Make RedirectTarget thread safe

Fixes #4613.

PiperOrigin-RevId: 339746784

3 files changed, 28 insertions, 17 deletions

diff --git a/pkg/tcpip/stack/conntrack.go b/pkg/tcpip/stack/conntrack.go
index 0cd1da11f..4f4065f48 100644
--- a/pkg/tcpip/stack/conntrack.go
+++ b/pkg/tcpip/stack/conntrack.go
@@ -269,7 +269,7 @@ func (ct *ConnTrack) connForTID(tid tupleID) (*conn, direction) {
 	return nil, dirOriginal
 }
 
-func (ct *ConnTrack) insertRedirectConn(pkt *PacketBuffer, hook Hook, rt *RedirectTarget) *conn {
+func (ct *ConnTrack) insertRedirectConn(pkt *PacketBuffer, hook Hook, port uint16, address tcpip.Address) *conn {
 	tid, err := packetToTupleID(pkt)
 	if err != nil {
 		return nil
@@ -282,8 +282,8 @@ func (ct *ConnTrack) insertRedirectConn(pkt *PacketBuffer, hook Hook, rt *Redire
 	// rule. This tuple will be used to manipulate the packet in
 	// handlePacket.
 	replyTID := tid.reply()
-	replyTID.srcAddr = rt.Addr
-	replyTID.srcPort = rt.Port
+	replyTID.srcAddr = address
+	replyTID.srcPort = port
 	var manip manipType
 	switch hook {
 	case Prerouting:
diff --git a/pkg/tcpip/stack/iptables.go b/pkg/tcpip/stack/iptables.go
index df6bd1315..2d8c883cd 100644
--- a/pkg/tcpip/stack/iptables.go
+++ b/pkg/tcpip/stack/iptables.go
@@ -25,7 +25,7 @@ import (
 // TableID identifies a specific table.
 type TableID int
 
-// Each value identifies a specfic table.
+// Each value identifies a specific table.
 const (
 	NATID TableID = iota
 	MangleID
diff --git a/pkg/tcpip/stack/iptables_targets.go b/pkg/tcpip/stack/iptables_targets.go
index 94a5df329..ff55ef1a3 100644
--- a/pkg/tcpip/stack/iptables_targets.go
+++ b/pkg/tcpip/stack/iptables_targets.go
@@ -15,6 +15,8 @@
 package stack
 
 import (
+	"fmt"
+
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
@@ -81,25 +83,34 @@ func (*ReturnTarget) Action(*PacketBuffer, *ConnTrack, Hook, *GSO, *Route, tcpip
 	return RuleReturn, 0
 }
 
-// RedirectTarget redirects the packet by modifying the destination port/IP.
+// RedirectTarget redirects the packet to this machine by modifying the
+// destination port/IP. Outgoing packets are redirected to the loopback device,
+// and incoming packets are redirected to the incoming interface (rather than
+// forwarded).
+//
 // TODO(gvisor.dev/issue/170): Other flags need to be added after we support
 // them.
 type RedirectTarget struct {
-	// Addr indicates address used to redirect.
-	Addr tcpip.Address
-
-	// Port indicates port used to redirect.
+	// Port indicates port used to redirect. It is immutable.
 	Port uint16
 
-	// NetworkProtocol is the network protocol the target is used with.
+	// NetworkProtocol is the network protocol the target is used with. It
+	// is immutable.
 	NetworkProtocol tcpip.NetworkProtocolNumber
 }
 
 // Action implements Target.Action.
 // TODO(gvisor.dev/issue/170): Parse headers without copying. The current
-// implementation only works for PREROUTING and calls pkt.Clone(), neither
+// implementation only works for Prerouting and calls pkt.Clone(), neither
 // of which should be the case.
 func (rt *RedirectTarget) Action(pkt *PacketBuffer, ct *ConnTrack, hook Hook, gso *GSO, r *Route, address tcpip.Address) (RuleVerdict, int) {
+	// Sanity check.
+	if rt.NetworkProtocol != pkt.NetworkProtocolNumber {
+		panic(fmt.Sprintf(
+			"RedirectTarget.Action with NetworkProtocol %d called on packet with NetworkProtocolNumber %d",
+			rt.NetworkProtocol, pkt.NetworkProtocolNumber))
+	}
+
 	// Packet is already manipulated.
 	if pkt.NatDone {
 		return RuleAccept, 0
@@ -110,17 +121,17 @@ func (rt *RedirectTarget) Action(pkt *PacketBuffer, ct *ConnTrack, hook Hook, gs
 		return RuleDrop, 0
 	}
 
-	// Change the address to localhost (127.0.0.1 or ::1) in Output and to
+	// Change the address to loopback (127.0.0.1 or ::1) in Output and to
 	// the primary address of the incoming interface in Prerouting.
 	switch hook {
 	case Output:
 		if pkt.NetworkProtocolNumber == header.IPv4ProtocolNumber {
-			rt.Addr = tcpip.Address([]byte{127, 0, 0, 1})
+			address = tcpip.Address([]byte{127, 0, 0, 1})
 		} else {
-			rt.Addr = header.IPv6Loopback
+			address = header.IPv6Loopback
 		}
 	case Prerouting:
-		rt.Addr = address
+		// No-op, as address is already set correctly.
 	default:
 		panic("redirect target is supported only on output and prerouting hooks")
 	}
@@ -148,7 +159,7 @@ func (rt *RedirectTarget) Action(pkt *PacketBuffer, ct *ConnTrack, hook Hook, gs
 			}
 		}
 
-		pkt.Network().SetDestinationAddress(rt.Addr)
+		pkt.Network().SetDestinationAddress(address)
 
 		// After modification, IPv4 packets need a valid checksum.
 		if pkt.NetworkProtocolNumber == header.IPv4ProtocolNumber {
@@ -165,7 +176,7 @@ func (rt *RedirectTarget) Action(pkt *PacketBuffer, ct *ConnTrack, hook Hook, gs
 		// Set up conection for matching NAT rule. Only the first
 		// packet of the connection comes here. Other packets will be
 		// manipulated in connection tracking.
-		if conn := ct.insertRedirectConn(pkt, hook, rt); conn != nil {
+		if conn := ct.insertRedirectConn(pkt, hook, rt.Port, address); conn != nil {
 			ct.handlePacket(pkt, hook, gso, r)
 		}
 	default: