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net/packet: add NAT support for DCCP and GRE

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Updates tailscale/corp#8020

Signed-off-by: Maisem Ali <maisem@tailscale.com>
This commit is contained in:
Maisem Ali
2023-04-24 11:54:25 -07:00
committed by Maisem Ali
parent ce11c82d51
commit f58751eb2b
3 changed files with 53 additions and 11 deletions
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45
net/packet/packet.go
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@ -558,19 +558,42 @@ func withPort(ap netip.AddrPort, port uint16) netip.AddrPort {
// Currently (2023-03-01) only TCP/UDP/ICMP over IPv4 is supported.
// p is modified in place.
// If p.IPProto is unknown, only the IP header checksum is updated.
// TODO(maisem): more protocols (sctp, gre, dccp)
func updateV4PacketChecksums(p *Parsed, old, new netip.Addr) {
o4, n4 := old.As4(), new.As4()
updateV4Checksum(p.Buffer()[10:12], o4[:], n4[:]) // header
switch p.IPProto {
case ipproto.UDP:
updateV4Checksum(p.Transport()[6:8], o4[:], n4[:])
case ipproto.TCP:
updateV4Checksum(p.Transport()[16:18], o4[:], n4[:])
case ipproto.ICMPv4:
// Nothing to do.
if len(p.Buffer()) < 12 {
// Not enough space for an IPv4 header.
return
}
o4, n4 := old.As4(), new.As4()
// First update the checksum in the IP header.
updateV4Checksum(p.Buffer()[10:12], o4[:], n4[:])
// Now update the transport layer checksums, where applicable.
tr := p.Transport()
switch p.IPProto {
case ipproto.UDP, ipproto.DCCP:
if len(tr) < 8 {
// Not enough space for a UDP header.
return
}
updateV4Checksum(tr[6:8], o4[:], n4[:])
case ipproto.TCP:
if len(tr) < 18 {
// Not enough space for a TCP header.
return
}
updateV4Checksum(tr[16:18], o4[:], n4[:])
case ipproto.GRE:
if len(tr) < 6 {
// Not enough space for a GRE header.
return
}
if tr[0] == 1 { // checksum present
updateV4Checksum(tr[4:6], o4[:], n4[:])
}
case ipproto.SCTP, ipproto.ICMPv4:
// No transport layer update required.
}
// TODO(maisem): more protocols (sctp, gre, dccp)
}
// updateV4Checksum calculates and updates the checksum in the packet buffer for