From d4febb45179fa99ee1d5783bcb693ed7ba14115c Mon Sep 17 00:00:00 2001 From: Damien Neil Date: Thu, 5 Feb 2026 15:56:13 -0800 Subject: [PATCH] crypto/tls: avoid data race when canceling a QUICConn's Context Methods on QUICConn are synchronous: The connection state is expected to change only in reaction to a user calling a QUICConn method, and the state change should finish completely before the method returns. The connection context provided to QUICConn.Start violates this model, because canceling the context causes an asynchronous state change. Prior to CL 719040, this caused no problems because canceling the context did not cause any user-visible state changes. In particular, canceling the context did not cause any new events to be immediately returned by QUICConn.NextEvent. CL 719040 introduced a new error event. Now, canceling a QUICConn's context causes a new connection event to be generated. Receiving this event causes a data race visible to the race detector, but the core problem is not the data race itself: It's that an asynchronous event (canceling the connection context) causes an change to the connection events. Fix this race by reworking the handling of QUICConn context cancellation a bit. We no longer react to cancellation while control of the connection lies with the user. We only process cancellation as part of a user call, such as QUICConn.Close or QUICConn.HandleData. Fixes #77274 Change-Id: If2e0f73618c4852114e0931b6bd0cb0b6a6a6964 Reviewed-on: https://go-review.googlesource.com/c/go/+/742561 LUCI-TryBot-Result: Go LUCI Auto-Submit: Damien Neil Reviewed-by: Roland Shoemaker --- src/crypto/tls/conn.go | 2 +- src/crypto/tls/quic.go | 21 +++++++++------------ src/crypto/tls/quic_test.go | 19 +++++++++++++++++++ 3 files changed, 29 insertions(+), 13 deletions(-) diff --git a/src/crypto/tls/conn.go b/src/crypto/tls/conn.go index a840125a45..9c662ef8f6 100644 --- a/src/crypto/tls/conn.go +++ b/src/crypto/tls/conn.go @@ -1531,7 +1531,7 @@ func (c *Conn) handshakeContext(ctx context.Context) (ret error) { defer cancel() if c.quic != nil { - c.quic.cancelc = handshakeCtx.Done() + c.quic.ctx = handshakeCtx c.quic.cancel = cancel } else if ctx.Done() != nil { // Close the connection if ctx is canceled before the function returns. diff --git a/src/crypto/tls/quic.go b/src/crypto/tls/quic.go index 76b7eb2cbd..c7d8508acb 100644 --- a/src/crypto/tls/quic.go +++ b/src/crypto/tls/quic.go @@ -162,7 +162,7 @@ type quicState struct { started bool signalc chan struct{} // handshake data is available to be read blockedc chan struct{} // handshake is waiting for data, closed when done - cancelc <-chan struct{} // handshake has been canceled + ctx context.Context // handshake context cancel context.CancelFunc waitingForDrain bool @@ -261,10 +261,11 @@ func (q *QUICConn) NextEvent() QUICEvent { // Close closes the connection and stops any in-progress handshake. func (q *QUICConn) Close() error { - if q.conn.quic.cancel == nil { + if q.conn.quic.ctx == nil { return nil // never started } q.conn.quic.cancel() + <-q.conn.quic.signalc for range q.conn.quic.blockedc { // Wait for the handshake goroutine to return. } @@ -511,20 +512,16 @@ func (c *Conn) quicWaitForSignal() error { // Send on blockedc to notify the QUICConn that the handshake is blocked. // Exported methods of QUICConn wait for the handshake to become blocked // before returning to the user. - select { - case c.quic.blockedc <- struct{}{}: - case <-c.quic.cancelc: - return c.sendAlertLocked(alertCloseNotify) - } + c.quic.blockedc <- struct{}{} // The QUICConn reads from signalc to notify us that the handshake may // be able to proceed. (The QUICConn reads, because we close signalc to // indicate that the handshake has completed.) - select { - case c.quic.signalc <- struct{}{}: - c.hand.Write(c.quic.readbuf) - c.quic.readbuf = nil - case <-c.quic.cancelc: + c.quic.signalc <- struct{}{} + if c.quic.ctx.Err() != nil { + // The connection has been canceled. return c.sendAlertLocked(alertCloseNotify) } + c.hand.Write(c.quic.readbuf) + c.quic.readbuf = nil return nil } diff --git a/src/crypto/tls/quic_test.go b/src/crypto/tls/quic_test.go index bd0eaa4d47..0cf8b337e1 100644 --- a/src/crypto/tls/quic_test.go +++ b/src/crypto/tls/quic_test.go @@ -11,6 +11,7 @@ import ( "fmt" "reflect" "strings" + "sync" "testing" ) @@ -480,6 +481,24 @@ func TestQUICStartContextPropagation(t *testing.T) { } } +func TestQUICContextCancelation(t *testing.T) { + ctx, cancel := context.WithCancel(context.Background()) + config := &QUICConfig{TLSConfig: testConfig.Clone()} + config.TLSConfig.MinVersion = VersionTLS13 + cli := newTestQUICClient(t, config) + cli.conn.SetTransportParameters(nil) + srv := newTestQUICServer(t, config) + srv.conn.SetTransportParameters(nil) + // Verify that canceling the connection context concurrently does not cause any races. + // See https://go.dev/issue/77274. + var wg sync.WaitGroup + wg.Go(func() { + _ = runTestQUICConnection(ctx, cli, srv, nil) + }) + wg.Go(cancel) + wg.Wait() +} + func TestQUICDelayedTransportParameters(t *testing.T) { clientConfig := &QUICConfig{TLSConfig: testConfig.Clone()} clientConfig.TLSConfig.MinVersion = VersionTLS13 -- 2.52.0