Update the TTL field in forwarded packets

Closes: #1085

3 files changed, 41 insertions, 0 deletions

diff --git a/pkg/tcpip/network/arp/arp.go b/pkg/tcpip/network/arp/arp.go
index e9fcc89a8..9ffacd544 100644
--- a/pkg/tcpip/network/arp/arp.go
+++ b/pkg/tcpip/network/arp/arp.go
@@ -124,6 +124,10 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt tcpip.PacketBuffer) {
 	}
 }
 
+func (*endpoint) UpdateTTL(tcpip.PacketBuffer, uint8) *tcpip.Error {
+	return tcpip.ErrNotSupported
+}
+
 // protocol implements stack.NetworkProtocol and stack.LinkAddressResolver.
 type protocol struct {
 }
diff --git a/pkg/tcpip/network/ipv4/ipv4.go b/pkg/tcpip/network/ipv4/ipv4.go
index 4f1742938..9953f83cd 100644
--- a/pkg/tcpip/network/ipv4/ipv4.go
+++ b/pkg/tcpip/network/ipv4/ipv4.go
@@ -21,6 +21,7 @@
 package ipv4
 
 import (
+	"fmt"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -407,6 +408,24 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt tcpip.PacketBuffer) {
 	e.dispatcher.DeliverTransportPacket(r, p, pkt)
 }
 
+func (*endpoint) UpdateTTL(pkt tcpip.PacketBuffer, n uint8) *tcpip.Error {
+	headerView := pkt.Header.View()
+	h := header.IPv4(headerView)
+	if !h.IsValid(pkt.Data.Size()) {
+		fmt.Println("Malformed packet", len(h), int(h.HeaderLength()), int(h.TotalLength()), header.IPVersion(h), pkt.Data.Size())
+		//r.Stats().IP.MalformedPacketsReceived.Increment()
+		return tcpip.ErrInvalidOptionValue
+	}
+	//pkt.NetworkHeader = headerView[:h.HeaderLength()]
+
+	ttl := h.TTL()
+	if ttl <= n {
+		return tcpip.ErrTimeout
+	}
+	h.UpdateTTL(n)
+	return nil
+}
+
 // Close cleans up resources associated with the endpoint.
 func (e *endpoint) Close() {}
 
diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index 9aef5234b..df86dd3b2 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -21,6 +21,7 @@
 package ipv6
 
 import (
+	"fmt"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -189,6 +190,23 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt tcpip.PacketBuffer) {
 	e.dispatcher.DeliverTransportPacket(r, p, pkt)
 }
 
+func (*endpoint) UpdateTTL(pkt tcpip.PacketBuffer, n uint8) *tcpip.Error {
+	headerView := pkt.Header.View()
+	h := header.IPv6(headerView)
+	if !h.IsValid(pkt.Data.Size()) {
+		fmt.Println("Malformed packet", len(h), header.IPVersion(h), pkt.Data.Size())
+		//r.Stats().IP.MalformedPacketsReceived.Increment()
+		return tcpip.ErrInvalidOptionValue
+	}
+
+	ttl := h.HopLimit()
+	if ttl <= n {
+		return tcpip.ErrTimeout
+	}
+	h.SetHopLimit(ttl - n)
+	return nil
+}
+
 // Close cleans up resources associated with the endpoint.
 func (*endpoint) Close() {}