Avoid memory leaks

Properly discard segments from the segment heap.

PiperOrigin-RevId: 298704074

pkg/tcpip/transport/tcp/rcv.go

@@ -195,6 +195,10 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 
 		for i := first; i < len(r.pendingRcvdSegments); i++ {
 			r.pendingRcvdSegments[i].decRef()
+			// Note that slice truncation does not allow garbage collection of
+			// truncated items, thus truncated items must be set to nil to avoid
+			// memory leaks.
+			r.pendingRcvdSegments[i] = nil
 		}
 		r.pendingRcvdSegments = r.pendingRcvdSegments[:first]
 

pkg/tcpip/transport/tcp/segment_heap.go

@@ -41,6 +41,7 @@ func (h *segmentHeap) Pop() interface{} {
 	old := *h
 	n := len(old)
 	x := old[n-1]
+	old[n-1] = nil
 	*h = old[:n-1]
 	return x
 }