Only use the NextHeader value of the first IPv6 fragment extension header.

As per RFC 8200 Section 4.5:
  The Next Header field of the last header of the Per-Fragment
  headers is obtained from the Next Header field of the first
  fragment's Fragment header.

Test:
  - pkg/tcpip/network/ipv6:ipv6_test
  - pkg/tcpip/network/ipv4:ipv4_test
  - pkg/tcpip/network/fragmentation:fragmentation_test

Updates #2197

PiperOrigin-RevId: 327671635

1 files changed, 6 insertions, 4 deletions

diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index 0eafe9790..267d2cce8 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -321,10 +321,9 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 				return
 			}
 
-			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.protocol.fragmentation.Process(
+			data, proto, 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{
@@ -335,6 +334,7 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 				start,
 				last,
 				extHdr.More(),
+				uint8(rawPayload.Identifier),
 				rawPayload.Buf,
 			)
 			if err != nil {
@@ -342,12 +342,14 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 				r.Stats().IP.MalformedFragmentsReceived.Increment()
 				return
 			}
+			pkt.Data = data
 
 			if ready {
 				// We create a new iterator with the reassembled packet because we could
 				// have more extension headers in the reassembled payload, as per RFC
-				// 8200 section 4.5.
-				it = header.MakeIPv6PayloadIterator(rawPayload.Identifier, pkt.Data)
+				// 8200 section 4.5. We also use the NextHeader value from the first
+				// fragment.
+				it = header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(proto), pkt.Data)
 			}
 
 		case header.IPv6DestinationOptionsExtHdr: