[tor-commits] [sandboxed-tor-browser/master] Bug #20780: Shuffle and persist the ordering of internal bridges.

[yawning at torproject.org]

commit f5183c21db683ac09da892bbb1c99797535de506
Author: Yawning Angel <yawning at schwanenlied.me>
Date:   Sat Dec 10 05:51:42 2016 +0000

    Bug #20780: Shuffle and persist the ordering of internal bridges.
    
    A new config entry `internalBridgeSeed` is added that holds a persistent
    seed used to permute the internal bridges at the point where the torrc
    is generated.
---
 ChangeLog                                          |  1 +
 src/cmd/sandboxed-tor-browser/internal/tor/tor.go  | 31 ++++++++++++++--------
 .../internal/ui/config/config.go                   | 13 +++++++++
 3 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 54d051b..6b30c61 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,5 @@
 Changes in version 0.0.2 - UNRELEASED:
+ * Bug #20780; Shuffle and persist the ordering of internal bridges.
 
 Changes in version 0.0.1 - 2016-12-09:
  * Initial release.
diff --git a/src/cmd/sandboxed-tor-browser/internal/tor/tor.go b/src/cmd/sandboxed-tor-browser/internal/tor/tor.go
index ecb53e3..e3dd047 100644
--- a/src/cmd/sandboxed-tor-browser/internal/tor/tor.go
+++ b/src/cmd/sandboxed-tor-browser/internal/tor/tor.go
@@ -25,7 +25,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
-	//	mrand "math/rand"
+	mrand "math/rand"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -444,17 +444,26 @@ func CfgToSandboxTorrc(cfg *config.Config, bridges map[string][]string) ([]byte,
 		}
 		bridgeArgs := []string{string(torrcBridges)}
 		if !cfg.Tor.UseCustomBridges {
-			// XXX: Actually shuffle this once there's a mechanism for
-			// persisting ordering. (#43)
-			for _, v := range bridges[cfg.Tor.InternalBridgeType] {
-				bridgeArgs = append(bridgeArgs, v)
-			}
-			/*
-				shuf := mrand.Perm(len(bridges[cfg.Tor.InternalBridgeType]))
-				for _, i := range shuf {
-					bridgeArgs = append(bridgeArgs, bridges[cfg.Tor.InternalBridgeType][i])
+			// No seed was set. Generate one with math.Rand, since this is
+			// purely for load balancing and doesn't require high grade
+			// entropy.
+			if cfg.Tor.InternalBridgeSeed == 0 {
+				seed := mrand.Int63()
+				cfg.Tor.SetInternalBridgeSeed(seed)
+				if err = cfg.Sync(); err != nil {
+					return nil, err
 				}
-			*/
+			}
+
+			// Initialize the deterministic random bit generator, using
+			// the persisted seed.
+			drbgSrc := mrand.NewSource(cfg.Tor.InternalBridgeSeed)
+			drbg := mrand.New(drbgSrc)
+
+			shuf := drbg.Perm(len(bridges[cfg.Tor.InternalBridgeType]))
+			for _, i := range shuf {
+				bridgeArgs = append(bridgeArgs, bridges[cfg.Tor.InternalBridgeType][i])
+			}
 		} else {
 			// The caller is responsible for making sure that this is indeed
 			// bridge lines, and not random other bullshit.
diff --git a/src/cmd/sandboxed-tor-browser/internal/ui/config/config.go b/src/cmd/sandboxed-tor-browser/internal/ui/config/config.go
index f119176..9295967 100644
--- a/src/cmd/sandboxed-tor-browser/internal/ui/config/config.go
+++ b/src/cmd/sandboxed-tor-browser/internal/ui/config/config.go
@@ -82,6 +82,10 @@ type Tor struct {
 	// bridges.
 	InternalBridgeType string `json:"internalBridgeType"`
 
+	// InternalBridgeSeed is the seed to use when permuting the internal
+	// bridges for load balancing purposes.
+	InternalBridgeSeed int64 `json:"internalBridgeSeed"`
+
 	// UseCustomBridges is if the user provided bridges should be used.
 	UseCustomBridges bool `json:"useCustomBridges"`
 
@@ -161,6 +165,15 @@ func (t *Tor) SetInternalBridgeType(s string) {
 	}
 }
 
+// SetInternalBridgeSeed sets the seed to use when permuting the internal
+// bridges for load balancing purposes and marks the config dirty.
+func (t *Tor) SetInternalBridgeSeed(i int64) {
+	if t.InternalBridgeSeed != i {
+		t.InternalBridgeSeed = i
+		t.cfg.isDirty = true
+	}
+}
+
 // SetCustomBridges sets the user provided custom bridge lines, and maarks the
 // config dirty.
 func (t *Tor) SetCustomBridges(s string) {