syscall: fix alignment check for link-layer information on BSD variants

When link-layer information is wrapped with sockaddr_dl, we need to
follow the len field of sockaddr_dl. When link-layer information is
naked, we need to use the length of whole link-layer information.

Fixes #12641.

Change-Id: I4d377f64cbab1760b993fc55c719288616042bbb
Reviewed-on: https://go-review.googlesource.com/14939Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/route_bsd.go

@@ -44,6 +44,9 @@ func rsaAlignOf(salen int) int {
 
 // parseSockaddrLink parses b as a datalink socket address.
 func parseSockaddrLink(b []byte) (*SockaddrDatalink, error) {
+	if len(b) < 8 {
+		return nil, EINVAL
+	}
 	sa, _, err := parseLinkLayerAddr(b[4:])
 	if err != nil {
 		return nil, err
@@ -77,16 +80,16 @@ func parseLinkLayerAddr(b []byte) (*SockaddrDatalink, int, error) {
 		Slen byte
 	}
 	lla := (*linkLayerAddr)(unsafe.Pointer(&b[0]))
-	l := rsaAlignOf(int(4 + lla.Nlen + lla.Alen + lla.Slen))
+	l := 4 + int(lla.Nlen) + int(lla.Alen) + int(lla.Slen)
 	if len(b) < l {
 		return nil, 0, EINVAL
 	}
 	b = b[4:]
 	sa := &SockaddrDatalink{Type: lla.Type, Nlen: lla.Nlen, Alen: lla.Alen, Slen: lla.Slen}
-	for i := 0; len(sa.Data) > i && i < int(lla.Nlen+lla.Alen+lla.Slen); i++ {
+	for i := 0; len(sa.Data) > i && i < l-4; i++ {
 		sa.Data[i] = int8(b[i])
 	}
-	return sa, l, nil
+	return sa, rsaAlignOf(l), nil
 }
 
 // parseSockaddrInet parses b as an internet socket address.

src/syscall/route_bsd_test.go

@@ -119,6 +119,41 @@ func TestRouteMonitor(t *testing.T) {
 	<-tmo
 }
 
+var parseInterfaceMessageTests = []*syscall.InterfaceMessage{
+	// with link-layer address
+	{
+		Header: syscall.IfMsghdr{Version: syscall.RTM_VERSION, Addrs: syscall.RTA_IFP},
+		Data: []uint8{
+			0x11, 0x12, 0x2, 0x0, 0x6, 0x3, 0x6, 0x0,
+			0x77, 0x6d, 0x31, 0x01, 0x23, 0x45, 0xab, 0xcd,
+			0xef, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
+		},
+	},
+	// without link-layer address
+	{
+		Header: syscall.IfMsghdr{Version: syscall.RTM_VERSION, Addrs: syscall.RTA_IFP},
+		Data: []uint8{
+			0xe, 0x12, 0x4, 0x0, 0xf5, 0x6, 0x0, 0x0,
+			0x70, 0x66, 0x6c, 0x6f, 0x67, 0x30, 0x0, 0x0,
+		},
+	},
+	// no data
+	{
+		Header: syscall.IfMsghdr{Version: syscall.RTM_VERSION, Addrs: syscall.RTA_IFP},
+		Data: []uint8{
+			0x8, 0xa, 0xb, 0xc, 0xd, 0x0, 0x0, 0x0,
+		},
+	},
+}
+
+func TestParseInterfaceMessage(t *testing.T) {
+	for i, tt := range parseInterfaceMessageTests {
+		if _, err := syscall.ParseRoutingSockaddr(tt); err != nil {
+			t.Errorf("#%d: %v", i, err)
+		}
+	}
+}
+
 type addrFamily byte
 
 func (f addrFamily) String() string {