4 files changed, 63 insertions, 3 deletions
diff --git a/pkg/tcpip/network/ipv4/icmp.go b/pkg/tcpip/network/ipv4/icmp.go
index 83e71cb8c..94803a359 100644
--- a/pkg/tcpip/network/ipv4/icmp.go
+++ b/pkg/tcpip/network/ipv4/icmp.go
@@ -96,6 +96,26 @@ func (e *endpoint) handleICMP(r *stack.Route, pkt *stack.PacketBuffer) {
 			NetworkHeader: append(buffer.View(nil), pkt.NetworkHeader...),
 		})
 
+		remoteLinkAddr := r.RemoteLinkAddress
+
+		// As per RFC 1122 section 3.2.1.3, when a host sends any datagram, the IP
+		// source address MUST be one of its own IP addresses (but not a broadcast
+		// or multicast address).
+		localAddr := r.LocalAddress
+		if r.IsInboundBroadcast() || header.IsV4MulticastAddress(r.LocalAddress) {
+			localAddr = ""
+		}
+
+		r, err := r.Stack().FindRoute(e.NICID(), localAddr, r.RemoteAddress, ProtocolNumber, false /* multicastLoop */)
+		if err != nil {
+			// If we cannot find a route to the destination, silently drop the packet.
+			return
+		}
+		defer r.Release()
+
+		// Use the remote link address from the incoming packet.
+		r.ResolveWith(remoteLinkAddr)
+
 		vv := pkt.Data.Clone(nil)
 		vv.TrimFront(header.ICMPv4MinimumSize)
 		hdr := buffer.NewPrependable(int(r.MaxHeaderLength()) + header.ICMPv4MinimumSize)
diff --git a/pkg/tcpip/network/ipv6/icmp.go b/pkg/tcpip/network/ipv6/icmp.go
index 24600d877..ded91d83a 100644
--- a/pkg/tcpip/network/ipv6/icmp.go
+++ b/pkg/tcpip/network/ipv6/icmp.go
@@ -389,6 +389,26 @@ func (e *endpoint) handleICMP(r *stack.Route, pkt *stack.PacketBuffer, hasFragme
 			received.Invalid.Increment()
 			return
 		}
+
+		remoteLinkAddr := r.RemoteLinkAddress
+
+		// As per RFC 4291 section 2.7, multicast addresses must not be used as
+		// source addresses in IPv6 packets.
+		localAddr := r.LocalAddress
+		if header.IsV6MulticastAddress(r.LocalAddress) {
+			localAddr = ""
+		}
+
+		r, err := r.Stack().FindRoute(e.NICID(), localAddr, r.RemoteAddress, ProtocolNumber, false /* multicastLoop */)
+		if err != nil {
+			// If we cannot find a route to the destination, silently drop the packet.
+			return
+		}
+		defer r.Release()
+
+		// Use the link address from the source of the original packet.
+		r.ResolveWith(remoteLinkAddr)
+
 		pkt.Data.TrimFront(header.ICMPv6EchoMinimumSize)
 		hdr := buffer.NewPrependable(int(r.MaxHeaderLength()) + header.ICMPv6EchoMinimumSize)
 		packet := header.ICMPv6(hdr.Prepend(header.ICMPv6EchoMinimumSize))
diff --git a/pkg/tcpip/stack/route.go b/pkg/tcpip/stack/route.go
index 91e0110f1..9ce0a2c22 100644
--- a/pkg/tcpip/stack/route.go
+++ b/pkg/tcpip/stack/route.go
@@ -110,6 +110,12 @@ func (r *Route) GSOMaxSize() uint32 {
 	return 0
 }
 
+// ResolveWith immediately resolves a route with the specified remote link
+// address.
+func (r *Route) ResolveWith(addr tcpip.LinkAddress) {
+	r.RemoteLinkAddress = addr
+}
+
 // Resolve attempts to resolve the link address if necessary. Returns ErrWouldBlock in
 // case address resolution requires blocking, e.g. wait for ARP reply. Waker is
 // notified when address resolution is complete (success or not).
@@ -279,12 +285,26 @@ func (r *Route) Stack() *Stack {
 	return r.ref.stack()
 }
 
-// IsBroadcast returns true if the route is to send a broadcast packet.
-func (r *Route) IsBroadcast() bool {
+// IsOutboundBroadcast returns true if the route is for an outbound broadcast
+// packet.
+func (r *Route) IsOutboundBroadcast() bool {
 	// Only IPv4 has a notion of broadcast.
 	return r.directedBroadcast || r.RemoteAddress == header.IPv4Broadcast
 }
 
+// IsInboundBroadcast returns true if the route is for an inbound broadcast
+// packet.
+func (r *Route) IsInboundBroadcast() bool {
+	// Only IPv4 has a notion of broadcast.
+	if r.LocalAddress == header.IPv4Broadcast {
+		return true
+	}
+
+	addr := r.ref.addrWithPrefix()
+	subnet := addr.Subnet()
+	return subnet.IsBroadcast(r.LocalAddress)
+}
+
 // ReverseRoute returns new route with given source and destination address.
 func (r *Route) ReverseRoute(src tcpip.Address, dst tcpip.Address) Route {
 	return Route{
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index b7d735889..444b5b01c 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -499,7 +499,7 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 		resolve = route.Resolve
 	}
 
-	if !e.broadcast && route.IsBroadcast() {
+	if !e.broadcast && route.IsOutboundBroadcast() {
 		return 0, nil, tcpip.ErrBroadcastDisabled
 	}