char: fix use-after-free with dup chardev & reconnect

With a reconnect socket, qemu_char_open() will start a background
thread. It should keep a reference on the chardev.

Fixes invalid read:
READ of size 8 at 0x6040000ac858 thread T7
    #0 0x5555598d37b8 in unix_connect_saddr /home/elmarco/src/qq/util/qemu-sockets.c:954
    avatartwo#1 0x5555598d4751 in socket_connect /home/elmarco/src/qq/util/qemu-sockets.c:1109
    avatartwo#2 0x555559707c34 in qio_channel_socket_connect_sync /home/elmarco/src/qq/io/channel-socket.c:145
    avatartwo#3 0x5555596adebb in tcp_chr_connect_client_task /home/elmarco/src/qq/chardev/char-socket.c:1104
    avatartwo#4 0x555559723d55 in qio_task_thread_worker /home/elmarco/src/qq/io/task.c:123
    avatartwo#5 0x5555598a6731 in qemu_thread_start /home/elmarco/src/qq/util/qemu-thread-posix.c:519
    avatartwo#6 0x7ffff40d4431 in start_thread (/lib64/libpthread.so.0+0x9431)
    avatartwo#7 0x7ffff40029d2 in __clone (/lib64/libc.so.6+0x1019d2)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200420112012.567284-1-marcandre.lureau@redhat.com>

chardev/char-socket.c

@@ -1129,7 +1129,8 @@ static void tcp_chr_connect_client_async(Chardev *chr)
      */
     s->connect_task = qio_task_new(OBJECT(sioc),
                                    qemu_chr_socket_connected,
-                                   chr, NULL);
+                                   object_ref(OBJECT(chr)),
+                                   (GDestroyNotify)object_unref);
     qio_task_run_in_thread(s->connect_task,
                            tcp_chr_connect_client_task,
                            s->addr,

tests/test-char.c

@@ -904,6 +904,52 @@ typedef struct {
     char_socket_cb event_cb;
 } CharSocketClientTestConfig;
 
+static void char_socket_client_dupid_test(gconstpointer opaque)
+{
+    const CharSocketClientTestConfig *config = opaque;
+    QIOChannelSocket *ioc;
+    char *optstr;
+    Chardev *chr1, *chr2;
+    SocketAddress *addr;
+    QemuOpts *opts;
+    Error *local_err = NULL;
+
+    /*
+     * Setup a listener socket and determine get its address
+     * so we know the TCP port for the client later
+     */
+    ioc = qio_channel_socket_new();
+    g_assert_nonnull(ioc);
+    qio_channel_socket_listen_sync(ioc, config->addr, 1, &error_abort);
+    addr = qio_channel_socket_get_local_address(ioc, &error_abort);
+    g_assert_nonnull(addr);
+
+    /*
+     * Populate the chardev address based on what the server
+     * is actually listening on
+     */
+    optstr = char_socket_addr_to_opt_str(addr,
+                                         config->fd_pass,
+                                         config->reconnect,
+                                         false);
+
+    opts = qemu_opts_parse_noisily(qemu_find_opts("chardev"),
+                                   optstr, true);
+    g_assert_nonnull(opts);
+    chr1 = qemu_chr_new_from_opts(opts, NULL, &error_abort);
+    g_assert_nonnull(chr1);
+
+    chr2 = qemu_chr_new_from_opts(opts, NULL, &local_err);
+    g_assert_null(chr2);
+    error_free_or_abort(&local_err);
+
+    object_unref(OBJECT(ioc));
+    qemu_opts_del(opts);
+    object_unparent(OBJECT(chr1));
+    qapi_free_SocketAddress(addr);
+    g_free(optstr);
+}
+
 static void char_socket_client_test(gconstpointer opaque)
 {
     const CharSocketClientTestConfig *config = opaque;
@@ -1456,7 +1502,7 @@ int main(int argc, char **argv)
 
 #define SOCKET_CLIENT_TEST(name, addr)                                  \
     static CharSocketClientTestConfig client1 ## name =                 \
-        { addr, NULL, false, false, char_socket_event};                 \
+        { addr, NULL, false, false, char_socket_event };                \
     static CharSocketClientTestConfig client2 ## name =                 \
         { addr, NULL, true, false, char_socket_event };                 \
     static CharSocketClientTestConfig client3 ## name =                 \
@@ -1470,6 +1516,8 @@ int main(int argc, char **argv)
     static CharSocketClientTestConfig client7 ## name =                 \
         { addr, ",reconnect=1", true, false,                            \
             char_socket_event_with_error };                             \
+    static CharSocketClientTestConfig client8 ## name =                 \
+        { addr, ",reconnect=1", false, false, char_socket_event };      \
     g_test_add_data_func("/char/socket/client/mainloop/" # name,        \
                          &client1 ##name, char_socket_client_test);     \
     g_test_add_data_func("/char/socket/client/wait-conn/" # name,       \
@@ -1483,7 +1531,9 @@ int main(int argc, char **argv)
     g_test_add_data_func("/char/socket/client/wait-conn-fdpass/" # name, \
                          &client6 ##name, char_socket_client_test);     \
     g_test_add_data_func("/char/socket/client/reconnect-error/" # name, \
-                         &client7 ##name, char_socket_client_test)
+                         &client7 ##name, char_socket_client_test);     \
+    g_test_add_data_func("/char/socket/client/dupid-reconnect/" # name, \
+                         &client8 ##name, char_socket_client_dupid_test)
 
     if (has_ipv4) {
         SOCKET_SERVER_TEST(tcp, &tcpaddr);