conn: store IP_PKTINFO cmsg in StdNetendpoint src

Replace the src storage inside StdNetEndpoint with a copy of the raw
control message buffer, to reduce allocation and perform less work on a
per-packet basis.

Signed-off-by: James Tucker <james@tailscale.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 56 insertions, 24 deletions

diff --git a/conn/sticky_linux_test.go b/conn/sticky_linux_test.go
index 0219ac3..679213a 100644
--- a/conn/sticky_linux_test.go
+++ b/conn/sticky_linux_test.go
@@ -18,13 +18,47 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+func setSrc(ep *StdNetEndpoint, addr netip.Addr, ifidx int32) {
+	var buf []byte
+	if addr.Is4() {
+		buf = make([]byte, unix.CmsgSpace(unix.SizeofInet4Pktinfo))
+		hdr := unix.Cmsghdr{
+			Level: unix.IPPROTO_IP,
+			Type:  unix.IP_PKTINFO,
+		}
+		hdr.SetLen(unix.CmsgLen(unix.SizeofInet4Pktinfo))
+		copy(buf, unsafe.Slice((*byte)(unsafe.Pointer(&hdr)), int(unsafe.Sizeof(hdr))))
+
+		info := unix.Inet4Pktinfo{
+			Ifindex:  ifidx,
+			Spec_dst: addr.As4(),
+		}
+		copy(buf[unix.CmsgLen(0):], unsafe.Slice((*byte)(unsafe.Pointer(&info)), unix.SizeofInet4Pktinfo))
+	} else {
+		buf = make([]byte, unix.CmsgSpace(unix.SizeofInet6Pktinfo))
+		hdr := unix.Cmsghdr{
+			Level: unix.IPPROTO_IPV6,
+			Type:  unix.IPV6_PKTINFO,
+		}
+		hdr.SetLen(unix.CmsgLen(unix.SizeofInet6Pktinfo))
+		copy(buf, unsafe.Slice((*byte)(unsafe.Pointer(&hdr)), int(unsafe.Sizeof(hdr))))
+
+		info := unix.Inet6Pktinfo{
+			Ifindex: uint32(ifidx),
+			Addr:    addr.As16(),
+		}
+		copy(buf[unix.CmsgLen(0):], unsafe.Slice((*byte)(unsafe.Pointer(&info)), unix.SizeofInet6Pktinfo))
+	}
+
+	ep.src = buf
+}
+
 func Test_setSrcControl(t *testing.T) {
 	t.Run("IPv4", func(t *testing.T) {
 		ep := &StdNetEndpoint{
 			AddrPort: netip.MustParseAddrPort("127.0.0.1:1234"),
 		}
-		ep.src.Addr = netip.MustParseAddr("127.0.0.1")
-		ep.src.ifidx = 5
+		setSrc(ep, netip.MustParseAddr("127.0.0.1"), 5)
 
 		control := make([]byte, srcControlSize)
 
@@ -53,8 +87,7 @@ func Test_setSrcControl(t *testing.T) {
 		ep := &StdNetEndpoint{
 			AddrPort: netip.MustParseAddrPort("[::1]:1234"),
 		}
-		ep.src.Addr = netip.MustParseAddr("::1")
-		ep.src.ifidx = 5
+		setSrc(ep, netip.MustParseAddr("::1"), 5)
 
 		control := make([]byte, srcControlSize)
 
@@ -80,7 +113,7 @@ func Test_setSrcControl(t *testing.T) {
 	})
 
 	t.Run("ClearOnNoSrc", func(t *testing.T) {
-		control := make([]byte, srcControlSize)
+		control := make([]byte, unix.CmsgLen(0))
 		hdr := (*unix.Cmsghdr)(unsafe.Pointer(&control[0]))
 		hdr.Level = 1
 		hdr.Type = 2
@@ -96,7 +129,7 @@ func Test_setSrcControl(t *testing.T) {
 
 func Test_getSrcFromControl(t *testing.T) {
 	t.Run("IPv4", func(t *testing.T) {
-		control := make([]byte, srcControlSize)
+		control := make([]byte, unix.CmsgSpace(unix.SizeofInet4Pktinfo))
 		hdr := (*unix.Cmsghdr)(unsafe.Pointer(&control[0]))
 		hdr.Level = unix.IPPROTO_IP
 		hdr.Type = unix.IP_PKTINFO
@@ -108,15 +141,15 @@ func Test_getSrcFromControl(t *testing.T) {
 		ep := &StdNetEndpoint{}
 		getSrcFromControl(control, ep)
 
-		if ep.src.Addr != netip.MustParseAddr("127.0.0.1") {
-			t.Errorf("unexpected address: %v", ep.src.Addr)
+		if ep.SrcIP() != netip.MustParseAddr("127.0.0.1") {
+			t.Errorf("unexpected address: %v", ep.SrcIP())
 		}
-		if ep.src.ifidx != 5 {
-			t.Errorf("unexpected ifindex: %d", ep.src.ifidx)
+		if ep.SrcIfidx() != 5 {
+			t.Errorf("unexpected ifindex: %d", ep.SrcIfidx())
 		}
 	})
 	t.Run("IPv6", func(t *testing.T) {
-		control := make([]byte, srcControlSize)
+		control := make([]byte, unix.CmsgSpace(unix.SizeofInet6Pktinfo))
 		hdr := (*unix.Cmsghdr)(unsafe.Pointer(&control[0]))
 		hdr.Level = unix.IPPROTO_IPV6
 		hdr.Type = unix.IPV6_PKTINFO
@@ -131,22 +164,21 @@ func Test_getSrcFromControl(t *testing.T) {
 		if ep.SrcIP() != netip.MustParseAddr("::1") {
 			t.Errorf("unexpected address: %v", ep.SrcIP())
 		}
-		if ep.src.ifidx != 5 {
-			t.Errorf("unexpected ifindex: %d", ep.src.ifidx)
+		if ep.SrcIfidx() != 5 {
+			t.Errorf("unexpected ifindex: %d", ep.SrcIfidx())
 		}
 	})
 	t.Run("ClearOnEmpty", func(t *testing.T) {
-		control := make([]byte, srcControlSize)
+		var control []byte
 		ep := &StdNetEndpoint{}
-		ep.src.Addr = netip.MustParseAddr("::1")
-		ep.src.ifidx = 5
+		setSrc(ep, netip.MustParseAddr("::1"), 5)
 
 		getSrcFromControl(control, ep)
 		if ep.SrcIP().IsValid() {
-			t.Errorf("unexpected address: %v", ep.src.Addr)
+			t.Errorf("unexpected address: %v", ep.SrcIP())
 		}
-		if ep.src.ifidx != 0 {
-			t.Errorf("unexpected ifindex: %d", ep.src.ifidx)
+		if ep.SrcIfidx() != 0 {
+			t.Errorf("unexpected ifindex: %d", ep.SrcIfidx())
 		}
 	})
 	t.Run("Multiple", func(t *testing.T) {
@@ -154,7 +186,7 @@ func Test_getSrcFromControl(t *testing.T) {
 		zeroHdr := (*unix.Cmsghdr)(unsafe.Pointer(&zeroControl[0]))
 		zeroHdr.SetLen(unix.CmsgLen(0))
 
-		control := make([]byte, srcControlSize)
+		control := make([]byte, unix.CmsgSpace(unix.SizeofInet4Pktinfo))
 		hdr := (*unix.Cmsghdr)(unsafe.Pointer(&control[0]))
 		hdr.Level = unix.IPPROTO_IP
 		hdr.Type = unix.IP_PKTINFO
@@ -170,11 +202,11 @@ func Test_getSrcFromControl(t *testing.T) {
 		ep := &StdNetEndpoint{}
 		getSrcFromControl(combined, ep)
 
-		if ep.src.Addr != netip.MustParseAddr("127.0.0.1") {
-			t.Errorf("unexpected address: %v", ep.src.Addr)
+		if ep.SrcIP() != netip.MustParseAddr("127.0.0.1") {
+			t.Errorf("unexpected address: %v", ep.SrcIP())
 		}
-		if ep.src.ifidx != 5 {
-			t.Errorf("unexpected ifindex: %d", ep.src.ifidx)
+		if ep.SrcIfidx() != 5 {
+			t.Errorf("unexpected ifindex: %d", ep.SrcIfidx())
 		}
 	})
 }