b) < (off6+1) || len(b) < int(b[0]) {
+		if len(b) < int(b[0]) {
 			return nil, errInvalidAddr
 		}
 		sockAddrLen := int(b[0])
 		a := &Inet6Addr{}
 		// sockAddrLen of 0 is valid and represents ::
-		if sockAddrLen != 0 {
+		if sockAddrLen > off6 {
 			n := off6 + ipv6Len
 			if sockAddrLen < n {
 				n = sockAddrLen

route/address_darwin_test.go

@@ -96,6 +96,38 @@ var parseAddrsOnDarwinLittleEndianTests = []parseAddrsOnDarwinTest{
 			nil,
 		},
 	},
+	// sudo route -n add -inet6 -ifscope en11 -net :: -netmask :: fe80::2d0:4cff:fe10:15d2
+	// RTM_ADD: Add Route: len 152, pid: 81198, seq 1, errno 0, ifscope 13, flags:<UP,GATEWAY,DONE,STATIC,IFSCOPE>
+	// locks:  inits:
+	// sockaddrs: <DST,GATEWAY,NETMASK>
+	// :: fe80::2d0:4cff:fe10:15d2 ::
+	{
+		syscall.RTA_DST | syscall.RTA_GATEWAY | syscall.RTA_NETMASK,
+		parseKernelInetAddr,
+		[]byte{
+			0x1c, 0x1e, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x00, 0x00, 0x00, 0x00,
+
+			0x1c, 0x1e, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			0x02, 0xd0, 0x4c, 0xff, 0xfe, 0x10, 0x15, 0xd2,
+			0x00, 0x00, 0x00, 0x00,
+
+			0x02, 0x1e, 0x00, 0x00,
+		},
+		[]Addr{
+			&Inet6Addr{},
+			&Inet6Addr{IP: [16]byte{0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xd0, 0x4c, 0xff, 0xfe, 0x10, 0x15, 0xd2}},
+			&Inet6Addr{},
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+		},
+	},
 	// golang/go#70528, the kernel can produce addresses of length 0
 	{
 		syscall.RTA_DST | syscall.RTA_GATEWAY | syscall.RTA_NETMASK,