ICMPv4 EchoReply packet's checksum is wrong

[buptczq]

The checksum of echo packet is set here for raw socket:

netstack/tcpip/network/ipv4/icmp.go

Lines 91 to 93 in fe7dc38

	// It's possible that a raw socket expects to receive this.
	h.SetChecksum(wantChecksum)
	e.dispatcher.DeliverTransportPacket(r, header.ICMPv4ProtocolNumber, netHeader, vv)

The checksum of reply packet is calculated here without clearing the checksum in header:

netstack/tcpip/network/ipv4/icmp.go

Lines 99 to 101 in fe7dc38

	copy(pkt, h)
	pkt.SetType(header.ICMPv4EchoReply)
	pkt.SetChecksum(^header.Checksum(pkt, header.ChecksumVV(vv, 0)))

Is it should be written as the following?

		pkt.SetType(header.ICMPv4EchoReply)
		// Clear the checksum
		pkt.SetChecksum(0)
		pkt.SetChecksum(^header.Checksum(pkt, header.ChecksumVV(vv, 0)))

[hbhasker]

Do you mind refiling this under github.com/google/gvisor. This repo is a read-only fork of the netstack included in gVisor. This repo is not usually actively monitored nor do we directly commit to this repo.