Merge release-20201109.0-56-g05d2a26f7 (automated)

1 files changed, 26 insertions, 3 deletions

diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 57976d4e3..835dcc54e 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -429,7 +429,13 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 	to := opts.To
 
 	e.mu.RLock()
-	defer e.mu.RUnlock()
+	lockReleased := false
+	defer func() {
+		if lockReleased {
+			return
+		}
+		e.mu.RUnlock()
+	}()
 
 	// If we've shutdown with SHUT_WR we are in an invalid state for sending.
 	if e.shutdownFlags&tcpip.ShutdownWrite != 0 {
@@ -475,7 +481,7 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 			if e.state != StateConnected {
 				err = tcpip.ErrInvalidEndpointState
 			}
-			return
+			return ch, err
 		}
 	} else {
 		// Reject destination address if it goes through a different
@@ -541,7 +547,24 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 		useDefaultTTL = false
 	}
 
-	if err := sendUDP(route, buffer.View(v).ToVectorisedView(), e.ID.LocalPort, dstPort, ttl, useDefaultTTL, e.sendTOS, e.owner, e.noChecksum); err != nil {
+	localPort := e.ID.LocalPort
+	sendTOS := e.sendTOS
+	owner := e.owner
+	noChecksum := e.noChecksum
+	lockReleased = true
+	e.mu.RUnlock()
+
+	// Do not hold lock when sending as loopback is synchronous and if the UDP
+	// datagram ends up generating an ICMP response then it can result in a
+	// deadlock where the ICMP response handling ends up acquiring this endpoint's
+	// mutex using e.mu.RLock() in endpoint.HandleControlPacket which can cause a
+	// deadlock if another caller is trying to acquire e.mu in exclusive mode w/
+	// e.mu.Lock(). Since e.mu.Lock() prevents any new read locks to ensure the
+	// lock can be eventually acquired.
+	//
+	// See: https://golang.org/pkg/sync/#RWMutex for details on why recursive read
+	// locking is prohibited.
+	if err := sendUDP(route, buffer.View(v).ToVectorisedView(), localPort, dstPort, ttl, useDefaultTTL, sendTOS, owner, noChecksum); err != nil {
 		return 0, nil, err
 	}
 	return int64(len(v)), nil, nil