iptables - filter packets using outgoing interface.

Enables commands with -o (--out-interface) for iptables rules.
$ iptables -A OUTPUT -o eth0 -j ACCEPT

PiperOrigin-RevId: 310642286

4 files changed, 61 insertions, 12 deletions

diff --git a/pkg/tcpip/stack/iptables.go b/pkg/tcpip/stack/iptables.go
index 7c3c47d50..443423b3c 100644
--- a/pkg/tcpip/stack/iptables.go
+++ b/pkg/tcpip/stack/iptables.go
@@ -16,6 +16,7 @@ package stack
 
 import (
 	"fmt"
+	"strings"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
@@ -178,7 +179,7 @@ const (
 // dropped.
 //
 // Precondition: pkt.NetworkHeader is set.
-func (it *IPTables) Check(hook Hook, pkt *PacketBuffer, gso *GSO, r *Route, address tcpip.Address) bool {
+func (it *IPTables) Check(hook Hook, pkt *PacketBuffer, gso *GSO, r *Route, address tcpip.Address, nicName string) bool {
 	// Packets are manipulated only if connection and matching
 	// NAT rule exists.
 	it.connections.HandlePacket(pkt, hook, gso, r)
@@ -187,7 +188,7 @@ func (it *IPTables) Check(hook Hook, pkt *PacketBuffer, gso *GSO, r *Route, addr
 	for _, tablename := range it.Priorities[hook] {
 		table := it.Tables[tablename]
 		ruleIdx := table.BuiltinChains[hook]
-		switch verdict := it.checkChain(hook, pkt, table, ruleIdx, gso, r, address); verdict {
+		switch verdict := it.checkChain(hook, pkt, table, ruleIdx, gso, r, address, nicName); verdict {
 		// If the table returns Accept, move on to the next table.
 		case chainAccept:
 			continue
@@ -228,10 +229,10 @@ func (it *IPTables) Check(hook Hook, pkt *PacketBuffer, gso *GSO, r *Route, addr
 //
 // NOTE: unlike the Check API the returned map contains packets that should be
 // dropped.
-func (it *IPTables) CheckPackets(hook Hook, pkts PacketBufferList, gso *GSO, r *Route) (drop map[*PacketBuffer]struct{}, natPkts map[*PacketBuffer]struct{}) {
+func (it *IPTables) CheckPackets(hook Hook, pkts PacketBufferList, gso *GSO, r *Route, nicName string) (drop map[*PacketBuffer]struct{}, natPkts map[*PacketBuffer]struct{}) {
 	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
 		if !pkt.NatDone {
-			if ok := it.Check(hook, pkt, gso, r, ""); !ok {
+			if ok := it.Check(hook, pkt, gso, r, "", nicName); !ok {
 				if drop == nil {
 					drop = make(map[*PacketBuffer]struct{})
 				}
@@ -251,11 +252,11 @@ func (it *IPTables) CheckPackets(hook Hook, pkts PacketBufferList, gso *GSO, r *
 // Precondition: pkt is a IPv4 packet of at least length header.IPv4MinimumSize.
 // TODO(gvisor.dev/issue/170): pkt.NetworkHeader will always be set as a
 // precondition.
-func (it *IPTables) checkChain(hook Hook, pkt *PacketBuffer, table Table, ruleIdx int, gso *GSO, r *Route, address tcpip.Address) chainVerdict {
+func (it *IPTables) checkChain(hook Hook, pkt *PacketBuffer, table Table, ruleIdx int, gso *GSO, r *Route, address tcpip.Address, nicName string) chainVerdict {
 	// Start from ruleIdx and walk the list of rules until a rule gives us
 	// a verdict.
 	for ruleIdx < len(table.Rules) {
-		switch verdict, jumpTo := it.checkRule(hook, pkt, table, ruleIdx, gso, r, address); verdict {
+		switch verdict, jumpTo := it.checkRule(hook, pkt, table, ruleIdx, gso, r, address, nicName); verdict {
 		case RuleAccept:
 			return chainAccept
 
@@ -272,7 +273,7 @@ func (it *IPTables) checkChain(hook Hook, pkt *PacketBuffer, table Table, ruleId
 				ruleIdx++
 				continue
 			}
-			switch verdict := it.checkChain(hook, pkt, table, jumpTo, gso, r, address); verdict {
+			switch verdict := it.checkChain(hook, pkt, table, jumpTo, gso, r, address, nicName); verdict {
 			case chainAccept:
 				return chainAccept
 			case chainDrop:
@@ -298,7 +299,7 @@ func (it *IPTables) checkChain(hook Hook, pkt *PacketBuffer, table Table, ruleId
 // Precondition: pkt is a IPv4 packet of at least length header.IPv4MinimumSize.
 // TODO(gvisor.dev/issue/170): pkt.NetworkHeader will always be set as a
 // precondition.
-func (it *IPTables) checkRule(hook Hook, pkt *PacketBuffer, table Table, ruleIdx int, gso *GSO, r *Route, address tcpip.Address) (RuleVerdict, int) {
+func (it *IPTables) checkRule(hook Hook, pkt *PacketBuffer, table Table, ruleIdx int, gso *GSO, r *Route, address tcpip.Address, nicName string) (RuleVerdict, int) {
 	rule := table.Rules[ruleIdx]
 
 	// If pkt.NetworkHeader hasn't been set yet, it will be contained in
@@ -313,7 +314,7 @@ func (it *IPTables) checkRule(hook Hook, pkt *PacketBuffer, table Table, ruleIdx
 	}
 
 	// Check whether the packet matches the IP header filter.
-	if !filterMatch(rule.Filter, header.IPv4(pkt.NetworkHeader)) {
+	if !filterMatch(rule.Filter, header.IPv4(pkt.NetworkHeader), hook, nicName) {
 		// Continue on to the next rule.
 		return RuleJump, ruleIdx + 1
 	}
@@ -335,7 +336,7 @@ func (it *IPTables) checkRule(hook Hook, pkt *PacketBuffer, table Table, ruleIdx
 	return rule.Target.Action(pkt, &it.connections, hook, gso, r, address)
 }
 
-func filterMatch(filter IPHeaderFilter, hdr header.IPv4) bool {
+func filterMatch(filter IPHeaderFilter, hdr header.IPv4, hook Hook, nicName string) bool {
 	// TODO(gvisor.dev/issue/170): Support other fields of the filter.
 	// Check the transport protocol.
 	if filter.Protocol != 0 && filter.Protocol != hdr.TransportProtocol() {
@@ -355,5 +356,26 @@ func filterMatch(filter IPHeaderFilter, hdr header.IPv4) bool {
 		return false
 	}
 
+	// Check the output interface.
+	// TODO(gvisor.dev/issue/170): Add the check for FORWARD and POSTROUTING
+	// hooks after supported.
+	if hook == Output {
+		n := len(filter.OutputInterface)
+		if n == 0 {
+			return true
+		}
+
+		// If the interface name ends with '+', any interface which begins
+		// with the name should be matched.
+		ifName := filter.OutputInterface
+		matches = true
+		if strings.HasSuffix(ifName, "+") {
+			matches = strings.HasPrefix(nicName, ifName[:n-1])
+		} else {
+			matches = nicName == ifName
+		}
+		return filter.OutputInterfaceInvert != matches
+	}
+
 	return true
 }
diff --git a/pkg/tcpip/stack/iptables_types.go b/pkg/tcpip/stack/iptables_types.go
index 1bb0ba1bd..fe06007ae 100644
--- a/pkg/tcpip/stack/iptables_types.go
+++ b/pkg/tcpip/stack/iptables_types.go
@@ -158,6 +158,19 @@ type IPHeaderFilter struct {
 	// true the filter will match packets that fail the destination
 	// comparison.
 	DstInvert bool
+
+	// OutputInterface matches the name of the outgoing interface for the
+	// packet.
+	OutputInterface string
+
+	// OutputInterfaceMask masks the characters of the interface name when
+	// comparing with OutputInterface.
+	OutputInterfaceMask string
+
+	// OutputInterfaceInvert inverts the meaning of outgoing interface check,
+	// i.e. when true the filter will match packets that fail the outgoing
+	// interface comparison.
+	OutputInterfaceInvert bool
 }
 
 // A Matcher is the interface for matching packets.
diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index 8f4c1fe42..54103fdb3 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -1233,7 +1233,7 @@ func (n *NIC) DeliverNetworkPacket(linkEP LinkEndpoint, remote, local tcpip.Link
 		// iptables filtering.
 		ipt := n.stack.IPTables()
 		address := n.primaryAddress(protocol)
-		if ok := ipt.Check(Prerouting, &pkt, nil, nil, address.Address); !ok {
+		if ok := ipt.Check(Prerouting, &pkt, nil, nil, address.Address, ""); !ok {
 			// iptables is telling us to drop the packet.
 			return
 		}
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index e33fae4eb..b39ffa9fb 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -1898,9 +1898,23 @@ func (s *Stack) FindNetworkEndpoint(netProto tcpip.NetworkProtocolNumber, addres
 			nic.mu.RLock()
 			defer nic.mu.RUnlock()
 
-			// An endpoint with this id exists, check if it can be used and return it.
+			// An endpoint with this id exists, check if it can be
+			// used and return it.
 			return ref.ep, nil
 		}
 	}
 	return nil, tcpip.ErrBadAddress
 }
+
+// FindNICNameFromID returns the name of the nic for the given NICID.
+func (s *Stack) FindNICNameFromID(id tcpip.NICID) string {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	nic, ok := s.nics[id]
+	if !ok {
+		return ""
+	}
+
+	return nic.Name()
+}