Problem: Race condition in IPC sockets

Solution: Don't unlink file on close

File may not belong to the socket at that point.

.gitignore

@@ -47,6 +47,7 @@ test_last_endpoint
 test_pair_inproc
 test_pair_ipc
 test_pair_tcp
+test_rebind_ipc
 test_reqrep_inproc
 test_reqrep_ipc
 test_reqrep_tcp

Makefile.am

@@ -684,6 +684,7 @@ test_apps += \
 	tests/test_shutdown_stress \
 	tests/test_ipc_wildcard \
 	tests/test_pair_ipc \
+	tests/test_rebind_ipc \
 	tests/test_reqrep_ipc \
 	tests/test_use_fd_ipc \
 	tests/test_use_fd_tcp \
@@ -702,6 +703,9 @@ tests_test_pair_ipc_SOURCES = \
 	tests/testutil.hpp
 tests_test_pair_ipc_LDADD = src/libzmq.la
 
+tests_test_rebind_ipc_SOURCES = tests/test_rebind_ipc.cpp
+tests_test_rebind_ipc_LDADD = src/libzmq.la
+
 tests_test_reqrep_ipc_SOURCES = \
 	tests/test_reqrep_ipc.cpp \
 	tests/testutil.hpp

builds/gyp/project-tests.gypi

@@ -803,6 +803,17 @@
         'libzmq'
       ],
     },
+    {
+      'target_name': 'test_rebind_ipc',
+      'type': 'executable',
+      'sources': [
+        '../../tests/test_rebind_ipc.cpp',
+        '../../tests/testutil.hpp'
+      ],
+      'dependencies': [
+        'libzmq'
+      ],
+    },
     {
       'target_name': 'test_reqrep_ipc',
       'type': 'executable',

builds/gyp/project-tests.xml

@@ -72,6 +72,7 @@
     <test name = "test_udp" />
     <test name = "test_shutdown_stress" />
     <test name = "test_pair_ipc" />
+    <test name = "test_rebind_ipc" />
     <test name = "test_reqrep_ipc" />
     <test name = "test_use_fd_ipc" />
     <test name = "test_use_fd_tcp" />

src/ipc_listener.cpp

@@ -294,21 +294,12 @@ int zmq::ipc_listener_t::close ()
 
     s = retired_fd;
 
-    //  If there's an underlying UNIX domain socket, get rid of the file it
-    //  is associated with.
-    //  MUST NOT unlink if the FD is managed by the user, or it will stop
-    //  working after the first client connects. The user will take care of
-    //  cleaning up the file after the service is stopped.
     if (has_file && options.use_fd == -1) {
         rc = 0;
 
-        if ( !filename.empty () ) {
-          rc = ::unlink(filename.c_str ());
-        }
-
         if ( rc == 0 && !tmp_socket_dirname.empty() ) {
-          rc = ::rmdir(tmp_socket_dirname.c_str ());
-          tmp_socket_dirname.clear();
+            rc = ::rmdir(tmp_socket_dirname.c_str ());
+            tmp_socket_dirname.clear();
         }
 
         if (rc != 0) {

tests/CMakeLists.txt

@@ -80,6 +80,7 @@ if(NOT WIN32)
   list(APPEND tests
           test_ipc_wildcard
           test_pair_ipc
+          test_rebind_ipc
           test_reqrep_ipc
           test_proxy
           test_proxy_single_socket

tests/test_rebind_ipc.cpp

+/*
+    Copyright (c) 2007-2017 Contributors as noted in the AUTHORS file
+
+    This file is part of libzmq, the ZeroMQ core engine in C++.
+
+    libzmq is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    As a special exception, the Contributors give you permission to link
+    this library with independent modules to produce an executable,
+    regardless of the license terms of these independent modules, and to
+    copy and distribute the resulting executable under terms of your choice,
+    provided that you also meet, for each linked independent module, the
+    terms and conditions of the license of that module. An independent
+    module is a module which is not derived from or based on this library.
+    If you modify this library, you must extend this exception to your
+    version of the library.
+
+    libzmq is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "testutil.hpp"
+
+static const char* SOCKET_ADDR = "ipc:///tmp/tester";
+
+
+int main (void)
+{
+    setup_test_environment();
+
+    void *ctx = zmq_ctx_new ();
+    assert (ctx);
+
+    void *sb = zmq_socket (ctx, ZMQ_PUSH);
+    assert (sb);
+    int rc = zmq_bind (sb, SOCKET_ADDR);
+    assert (rc == 0);
+
+    void *sc = zmq_socket (ctx, ZMQ_PULL);
+    assert (sc);
+    rc = zmq_connect (sc, SOCKET_ADDR);
+    assert (rc == 0);
+
+    rc = zmq_send (sb, "42", 2, 0);
+    assert (rc == 2);
+
+    char buffer [2];
+    rc = zmq_recv(sc, buffer, 2, 0);
+    assert (rc == 2);
+
+    rc = zmq_close (sb);
+    assert (rc == 0);
+
+    sb = zmq_socket (ctx, ZMQ_PUSH);
+    assert (sb);
+    rc = zmq_bind (sb, SOCKET_ADDR);
+    assert (rc == 0);
+
+    rc = zmq_send (sb, "42", 2, 0);
+    assert (rc == 2);
+
+    rc = zmq_recv(sc, buffer, 2, 0);
+    assert (rc == 2);
+
+    rc = zmq_close (sc);
+    assert (rc == 0);
+
+    rc = zmq_close (sb);
+    assert (rc == 0);
+
+    rc = zmq_ctx_term (ctx);
+    assert (rc == 0);
+
+    return 0;
+}