Fix deadlock in UDP handleControlPacket path.

Fixing the sendto deadlock exposed yet another deadlock where a lock inversion
occurs on the handleControlPacket path where e.mu and demuxer.epsByNIC.mu are
acquired in reverse order from say when RegisterTransportEndpoint is called
in endpoint.Connect().

This fix sidesteps the issue by just making endpoint.state an atomic and gets rid
of the need to acquire e.mu in e.HandleControlPacket.

PiperOrigin-RevId: 344939895

1 files changed, 29 insertions, 2 deletions

diff --git a/test/syscalls/linux/udp_socket.cc b/test/syscalls/linux/udp_socket.cc
index 34255bfb8..90ef8bf21 100644
--- a/test/syscalls/linux/udp_socket.cc
+++ b/test/syscalls/linux/udp_socket.cc
@@ -375,8 +375,6 @@ TEST_P(UdpSocketTest, BindInUse) {
 }
 
 TEST_P(UdpSocketTest, ConnectWriteToInvalidPort) {
-  ASSERT_NO_ERRNO(BindLoopback());
-
   // Discover a free unused port by creating a new UDP socket, binding it
   // recording the just bound port and closing it. This is not guaranteed as it
   // can still race with other port UDP sockets trying to bind a port at the
@@ -410,6 +408,35 @@ TEST_P(UdpSocketTest, ConnectWriteToInvalidPort) {
   ASSERT_EQ(optlen, sizeof(err));
 }
 
+TEST_P(UdpSocketTest, ConnectSimultaneousWriteToInvalidPort) {
+  // Discover a free unused port by creating a new UDP socket, binding it
+  // recording the just bound port and closing it. This is not guaranteed as it
+  // can still race with other port UDP sockets trying to bind a port at the
+  // same time.
+  struct sockaddr_storage addr_storage = InetLoopbackAddr();
+  socklen_t addrlen = sizeof(addr_storage);
+  struct sockaddr* addr = reinterpret_cast<struct sockaddr*>(&addr_storage);
+  FileDescriptor s =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(GetFamily(), SOCK_DGRAM, IPPROTO_UDP));
+  ASSERT_THAT(bind(s.get(), addr, addrlen), SyscallSucceeds());
+  ASSERT_THAT(getsockname(s.get(), addr, &addrlen), SyscallSucceeds());
+  EXPECT_EQ(addrlen, addrlen_);
+  EXPECT_NE(*Port(&addr_storage), 0);
+  ASSERT_THAT(close(s.release()), SyscallSucceeds());
+
+  // Now connect to the port that we just released.
+  ScopedThread t([&] {
+    ASSERT_THAT(connect(sock_.get(), addr, addrlen_), SyscallSucceeds());
+  });
+
+  char buf[512];
+  RandomizeBuffer(buf, sizeof(buf));
+  // Send from sock_ to an unbound port.
+  ASSERT_THAT(sendto(sock_.get(), buf, sizeof(buf), 0, addr, addrlen_),
+              SyscallSucceedsWithValue(sizeof(buf)));
+  t.Join();
+}
+
 TEST_P(UdpSocketTest, ReceiveAfterConnect) {
   ASSERT_NO_ERRNO(BindLoopback());
   ASSERT_THAT(connect(sock_.get(), bind_addr_, addrlen_), SyscallSucceeds());