Fix race problem with detecting listening inetd sockets

The previous detection would fail if the socket closed before we
had time to inspect it, which got us stuck in a loop as we would
try (and fail) to do accept() on a non-listening socket.

3 files changed, 9 insertions, 15 deletions

diff --git a/common/network/TcpSocket.cxx b/common/network/TcpSocket.cxx
index 6561f3d6..cf03c10d 100644
--- a/common/network/TcpSocket.cxx
+++ b/common/network/TcpSocket.cxx
@@ -360,18 +360,14 @@ bool TcpSocket::cork(int sock, bool enable) {
 #endif
 }
 
-bool TcpSocket::isSocket(int sock)
+bool TcpSocket::isListening(int sock)
 {
-  vnc_sockaddr_t sa;
-  socklen_t sa_size = sizeof(sa);
-  return getsockname(sock, &sa.u.sa, &sa_size) >= 0;
-}
-
-bool TcpSocket::isConnected(int sock)
-{
-  vnc_sockaddr_t sa;
-  socklen_t sa_size = sizeof(sa);
-  return getpeername(sock, &sa.u.sa, &sa_size) >= 0;
+  int listening = 0;
+  socklen_t listening_size = sizeof(listening);
+  if (getsockopt(sock, SOL_SOCKET, SO_ACCEPTCONN,
+                 (char *)&listening, &listening_size) < 0)
+    return false;
+  return listening != 0;
 }
 
 int TcpSocket::getSockPort(int sock)
diff --git a/common/network/TcpSocket.h b/common/network/TcpSocket.h
index 02f04c91..a97e6839 100644
--- a/common/network/TcpSocket.h
+++ b/common/network/TcpSocket.h
@@ -65,8 +65,7 @@ namespace network {
 
     static bool enableNagles(int sock, bool enable);
     static bool cork(int sock, bool enable);
-    static bool isSocket(int sock);
-    static bool isConnected(int sock);
+    static bool isListening(int sock);
     static int getSockPort(int sock);
   private:
     bool closeFd;
diff --git a/unix/xserver/hw/vnc/vncExtInit.cc b/unix/xserver/hw/vnc/vncExtInit.cc
index 2d918b04..863cd36b 100644
--- a/unix/xserver/hw/vnc/vncExtInit.cc
+++ b/unix/xserver/hw/vnc/vncExtInit.cc
@@ -137,8 +137,7 @@ void vncExtensionInit(void)
         std::list<network::TcpListener*> listeners;
         std::list<network::TcpListener*> httpListeners;
         if (scr == 0 && vncInetdSock != -1) {
-          if (network::TcpSocket::isSocket(vncInetdSock) &&
-              !network::TcpSocket::isConnected(vncInetdSock))
+          if (network::TcpSocket::isListening(vncInetdSock))
           {
             listeners.push_back(new network::TcpListener(vncInetdSock));
             vlog.info("inetd wait");