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

4 files changed, 75 insertions, 34 deletions

diff --git a/pkg/tcpip/network/fragmentation/BUILD b/pkg/tcpip/network/fragmentation/BUILD
index d1c728ccf..96c5f42f8 100644
--- a/pkg/tcpip/network/fragmentation/BUILD
+++ b/pkg/tcpip/network/fragmentation/BUILD
@@ -41,5 +41,7 @@ go_test(
         "reassembler_test.go",
     ],
     library = ":fragmentation",
-    deps = ["//pkg/tcpip/buffer"],
+    deps = [
+        "//pkg/tcpip/buffer",
+    ],
 )
diff --git a/pkg/tcpip/network/fragmentation/fragmentation.go b/pkg/tcpip/network/fragmentation/fragmentation.go
index 1827666c5..6a4843f92 100644
--- a/pkg/tcpip/network/fragmentation/fragmentation.go
+++ b/pkg/tcpip/network/fragmentation/fragmentation.go
@@ -120,29 +120,36 @@ func NewFragmentation(blockSize uint16, highMemoryLimit, lowMemoryLimit int, rea
 }
 
 // Process processes an incoming fragment belonging to an ID and returns a
-// complete packet when all the packets belonging to that ID have been received.
+// complete packet and its protocol number when all the packets belonging to
+// that ID have been received.
 //
 // [first, last] is the range of the fragment bytes.
 //
 // first must be a multiple of the block size f is configured with. The size
 // of the fragment data must be a multiple of the block size, unless there are
 // no fragments following this fragment (more set to false).
-func (f *Fragmentation) Process(id FragmentID, first, last uint16, more bool, vv buffer.VectorisedView) (buffer.VectorisedView, bool, error) {
+//
+// proto is the protocol number marked in the fragment being processed. It has
+// to be given here outside of the FragmentID struct because IPv6 should not use
+// the protocol to identify a fragment.
+func (f *Fragmentation) Process(
+	id FragmentID, first, last uint16, more bool, proto uint8, vv buffer.VectorisedView) (
+	buffer.VectorisedView, uint8, bool, error) {
 	if first > last {
-		return buffer.VectorisedView{}, false, fmt.Errorf("first=%d is greater than last=%d: %w", first, last, ErrInvalidArgs)
+		return buffer.VectorisedView{}, 0, false, fmt.Errorf("first=%d is greater than last=%d: %w", first, last, ErrInvalidArgs)
 	}
 
 	if first%f.blockSize != 0 {
-		return buffer.VectorisedView{}, false, fmt.Errorf("first=%d is not a multiple of block size=%d: %w", first, f.blockSize, ErrInvalidArgs)
+		return buffer.VectorisedView{}, 0, false, fmt.Errorf("first=%d is not a multiple of block size=%d: %w", first, f.blockSize, ErrInvalidArgs)
 	}
 
 	fragmentSize := last - first + 1
 	if more && fragmentSize%f.blockSize != 0 {
-		return buffer.VectorisedView{}, false, fmt.Errorf("fragment size=%d bytes is not a multiple of block size=%d on non-final fragment: %w", fragmentSize, f.blockSize, ErrInvalidArgs)
+		return buffer.VectorisedView{}, 0, false, fmt.Errorf("fragment size=%d bytes is not a multiple of block size=%d on non-final fragment: %w", fragmentSize, f.blockSize, ErrInvalidArgs)
 	}
 
 	if l := vv.Size(); l < int(fragmentSize) {
-		return buffer.VectorisedView{}, false, fmt.Errorf("got fragment size=%d bytes less than the expected fragment size=%d bytes (first=%d last=%d): %w", l, fragmentSize, first, last, ErrInvalidArgs)
+		return buffer.VectorisedView{}, 0, false, fmt.Errorf("got fragment size=%d bytes less than the expected fragment size=%d bytes (first=%d last=%d): %w", l, fragmentSize, first, last, ErrInvalidArgs)
 	}
 	vv.CapLength(int(fragmentSize))
 
@@ -160,14 +167,14 @@ func (f *Fragmentation) Process(id FragmentID, first, last uint16, more bool, vv
 	}
 	f.mu.Unlock()
 
-	res, done, consumed, err := r.process(first, last, more, vv)
+	res, firstFragmentProto, done, consumed, err := r.process(first, last, more, proto, vv)
 	if err != nil {
 		// We probably got an invalid sequence of fragments. Just
 		// discard the reassembler and move on.
 		f.mu.Lock()
 		f.release(r)
 		f.mu.Unlock()
-		return buffer.VectorisedView{}, false, fmt.Errorf("fragmentation processing error: %v", err)
+		return buffer.VectorisedView{}, 0, false, fmt.Errorf("fragmentation processing error: %w", err)
 	}
 	f.mu.Lock()
 	f.size += consumed
@@ -186,7 +193,7 @@ func (f *Fragmentation) Process(id FragmentID, first, last uint16, more bool, vv
 		}
 	}
 	f.mu.Unlock()
-	return res, done, nil
+	return res, firstFragmentProto, done, nil
 }
 
 func (f *Fragmentation) release(r *reassembler) {
diff --git a/pkg/tcpip/network/fragmentation/fragmentation_test.go b/pkg/tcpip/network/fragmentation/fragmentation_test.go
index 9eedd33c4..416604659 100644
--- a/pkg/tcpip/network/fragmentation/fragmentation_test.go
+++ b/pkg/tcpip/network/fragmentation/fragmentation_test.go
@@ -38,12 +38,14 @@ type processInput struct {
 	first uint16
 	last  uint16
 	more  bool
+	proto uint8
 	vv    buffer.VectorisedView
 }
 
 type processOutput struct {
-	vv   buffer.VectorisedView
-	done bool
+	vv    buffer.VectorisedView
+	proto uint8
+	done  bool
 }
 
 var processTestCases = []struct {
@@ -63,6 +65,17 @@ var processTestCases = []struct {
 		},
 	},
 	{
+		comment: "Next Header protocol mismatch",
+		in: []processInput{
+			{id: FragmentID{ID: 0}, first: 0, last: 1, more: true, proto: 6, vv: vv(2, "01")},
+			{id: FragmentID{ID: 0}, first: 2, last: 3, more: false, proto: 17, vv: vv(2, "23")},
+		},
+		out: []processOutput{
+			{vv: buffer.VectorisedView{}, done: false},
+			{vv: vv(4, "01", "23"), proto: 6, done: true},
+		},
+	},
+	{
 		comment: "Two IDs",
 		in: []processInput{
 			{id: FragmentID{ID: 0}, first: 0, last: 1, more: true, vv: vv(2, "01")},
@@ -83,18 +96,26 @@ func TestFragmentationProcess(t *testing.T) {
 	for _, c := range processTestCases {
 		t.Run(c.comment, func(t *testing.T) {
 			f := NewFragmentation(minBlockSize, 1024, 512, DefaultReassembleTimeout)
+			firstFragmentProto := c.in[0].proto
 			for i, in := range c.in {
-				vv, done, err := f.Process(in.id, in.first, in.last, in.more, in.vv)
+				vv, proto, done, err := f.Process(in.id, in.first, in.last, in.more, in.proto, in.vv)
 				if err != nil {
-					t.Fatalf("f.Process(%+v, %+d, %+d, %t, %+v) failed: %v", in.id, in.first, in.last, in.more, in.vv, err)
+					t.Fatalf("f.Process(%+v, %d, %d, %t, %d, %X) failed: %s",
+						in.id, in.first, in.last, in.more, in.proto, in.vv.ToView(), err)
 				}
 				if !reflect.DeepEqual(vv, c.out[i].vv) {
-					t.Errorf("got Process(%d) = %+v, want = %+v", i, vv, c.out[i].vv)
+					t.Errorf("got Process(%+v, %d, %d, %t, %d, %X) = (%X, _, _, _), want = (%X, _, _, _)",
+						in.id, in.first, in.last, in.more, in.proto, in.vv.ToView(), vv.ToView(), c.out[i].vv.ToView())
 				}
 				if done != c.out[i].done {
-					t.Errorf("got Process(%d) = %+v, want = %+v", i, done, c.out[i].done)
+					t.Errorf("got Process(%+v, %d, %d, %t, %d, _) = (_, _, %t, _), want = (_, _, %t, _)",
+						in.id, in.first, in.last, in.more, in.proto, done, c.out[i].done)
 				}
 				if c.out[i].done {
+					if firstFragmentProto != proto {
+						t.Errorf("got Process(%+v, %d, %d, %t, %d, _) = (_, %d, _, _), want = (_, %d, _, _)",
+							in.id, in.first, in.last, in.more, in.proto, proto, firstFragmentProto)
+					}
 					if _, ok := f.reassemblers[in.id]; ok {
 						t.Errorf("Process(%d) did not remove buffer from reassemblers", i)
 					}
@@ -113,14 +134,14 @@ func TestReassemblingTimeout(t *testing.T) {
 	timeout := time.Millisecond
 	f := NewFragmentation(minBlockSize, 1024, 512, timeout)
 	// Send first fragment with id = 0, first = 0, last = 0, and more = true.
-	f.Process(FragmentID{}, 0, 0, true, vv(1, "0"))
+	f.Process(FragmentID{}, 0, 0, true, 0xFF, vv(1, "0"))
 	// Sleep more than the timeout.
 	time.Sleep(2 * timeout)
 	// Send another fragment that completes a packet.
 	// However, no packet should be reassembled because the fragment arrived after the timeout.
-	_, done, err := f.Process(FragmentID{}, 1, 1, false, vv(1, "1"))
+	_, _, done, err := f.Process(FragmentID{}, 1, 1, false, 0xFF, vv(1, "1"))
 	if err != nil {
-		t.Fatalf("f.Process(0, 1, 1, false, vv(1, \"1\")) failed: %v", err)
+		t.Fatalf("f.Process(0, 1, 1, false, 0xFF, vv(1, \"1\")) failed: %v", err)
 	}
 	if done {
 		t.Errorf("Fragmentation does not respect the reassembling timeout.")
@@ -130,15 +151,15 @@ func TestReassemblingTimeout(t *testing.T) {
 func TestMemoryLimits(t *testing.T) {
 	f := NewFragmentation(minBlockSize, 3, 1, DefaultReassembleTimeout)
 	// Send first fragment with id = 0.
-	f.Process(FragmentID{ID: 0}, 0, 0, true, vv(1, "0"))
+	f.Process(FragmentID{ID: 0}, 0, 0, true, 0xFF, vv(1, "0"))
 	// Send first fragment with id = 1.
-	f.Process(FragmentID{ID: 1}, 0, 0, true, vv(1, "1"))
+	f.Process(FragmentID{ID: 1}, 0, 0, true, 0xFF, vv(1, "1"))
 	// Send first fragment with id = 2.
-	f.Process(FragmentID{ID: 2}, 0, 0, true, vv(1, "2"))
+	f.Process(FragmentID{ID: 2}, 0, 0, true, 0xFF, vv(1, "2"))
 
 	// Send first fragment with id = 3. This should caused id = 0 and id = 1 to be
 	// evicted.
-	f.Process(FragmentID{ID: 3}, 0, 0, true, vv(1, "3"))
+	f.Process(FragmentID{ID: 3}, 0, 0, true, 0xFF, vv(1, "3"))
 
 	if _, ok := f.reassemblers[FragmentID{ID: 0}]; ok {
 		t.Errorf("Memory limits are not respected: id=0 has not been evicted.")
@@ -154,9 +175,9 @@ func TestMemoryLimits(t *testing.T) {
 func TestMemoryLimitsIgnoresDuplicates(t *testing.T) {
 	f := NewFragmentation(minBlockSize, 1, 0, DefaultReassembleTimeout)
 	// Send first fragment with id = 0.
-	f.Process(FragmentID{}, 0, 0, true, vv(1, "0"))
+	f.Process(FragmentID{}, 0, 0, true, 0xFF, vv(1, "0"))
 	// Send the same packet again.
-	f.Process(FragmentID{}, 0, 0, true, vv(1, "0"))
+	f.Process(FragmentID{}, 0, 0, true, 0xFF, vv(1, "0"))
 
 	got := f.size
 	want := 1
@@ -248,12 +269,12 @@ func TestErrors(t *testing.T) {
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			f := NewFragmentation(test.blockSize, HighFragThreshold, LowFragThreshold, DefaultReassembleTimeout)
-			_, done, err := f.Process(FragmentID{}, test.first, test.last, test.more, vv(len(test.data), test.data))
+			_, _, done, err := f.Process(FragmentID{}, test.first, test.last, test.more, 0, vv(len(test.data), test.data))
 			if !errors.Is(err, test.err) {
-				t.Errorf("got Proceess(_, %d, %d, %t, %q) = (_, _, %v), want = (_, _, %v)", test.first, test.last, test.more, test.data, err, test.err)
+				t.Errorf("got Process(_, %d, %d, %t, _, %q) = (_, _, _, %v), want = (_, _, _, %v)", test.first, test.last, test.more, test.data, err, test.err)
 			}
 			if done {
-				t.Errorf("got Proceess(_, %d, %d, %t, %q) = (_, true, _), want = (_, false, _)", test.first, test.last, test.more, test.data)
+				t.Errorf("got Process(_, %d, %d, %t, _, %q) = (_, _, true, _), want = (_, _, false, _)", test.first, test.last, test.more, test.data)
 			}
 		})
 	}
diff --git a/pkg/tcpip/network/fragmentation/reassembler.go b/pkg/tcpip/network/fragmentation/reassembler.go
index 50d30bbf0..f044867dc 100644
--- a/pkg/tcpip/network/fragmentation/reassembler.go
+++ b/pkg/tcpip/network/fragmentation/reassembler.go
@@ -34,6 +34,7 @@ type reassembler struct {
 	reassemblerEntry
 	id           FragmentID
 	size         int
+	proto        uint8
 	mu           sync.Mutex
 	holes        []hole
 	deleted      int
@@ -46,7 +47,6 @@ func newReassembler(id FragmentID) *reassembler {
 	r := &reassembler{
 		id:           id,
 		holes:        make([]hole, 0, 16),
-		deleted:      0,
 		heap:         make(fragHeap, 0, 8),
 		creationTime: time.Now(),
 	}
@@ -78,7 +78,7 @@ func (r *reassembler) updateHoles(first, last uint16, more bool) bool {
 	return used
 }
 
-func (r *reassembler) process(first, last uint16, more bool, vv buffer.VectorisedView) (buffer.VectorisedView, bool, int, error) {
+func (r *reassembler) process(first, last uint16, more bool, proto uint8, vv buffer.VectorisedView) (buffer.VectorisedView, uint8, bool, int, error) {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 	consumed := 0
@@ -86,7 +86,18 @@ func (r *reassembler) process(first, last uint16, more bool, vv buffer.Vectorise
 		// A concurrent goroutine might have already reassembled
 		// the packet and emptied the heap while this goroutine
 		// was waiting on the mutex. We don't have to do anything in this case.
-		return buffer.VectorisedView{}, false, consumed, nil
+		return buffer.VectorisedView{}, 0, false, consumed, nil
+	}
+	// For IPv6, it is possible to have different Protocol values between
+	// fragments of a packet (because, unlike IPv4, the Protocol is not used to
+	// identify a fragment). In this case, only the Protocol of the first
+	// fragment must be used as per RFC 8200 Section 4.5.
+	//
+	// TODO(gvisor.dev/issue/3648): The entire first IP header should be recorded
+	// here (instead of just the protocol) because most IP options should be
+	// derived from the first fragment.
+	if first == 0 {
+		r.proto = proto
 	}
 	if r.updateHoles(first, last, more) {
 		// We store the incoming packet only if it filled some holes.
@@ -96,13 +107,13 @@ func (r *reassembler) process(first, last uint16, more bool, vv buffer.Vectorise
 	}
 	// Check if all the holes have been deleted and we are ready to reassamble.
 	if r.deleted < len(r.holes) {
-		return buffer.VectorisedView{}, false, consumed, nil
+		return buffer.VectorisedView{}, 0, false, consumed, nil
 	}
 	res, err := r.heap.reassemble()
 	if err != nil {
-		return buffer.VectorisedView{}, false, consumed, fmt.Errorf("fragment reassembly failed: %v", err)
+		return buffer.VectorisedView{}, 0, false, consumed, fmt.Errorf("fragment reassembly failed: %w", err)
 	}
-	return res, true, consumed, nil
+	return res, r.proto, true, consumed, nil
 }
 
 func (r *reassembler) tooOld(timeout time.Duration) bool {