commit e3351cb08abe6b806fa018bc8915f0f5ae045a40 Author: Cecylia Bocovich cohosh@torproject.org Date: Mon Jun 21 15:39:41 2021 -0400

Fix data race for Peers.collection

We used a WaitGroup to prevent a call to Peers.End from melting snowflakes while a new one is being collected. However, calls to WaitGroup.Add are in a race with WaitGroup.Wait. To fix this, we use a Mutex instead. --- client/lib/peers.go | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/client/lib/peers.go b/client/lib/peers.go index 66373f1..7fba572 100644 --- a/client/lib/peers.go +++ b/client/lib/peers.go @@ -28,7 +28,7 @@ type Peers struct {

melt chan struct{}

- collection sync.WaitGroup + collectLock sync.Mutex }

// Construct a fresh container of remote peers. @@ -48,8 +48,8 @@ func NewPeers(tongue Tongue) (*Peers, error) { // As part of |SnowflakeCollector| interface. func (p *Peers) Collect() (*WebRTCPeer, error) { // Engage the Snowflake Catching interface, which must be available. - p.collection.Add(1) - defer p.collection.Done() + p.collectLock.Lock() + defer p.collectLock.Unlock() select { case <-p.melt: return nil, fmt.Errorf("Snowflakes have melted") @@ -121,7 +121,8 @@ func (p *Peers) purgeClosedPeers() { // Close all Peers contained here. func (p *Peers) End() { close(p.melt) - p.collection.Wait() + p.collectLock.Lock() + defer p.collectLock.Unlock() close(p.snowflakeChan) cnt := p.Count() for e := p.activePeers.Front(); e != nil; {