commit 611205be681322883a4d73dd00fcb13c4352fe53 Author: Yawning Angel yawning@torproject.org Date: Thu Oct 29 17:29:21 2015 +0000

Add the "meek_lite" transport, which does what one would expect.

This is a meek client only implementation, with the following differences with dcf's `meek-client`:

- It is named `meek_lite` to differentiate it from the real thing. - It does not support using an external helper to normalize TLS signatures, so adversaries can look for someone using the Go TLS library to do HTTP. - It does the right thing with TOR_PT_PROXY, even when a helper is not present.

Most of the credit goes to dcf, who's code I librerally cribbed and stole. It is intended primarily as a "better than nothina" option for enviornments that do not or can not presently use an external Firefox helper. --- ChangeLog | 4 + doc/obfs4proxy.1 | 4 +- transports/meeklite/base.go | 89 +++++++++++ transports/meeklite/meek.go | 358 +++++++++++++++++++++++++++++++++++++++++++ transports/transports.go | 2 + 5 files changed, 455 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog index 774be88..1d04d8d 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,6 +1,10 @@ Changes in version 0.0.6 - UNRELEASED: - Delay transport factory initialization till after logging has been initialized. + - Add a meek client implementation (WARNING: Does not support using a + helper to normalize TLS signatures). The brave people that want to use + it can do so as the "meek_lite" transport, with identical bridge lines + to the real meek-client.

Changes in version 0.0.5 - 2015-04-15: - Go vet/fmt fixes, and misc. code cleanups. Patches by mvdan. diff --git a/doc/obfs4proxy.1 b/doc/obfs4proxy.1 index 9fb5f28..13b89fd 100644 --- a/doc/obfs4proxy.1 +++ b/doc/obfs4proxy.1 @@ -1,4 +1,4 @@ -.TH OBFS4PROXY 1 "2015-04-03" +.TH OBFS4PROXY 1 "2015-10-29" .SH NAME obfs4proxy - pluggable transport proxy for Tor, implementing obfs4 .SH SYNOPSIS @@ -12,7 +12,7 @@ will see innocent-looking transformed traffic instead of the actual Tor traffic. .PP obfs4proxy implements the obfuscation protocols obfs2, obfs3, -ScrambleSuit (client only) and obfs4. +ScrambleSuit (client only), meek (client only) and obfs4. .PP obfs4proxy is currently only supported as a managed pluggable transport spawned as a helper process via the \fBtor\fR daemon. diff --git a/transports/meeklite/base.go b/transports/meeklite/base.go new file mode 100644 index 0000000..2a4cf80 --- /dev/null +++ b/transports/meeklite/base.go @@ -0,0 +1,89 @@ +/* + * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org> + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are met: + * + * * Redistributions of source code must retain the above copyright notice, + * this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright notice, + * this list of conditions and the following disclaimer in the documentation + * and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + */ + +// Package meeklite provides an implementation of the Meek circumvention +// protocol. Only a client implementation is provided, and no effort is +// made to normalize the TLS fingerprint. +// +// It borrows quite liberally from the real meek-client code. +package meeklite + +import ( + "fmt" + "net" + + "git.torproject.org/pluggable-transports/goptlib.git" + "git.torproject.org/pluggable-transports/obfs4.git/transports/base" +) + +const transportName = "meek_lite" + +// Transport is the Meek implementation of the base.Transport interface. +type Transport struct{} + +// Name returns the name of the Meek transport protocol. +func (t *Transport) Name() string { + return transportName +} + +// ClientFactory returns a new meekClientFactory instance. +func (t *Transport) ClientFactory(stateDir string) (base.ClientFactory, error) { + cf := &meekClientFactory{transport: t} + return cf, nil +} + +// ServerFactory will one day return a new meekServerFactory instance. +func (t *Transport) ServerFactory(stateDir string, args *pt.Args) (base.ServerFactory, error) { + // TODO: Fill this in eventually, though for servers people should + // just use the real thing. + return nil, fmt.Errorf("server not supported") +} + +type meekClientFactory struct { + transport base.Transport +} + +func (cf *meekClientFactory) Transport() base.Transport { + return cf.transport +} + +func (cf *meekClientFactory) ParseArgs(args *pt.Args) (interface{}, error) { + return newClientArgs(args) +} + +func (cf *meekClientFactory) Dial(network, addr string, dialFn base.DialFunc, args interface{}) (net.Conn, error) { + // Validate args before opening outgoing connection. + ca, ok := args.(*meekClientArgs) + if !ok { + return nil, fmt.Errorf("invalid argument type for args") + } + + return newMeekConn(network, addr, dialFn, ca) +} + +var _ base.ClientFactory = (*meekClientFactory)(nil) +var _ base.Transport = (*Transport)(nil) diff --git a/transports/meeklite/meek.go b/transports/meeklite/meek.go new file mode 100644 index 0000000..5842704 --- /dev/null +++ b/transports/meeklite/meek.go @@ -0,0 +1,358 @@ +/* + * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org> + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are met: + * + * * Redistributions of source code must retain the above copyright notice, + * this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright notice, + * this list of conditions and the following disclaimer in the documentation + * and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + */ + +package meeklite + +import ( + "bytes" + "crypto/rand" + "crypto/sha256" + "encoding/hex" + "errors" + "fmt" + "io" + "io/ioutil" + "net" + "net/http" + gourl "net/url" + "runtime" + "sync" + "time" + + "git.torproject.org/pluggable-transports/goptlib.git" + "git.torproject.org/pluggable-transports/obfs4.git/transports/base" +) + +const ( + urlArg = "url" + frontArg = "front" + + maxChanBacklog = 16 + + // Constants shamelessly stolen from meek-client.go... + maxPayloadLength = 0x10000 + initPollInterval = 100 * time.Millisecond + maxPollInterval = 5 * time.Second + pollIntervalMultiplier = 1.5 + maxRetries = 10 + retryDelay = 30 * time.Second +) + +var ( + // ErrNotSupported is the error returned for a unsupported operation. + ErrNotSupported = errors.New("meek_lite: operation not supported") + + loopbackAddr = net.IPv4(127, 0, 0, 1) +) + +type meekClientArgs struct { + url *gourl.URL + front string +} + +func (ca *meekClientArgs) Network() string { + return transportName +} + +func (ca *meekClientArgs) String() string { + return transportName + ":" + ca.front + ":" + ca.url.String() +} + +func newClientArgs(args *pt.Args) (ca *meekClientArgs, err error) { + ca = &meekClientArgs{} + + // Parse the URL argument. + str, ok := args.Get(urlArg) + if !ok { + return nil, fmt.Errorf("missing argument '%s'", urlArg) + } + ca.url, err = gourl.Parse(str) + if err != nil { + return nil, fmt.Errorf("malformed url: '%s'", str) + } + switch ca.url.Scheme { + case "http", "https": + default: + return nil, fmt.Errorf("invalid scheme: '%s'", ca.url.Scheme) + } + + // Parse the (optional) front argument. + ca.front, _ = args.Get(frontArg) + + return ca, nil +} + +type meekConn struct { + sync.Mutex + + args *meekClientArgs + sessionID string + transport *http.Transport + + workerRunning bool + workerWrChan chan []byte + workerRdChan chan []byte + workerCloseChan chan bool + rdBuf *bytes.Buffer +} + +func (c *meekConn) Read(p []byte) (n int, err error) { + // If there is data left over from the previous read, + // service the request using the buffered data. + if c.rdBuf != nil { + if c.rdBuf.Len() == 0 { + panic("empty read buffer") + } + n, err = c.rdBuf.Read(p) + if c.rdBuf.Len() == 0 { + c.rdBuf = nil + } + return + } + + // Wait for the worker to enqueue more incoming data. + b, ok := <-c.workerRdChan + if !ok { + // Close() was called and the worker's shutting down. + return 0, io.ErrClosedPipe + } + + // Ew, an extra copy, but who am I kidding, it's meek. + buf := bytes.NewBuffer(b) + n, err = buf.Read(p) + if buf.Len() > 0 { + // If there's data pending, stash the buffer so the next + // Read() call will use it to fulfuill the Read(). + c.rdBuf = buf + } + return +} + +func (c *meekConn) Write(b []byte) (n int, err error) { + // Check to see if the connection is actually open. + c.Lock() + closed := !c.workerRunning + c.Unlock() + if closed { + return 0, io.ErrClosedPipe + } + + if len(b) > 0 { + // Copy the data to be written to a new slice, since + // we return immediately after queuing and the peer can + // happily reuse `b` before data has been sent. + toWrite := len(b) + b2 := make([]byte, toWrite) + copy(b2, b) + offset := 0 + for toWrite > 0 { + // Chunk up the writes to keep them under the maximum + // payload length. + sz := toWrite + if sz > maxPayloadLength { + sz = maxPayloadLength + } + + // Enqueue a properly sized subslice of our copy. + if ok := c.enqueueWrite(b2[offset : offset+sz]); !ok { + // Technically we did enqueue data, but the worker's + // got closed out from under us. + return 0, io.ErrClosedPipe + } + toWrite -= sz + offset += sz + runtime.Gosched() + } + } + return len(b), nil +} + +func (c *meekConn) Close() error { + // Ensure that we do this once and only once. + c.Lock() + defer c.Unlock() + if !c.workerRunning { + return nil + } + + // Tear down the worker. + c.workerRunning = false + c.workerCloseChan <- true + + return nil +} + +func (c *meekConn) LocalAddr() net.Addr { + return &net.IPAddr{IP: loopbackAddr} +} + +func (c *meekConn) RemoteAddr() net.Addr { + return c.args +} + +func (c *meekConn) SetDeadline(t time.Time) error { + return ErrNotSupported +} + +func (c *meekConn) SetReadDeadline(t time.Time) error { + return ErrNotSupported +} + +func (c *meekConn) SetWriteDeadline(t time.Time) error { + return ErrNotSupported +} + +func (c *meekConn) enqueueWrite(b []byte) (ok bool) { + defer func() { recover() }() + c.workerWrChan <- b + return true +} + +func (c *meekConn) roundTrip(sndBuf []byte) (recvBuf []byte, err error) { + var req *http.Request + var resp *http.Response + + for retries := 0; retries < maxRetries; retries++ { + url := *c.args.url + host := url.Host + if c.args.front != "" { + url.Host = c.args.front + } + req, err = http.NewRequest("POST", url.String(), bytes.NewReader(sndBuf)) + if err != nil { + return nil, err + } + if c.args.front != "" { + req.Host = host + } + req.Header.Set("X-Session-Id", c.sessionID) + + resp, err = c.transport.RoundTrip(req) + if err != nil { + return nil, err + } + if resp.StatusCode != http.StatusOK { + err = fmt.Errorf("status code was %d, not %d", resp.StatusCode, http.StatusOK) + time.Sleep(retryDelay) + } else { + defer resp.Body.Close() + recvBuf, err = ioutil.ReadAll(io.LimitReader(resp.Body, maxPayloadLength)) + return + } + } + return +} + +func (c *meekConn) ioWorker() { + interval := initPollInterval +loop: + for { + var sndBuf []byte + select { + case <-time.After(interval): + // If the poll interval has elapsed, issue a request. + case sndBuf = <-c.workerWrChan: + // If there is data pending a send, issue a request. + case _ = <-c.workerCloseChan: + break loop + } + + // Issue a request. + rdBuf, err := c.roundTrip(sndBuf) + if err != nil { + // Welp, something went horrifically wrong. + break loop + } + if len(rdBuf) > 0 { + // Received data, enqueue the read. + c.workerRdChan <- rdBuf + + // And poll immediately. + interval = 0 + } else if sndBuf != nil { + // Sent data, poll immediately. + interval = 0 + } else if interval == 0 { + // Neither sent nor received data, initialize the delay. + interval = initPollInterval + } else { + // Apply a multiplicative backoff. + interval = time.Duration(float64(interval) * pollIntervalMultiplier) + if interval > maxPollInterval { + interval = maxPollInterval + } + } + + runtime.Gosched() + } + + // Unblock callers waiting in Read() for data that will never arrive, + // and callers waiting in Write() for data that will never get sent. + close(c.workerRdChan) + close(c.workerWrChan) + + // In case the close was done on an error condition, update the state + // variable so that further calls to Write() will fail. + c.Lock() + defer c.Unlock() + c.workerRunning = false +} + +func newMeekConn(network, addr string, dialFn base.DialFunc, ca *meekClientArgs) (net.Conn, error) { + id, err := newSessionID() + if err != nil { + return nil, err + } + + tr := &http.Transport{Dial: dialFn} + conn := &meekConn{ + args: ca, + sessionID: id, + transport: tr, + workerRunning: true, + workerWrChan: make(chan []byte, maxChanBacklog), + workerRdChan: make(chan []byte, maxChanBacklog), + workerCloseChan: make(chan bool), + } + + // Start the I/O worker. + go conn.ioWorker() + + return conn, nil +} + +func newSessionID() (string, error) { + var b [64]byte + if _, err := rand.Read(b[:]); err != nil { + return "", err + } + h := sha256.Sum256(b[:]) + return hex.EncodeToString(h[:16]), nil +} + +var _ net.Conn = (*meekConn)(nil) +var _ net.Addr = (*meekClientArgs)(nil) diff --git a/transports/transports.go b/transports/transports.go index e35673b..51a3f08 100644 --- a/transports/transports.go +++ b/transports/transports.go @@ -34,6 +34,7 @@ import ( "sync"

"git.torproject.org/pluggable-transports/obfs4.git/transports/base" + "git.torproject.org/pluggable-transports/obfs4.git/transports/meeklite" "git.torproject.org/pluggable-transports/obfs4.git/transports/obfs2" "git.torproject.org/pluggable-transports/obfs4.git/transports/obfs3" "git.torproject.org/pluggable-transports/obfs4.git/transports/obfs4" @@ -83,6 +84,7 @@ func Get(name string) base.Transport {

// Init initializes all of the integrated transports. func Init() error { + Register(new(meeklite.Transport)) Register(new(obfs2.Transport)) Register(new(obfs3.Transport)) Register(new(obfs4.Transport))