@ -10,6 +10,8 @@ import (
"net/netip"
"strings"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/header"
"tailscale.com/net/netaddr"
"tailscale.com/types/ipproto"
)
@ -453,11 +455,14 @@ func (q *Parsed) IsEchoResponse() bool {
}
// UpdateSrcAddr updates the source address in the packet buffer (e.g. during
// SNAT). It also updates the checksum. Currently (2022-12-10) only TCP/UDP/ICMP
// over IPv4 is supported. It panics if called with IPv6 addr.
// SNAT). It also updates the checksum. Currently (2023-09-22) only TCP/UDP/ICMP
// is supported. It panics if provided with an address in a different
// family to the parsed packet.
func ( q * Parsed ) UpdateSrcAddr ( src netip . Addr ) {
if q . IPVersion != 4 || src . Is6 ( ) {
panic ( "UpdateSrcAddr: only IPv4 is supported" )
if src . Is6 ( ) && q . IPVersion != 6 {
panic ( "UpdateSrcAddr: cannot write IPv6 address to v4 packet" )
} else if src . Is4 ( ) && q . IPVersion != 4 {
panic ( "UpdateSrcAddr: cannot write IPv4 address to v6 packet" )
}
q . CaptureMeta . DidSNAT = true
q . CaptureMeta . OriginalSrc = q . Src
@ -466,19 +471,27 @@ func (q *Parsed) UpdateSrcAddr(src netip.Addr) {
q . Src = netip . AddrPortFrom ( src , q . Src . Port ( ) )
b := q . Buffer ( )
v4 := src . As4 ( )
copy ( b [ 12 : 16 ] , v4 [ : ] )
updateV4PacketChecksums ( q , old , src )
if src . Is6 ( ) {
v6 := src . As16 ( )
copy ( b [ 8 : 24 ] , v6 [ : ] )
updateV6PacketChecksums ( q , old , src )
} else {
v4 := src . As4 ( )
copy ( b [ 12 : 16 ] , v4 [ : ] )
updateV4PacketChecksums ( q , old , src )
}
}
// UpdateDstAddr updates the source address in the packet buffer (e.g. during
// UpdateDstAddr updates the destination address in the packet buffer (e.g. during
// DNAT). It also updates the checksum. Currently (2022-12-10) only TCP/UDP/ICMP
// over IPv4 is supported. It panics if called with IPv6 addr.
// is supported. It panics if provided with an address in a different
// family to the parsed packet.
func ( q * Parsed ) UpdateDstAddr ( dst netip . Addr ) {
if q . IPVersion != 4 || dst . Is6 ( ) {
panic ( "UpdateDstAddr: only IPv4 is supported" )
if dst . Is6 ( ) && q . IPVersion != 6 {
panic ( "UpdateDstAddr: cannot write IPv6 address to v4 packet" )
} else if dst . Is4 ( ) && q . IPVersion != 4 {
panic ( "UpdateDstAddr: cannot write IPv4 address to v6 packet" )
}
q . CaptureMeta . DidDNAT = true
q . CaptureMeta . OriginalDst = q . Dst
@ -486,9 +499,15 @@ func (q *Parsed) UpdateDstAddr(dst netip.Addr) {
q . Dst = netip . AddrPortFrom ( dst , q . Dst . Port ( ) )
b := q . Buffer ( )
v4 := dst . As4 ( )
copy ( b [ 16 : 20 ] , v4 [ : ] )
updateV4PacketChecksums ( q , old , dst )
if dst . Is6 ( ) {
v6 := dst . As16 ( )
copy ( b [ 24 : 36 ] , v6 [ : ] )
updateV6PacketChecksums ( q , old , dst )
} else {
v4 := dst . As4 ( )
copy ( b [ 16 : 20 ] , v4 [ : ] )
updateV4PacketChecksums ( q , old , dst )
}
}
// EchoIDSeq extracts the identifier/sequence bytes from an ICMP Echo response,
@ -572,13 +591,13 @@ func updateV4PacketChecksums(p *Parsed, old, new netip.Addr) {
tr := p . Transport ( )
switch p . IPProto {
case ipproto . UDP , ipproto . DCCP :
if len ( tr ) < 8 {
if len ( tr ) < header . UDPMinimumSize {
// Not enough space for a UDP header.
return
}
updateV4Checksum ( tr [ 6 : 8 ] , o4 [ : ] , n4 [ : ] )
case ipproto . TCP :
if len ( tr ) < 18 {
if len ( tr ) < header . TCPMinimumSize {
// Not enough space for a TCP header.
return
}
@ -596,6 +615,39 @@ func updateV4PacketChecksums(p *Parsed, old, new netip.Addr) {
}
}
// updateV6PacketChecksums updates the checksums in the packet buffer.
// p is modified in place.
// If p.IPProto is unknown, no checksums are updated.
func updateV6PacketChecksums ( p * Parsed , old , new netip . Addr ) {
if len ( p . Buffer ( ) ) < 40 {
// Not enough space for an IPv6 header.
return
}
o6 , n6 := tcpip . AddrFrom16Slice ( old . AsSlice ( ) ) , tcpip . AddrFrom16Slice ( new . AsSlice ( ) )
// Now update the transport layer checksums, where applicable.
tr := p . Transport ( )
switch p . IPProto {
case ipproto . ICMPv6 :
if len ( tr ) < header . ICMPv6MinimumSize {
return
}
header . ICMPv6 ( tr ) . UpdateChecksumPseudoHeaderAddress ( o6 , n6 )
case ipproto . UDP , ipproto . DCCP :
if len ( tr ) < header . UDPMinimumSize {
return
}
header . UDP ( tr ) . UpdateChecksumPseudoHeaderAddress ( o6 , n6 , true )
case ipproto . TCP :
if len ( tr ) < header . TCPMinimumSize {
return
}
header . TCP ( tr ) . UpdateChecksumPseudoHeaderAddress ( o6 , n6 , true )
case ipproto . SCTP :
// No transport layer update required.
}
}
// updateV4Checksum calculates and updates the checksum in the packet buffer for
// a change between old and new. The oldSum must point to the 16-bit checksum
// field in the packet buffer that holds the old checksum value, it will be
Tom DNetto
1 year ago
committed by