Use 1 fragmentation component per IP stack

This will help manage memory consumption by IP reassembly when
receiving IP fragments on multiple network endpoints. Previously,
each endpoint would cap memory consumption at 4MB, but with this
change, each IP stack will cap memory consumption at 4MB.

No behaviour changes.

PiperOrigin-RevId: 324913904

pkg/tcpip/network/ipv4/ipv4.go

@@ -52,27 +52,25 @@ const (
 )
 
 type endpoint struct {
-	nicID         tcpip.NICID
-	id            stack.NetworkEndpointID
-	prefixLen     int
-	linkEP        stack.LinkEndpoint
-	dispatcher    stack.TransportDispatcher
-	fragmentation *fragmentation.Fragmentation
-	protocol      *protocol
-	stack         *stack.Stack
+	nicID      tcpip.NICID
+	id         stack.NetworkEndpointID
+	prefixLen  int
+	linkEP     stack.LinkEndpoint
+	dispatcher stack.TransportDispatcher
+	protocol   *protocol
+	stack      *stack.Stack
 }
 
 // NewEndpoint creates a new ipv4 endpoint.
 func (p *protocol) NewEndpoint(nicID tcpip.NICID, addrWithPrefix tcpip.AddressWithPrefix, linkAddrCache stack.LinkAddressCache, dispatcher stack.TransportDispatcher, linkEP stack.LinkEndpoint, st *stack.Stack) (stack.NetworkEndpoint, *tcpip.Error) {
 	e := &endpoint{
-		nicID:         nicID,
-		id:            stack.NetworkEndpointID{LocalAddress: addrWithPrefix.Address},
-		prefixLen:     addrWithPrefix.PrefixLen,
-		linkEP:        linkEP,
-		dispatcher:    dispatcher,
-		fragmentation: fragmentation.NewFragmentation(fragmentblockSize, fragmentation.HighFragThreshold, fragmentation.LowFragThreshold, fragmentation.DefaultReassembleTimeout),
-		protocol:      p,
-		stack:         st,
+		nicID:      nicID,
+		id:         stack.NetworkEndpointID{LocalAddress: addrWithPrefix.Address},
+		prefixLen:  addrWithPrefix.PrefixLen,
+		linkEP:     linkEP,
+		dispatcher: dispatcher,
+		protocol:   p,
+		stack:      st,
 	}
 
 	return e, nil
@@ -442,7 +440,9 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 		}
 		var ready bool
 		var err error
-		pkt.Data, ready, err = e.fragmentation.Process(
+		pkt.Data, ready, err = e.protocol.fragmentation.Process(
+			// As per RFC 791 section 2.3, the identification value is unique
+			// for a source-destination pair and protocol.
 			fragmentation.FragmentID{
 				Source:      h.SourceAddress(),
 				Destination: h.DestinationAddress(),
@@ -484,6 +484,8 @@ type protocol struct {
 	// uint8 portion of it is meaningful and it must be accessed
 	// atomically.
 	defaultTTL uint32
+
+	fragmentation *fragmentation.Fragmentation
 }
 
 // Number returns the ipv4 protocol number.
@@ -605,5 +607,10 @@ func NewProtocol() stack.NetworkProtocol {
 	}
 	hashIV := r[buckets]
 
-	return &protocol{ids: ids, hashIV: hashIV, defaultTTL: DefaultTTL}
+	return &protocol{
+		ids:           ids,
+		hashIV:        hashIV,
+		defaultTTL:    DefaultTTL,
+		fragmentation: fragmentation.NewFragmentation(fragmentblockSize, fragmentation.HighFragThreshold, fragmentation.LowFragThreshold, fragmentation.DefaultReassembleTimeout),
+	}
 }

pkg/tcpip/network/ipv6/ipv6.go

@@ -51,7 +51,6 @@ type endpoint struct {
 	linkEP        stack.LinkEndpoint
 	linkAddrCache stack.LinkAddressCache
 	dispatcher    stack.TransportDispatcher
-	fragmentation *fragmentation.Fragmentation
 	protocol      *protocol
 }
 
@@ -342,7 +341,7 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 			var ready bool
 			// Note that pkt doesn't have its transport header set after reassembly,
 			// and won't until DeliverNetworkPacket sets it.
-			pkt.Data, ready, err = e.fragmentation.Process(
+			pkt.Data, ready, err = e.protocol.fragmentation.Process(
 				// IPv6 ignores the Protocol field since the ID only needs to be unique
 				// across source-destination pairs, as per RFC 8200 section 4.5.
 				fragmentation.FragmentID{
@@ -445,7 +444,8 @@ type protocol struct {
 	// defaultTTL is the current default TTL for the protocol. Only the
 	// uint8 portion of it is meaningful and it must be accessed
 	// atomically.
-	defaultTTL uint32
+	defaultTTL    uint32
+	fragmentation *fragmentation.Fragmentation
 }
 
 // Number returns the ipv6 protocol number.
@@ -478,7 +478,6 @@ func (p *protocol) NewEndpoint(nicID tcpip.NICID, addrWithPrefix tcpip.AddressWi
 		linkEP:        linkEP,
 		linkAddrCache: linkAddrCache,
 		dispatcher:    dispatcher,
-		fragmentation: fragmentation.NewFragmentation(header.IPv6FragmentExtHdrFragmentOffsetBytesPerUnit, fragmentation.HighFragThreshold, fragmentation.LowFragThreshold, fragmentation.DefaultReassembleTimeout),
 		protocol:      p,
 	}, nil
 }
@@ -606,5 +605,8 @@ func calculateMTU(mtu uint32) uint32 {
 
 // NewProtocol returns an IPv6 network protocol.
 func NewProtocol() stack.NetworkProtocol {
-	return &protocol{defaultTTL: DefaultTTL}
+	return &protocol{
+		defaultTTL:    DefaultTTL,
+		fragmentation: fragmentation.NewFragmentation(header.IPv6FragmentExtHdrFragmentOffsetBytesPerUnit, fragmentation.HighFragThreshold, fragmentation.LowFragThreshold, fragmentation.DefaultReassembleTimeout),
+	}
 }