Cygwin: fix memory corruption/SEGV if certain socket functions fail

Regression introduced with 2.11.0:

The failure paths in socket, socketpair and accept4 functions and
methods accidentally release *unused* cygheap_fdmanip objects.  The
subsequently called dtable::release method was designed to be called for
*used* cygheap_fdmanip objects only.  Using them on unused objects leads
to NULL pointer member dereferencing.

Worse, the inet/local accept4 methods only release the cygheap_fdmanip
object but neglect to delete the just created fhandler_socket_* object.

Fix this by removing the erroneous release calls in the aforementioned
failure paths and delete the fhandler_socket_* object in accept4 instead.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/fhandler_socket_inet.cc

@@ -898,7 +898,7 @@ fhandler_socket_inet::accept4 (struct sockaddr *peer, int *len, int flags)
 		}
 	    }
 	  else
-	    fd.release ();
+	    delete sock;
 	}
       if (ret == -1)
 	::closesocket (res);

winsup/cygwin/fhandler_socket_local.cc

@@ -988,7 +988,6 @@ fhandler_socket_local::accept4 (struct sockaddr *peer, int *len, int flags)
 		  ret = sock->af_local_accept ();
 		  if (ret == -1)
 		    {
-		      fd.release ();
 		      delete sock;
 		      set_winsock_errno ();
 		      return -1;
@@ -1013,7 +1012,7 @@ fhandler_socket_local::accept4 (struct sockaddr *peer, int *len, int flags)
 		}
 	    }
 	  else
-	    fd.release ();
+	    delete sock;
 	}
       if (ret == -1)
 	::closesocket (res);

winsup/cygwin/fhandler_socket_unix.cc

@@ -1639,7 +1639,6 @@ fhandler_socket_unix::accept4 (struct sockaddr *peer, int *len, int flags)
 create_shmem_failed:
 		  delete sock;
 		}
-	      fd.release ();
 	    }
 	}
       /* Ouch!  We can't handle the client if we couldn't

winsup/cygwin/net.cc

@@ -536,10 +536,7 @@ cygwin_socket (int af, int type, int protocol)
 	  res = fd;
 	}
       else
-	{
-	  delete fh;
-	  fd.release ();
-	}
+	delete fh;
     }
 
 done:
@@ -2314,10 +2311,7 @@ socketpair (int af, int type, int protocol, int sv[2])
 
       cygheap_fdnew fd_out (fd_in, false);
       if (fd_out < 0)
-	{
-	  fd_in.release ();
-	  goto done;
-	}
+	goto done;
 
       fh_in = reinterpret_cast<fhandler_socket *> (build_fh_dev (*dev));
       fh_out = reinterpret_cast<fhandler_socket *> (build_fh_dev (*dev));
@@ -2343,8 +2337,6 @@ socketpair (int af, int type, int protocol, int sv[2])
 	{
 	  delete fh_in;
 	  delete fh_out;
-	  fd_in.release ();
-	  fd_out.release ();
 	}
     }
 

winsup/cygwin/release/2.11.2

@@ -14,3 +14,7 @@ Bug Fixes
 
 - Fix a memory corruption when using pipes or FIFOs
   Addresses: https://cygwin.com/ml/cygwin-patches/2018-q4/msg00000.html
+
+- Fix potential memory corruption and SEGV if socket(2), socketpair(2),
+  accept(2), or accept4(2) fail.
+  Addresses: https://cygwin.com/ml/cygwin/2018-10/msg00229.html