Commit d8183ff9 authored by David Fifield's avatar David Fifield
Browse files

Dial the (Ext)ORPort with a random srcaddr in 127.0.1.0/24. 

This is a hack to attempt to conserve emphemeral port numbers.
https://bugs.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/40198#note_2839248
https://lists.torproject.org/pipermail/anti-censorship-team/2022-September/000263.html
parent 624ce556

go.mod

+2 −0
Original line number Diff line number Diff line
@@ -22,3 +22,5 @@ require ( 
	golang.org/x/net v0.0.0-20220425223048-2871e0cb64e4

	google.golang.org/protobuf v1.26.0

)



replace git.torproject.org/pluggable-transports/goptlib.git v1.1.0 => gitlab.torproject.org/dcf/goptlib v0.0.0-20220930193603-cd79bbc900ad

go.sum

+2 −2
Original line number Diff line number Diff line 
cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=

cloud.google.com/go v0.34.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=

git.torproject.org/pluggable-transports/goptlib.git v1.1.0 h1:LMQAA8pAho+QtYrrVNimJQiINNEwcwuuD99vezD/PAo=

git.torproject.org/pluggable-transports/goptlib.git v1.1.0/go.mod h1:YT4XMSkuEXbtqlydr9+OxqFAyspUv0Gr9qhM3B++o/Q=

github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=

github.com/Knetic/govaluate v3.0.1-0.20171022003610-9aa49832a739+incompatible/go.mod h1:r7JcOSlj0wfOMncg0iLm8Leh48TZaKVeNIfJntJ2wa0=

github.com/Shopify/sarama v1.19.0/go.mod h1:FVkBWblsNy7DGZRfXLU0O9RCGt5g3g3yEuWXgklEdEo=
@@ -356,6 +354,8 @@ github.com/xtaci/smux v1.5.15/go.mod h1:OMlQbT5vcgl2gb49mFkYo6SMf+zP3rcjcwQz7ZU7 
github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=

github.com/yuin/goldmark v1.1.32/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=

github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=

gitlab.torproject.org/dcf/goptlib v0.0.0-20220930193603-cd79bbc900ad h1:n3z4mhfahnulwrQRoKR0vJHFdxHSgztu+YVNRFJCYp8=

gitlab.torproject.org/dcf/goptlib v0.0.0-20220930193603-cd79bbc900ad/go.mod h1:4PBMl1dg7/3vMWSoWb46eGWlrxkUyn/CAJmxhDLAlDs=

gitlab.torproject.org/tpo/anti-censorship/geoip v0.0.0-20210928150955-7ce4b3d98d01 h1:4949mHh9Vj2/okk48yG8nhP6TosFWOUfSfSr502sKGE=

gitlab.torproject.org/tpo/anti-censorship/geoip v0.0.0-20210928150955-7ce4b3d98d01/go.mod h1:K3LOI4H8fa6j+7E10ViHeGEQV10304FG4j94ypmKLjY=

go.etcd.io/bbolt v1.3.3/go.mod h1:IbVyRI1SCnLcuJnV2u8VeU0CEYM7e686BmAb1XKL+uU=

server/server.go

+19 −2
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ import ( 
	"io"

	"io/ioutil"

	"log"

	"math/rand"

	"net"

	"net/http"

	"os"
@@ -67,16 +68,32 @@ func proxy(local *net.TCPConn, conn net.Conn) { 
	wg.Wait()

}



// localAddr returns a random localhost IP address, suitable to be used as the

// LocalAddr in a net.Dialer in a call to pt.DialOrWithDialer.

//

// The reason for using multiple source addresses when dialing the ORPort is to

// conserve ephemeral ports:

// https://bugs.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/40198

func localAddr() net.Addr {

	var b byte

	for b == 0 {

		b = byte(rand.Uint32())

	}

	return &net.TCPAddr{IP: net.IPv4(127, 0, 1, b)}

}



// handleConn bidirectionally connects a client snowflake connection with an ORPort.

func handleConn(conn net.Conn) error {

	addr := conn.RemoteAddr().String()

	statsChannel <- addr != ""

	or, err := pt.DialOr(&ptInfo, addr, ptMethodName)

	or, err := pt.DialOrWithDialer(&net.Dialer{

		LocalAddr: localAddr(),

	}, &ptInfo, addr, ptMethodName)

	if err != nil {

		return fmt.Errorf("failed to connect to ORPort: %s", err)

	}

	defer or.Close()

	proxy(or, conn)

	proxy(or.(*net.TCPConn), conn)

	return nil

}