webnet/tailscale
1
0
Fork 0
Code Issues Pull Requests 3 Packages Projects Releases Wiki Activity

net/packet, wgengine/netstack: remove workaround for old gvisor ECN bug

Browse Source 
Fixes #2642

Change-Id: Ic02251d24a4109679645d1c8336e0f961d0cce13
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
2022-03-26 21:13:55 -07:00
committed by Brad Fitzpatrick
parent 5a44f9f5b5
commit e4d8d5e78b
3 changed files with 0 additions and 114 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/packet/packet.go
-57
View File
@@ -434,40 +434,6 @@ func (q *Parsed) IsEchoResponse() bool {
}
}
// RemoveECNBits modifies p and its underlying memory buffer to remove
// ECN bits, if any. It reports whether it did so.
//
// It currently only does the TCP flags.
func (p *Parsed) RemoveECNBits() bool {
if p.IPVersion == 0 {
return false
}
if p.IPProto != ipproto.TCP {
// TODO(bradfitz): handle non-TCP too? for now only trying to
// fix the Issue 2642 problem.
return false
}
if p.TCPFlags&TCPECNBits == 0 {
// Nothing to do.
return false
}
// Clear flags.
// First in the parsed output.
p.TCPFlags = p.TCPFlags & ^TCPECNBits
// Then in the underlying memory.
tcp := p.Transport()
old := binary.BigEndian.Uint16(tcp[12:14])
tcp[13] = byte(p.TCPFlags)
new := binary.BigEndian.Uint16(tcp[12:14])
oldSum := binary.BigEndian.Uint16(tcp[16:18])
newSum := ^checksumUpdate2ByteAlignedUint16(^oldSum, old, new)
binary.BigEndian.PutUint16(tcp[16:18], newSum)
return true
}
func Hexdump(b []byte) string {
out := new(strings.Builder)
for i := 0; i < len(b); i += 16 {
@@ -499,26 +465,3 @@ func Hexdump(b []byte) string {
}
return out.String()
}
// From gVisor's unexported API:
// checksumUpdate2ByteAlignedUint16 updates a uint16 value in a calculated
// checksum.
//
// The value MUST begin at a 2-byte boundary in the original buffer.
func checksumUpdate2ByteAlignedUint16(xsum, old, new uint16) uint16 {
// As per RFC 1071 page 4,
//(4) Incremental Update
//
// ...
//
// To update the checksum, simply add the differences of the
// sixteen bit integers that have been changed. To see why this
// works, observe that every 16-bit integer has an additive inverse
// and that addition is associative. From this it follows that
// given the original value m, the new value m', and the old
// checksum C, the new checksum C' is:
//
// C' = C + (-m) + m' = C + (m' - m)
return checksumCombine(xsum, checksumCombine(new, ^old))
}