Merge branch 'backport-1902-spawn-path-fix-glib-2-66' into 'glib-2-66'

Backport !1902 “spawn: Don't set a search path if we don't want to search PATH” to glib-2-66

See merge request GNOME/glib!1913

7 files changed, 707 insertions, 10 deletions

diff --git a/glib/gspawn.c b/glib/gspawn.c
index c37ac7c84..c8e0ca806 100644
--- a/glib/gspawn.c
+++ b/glib/gspawn.c
@@ -1753,8 +1753,10 @@ fork_exec_with_fds (gboolean              intermediate_child,
   gint status;
   const gchar *chosen_search_path;
   gchar *search_path_buffer = NULL;
+  gchar *search_path_buffer_heap = NULL;
   gsize search_path_buffer_len = 0;
   gchar **argv_buffer = NULL;
+  gchar **argv_buffer_heap = NULL;
   gsize argv_buffer_len = 0;
 
 #ifdef POSIX_SPAWN_AVAILABLE
@@ -1819,7 +1821,7 @@ fork_exec_with_fds (gboolean              intermediate_child,
   if (search_path && chosen_search_path == NULL)
     chosen_search_path = g_getenv ("PATH");
 
-  if (chosen_search_path == NULL)
+  if ((search_path || search_path_from_envp) && chosen_search_path == NULL)
     {
       /* There is no 'PATH' in the environment.  The default
        * * search path in libc is the current directory followed by
@@ -1834,25 +1836,58 @@ fork_exec_with_fds (gboolean              intermediate_child,
       chosen_search_path = "/bin:/usr/bin:.";
     }
 
+  if (search_path || search_path_from_envp)
+    g_assert (chosen_search_path != NULL);
+  else
+    g_assert (chosen_search_path == NULL);
+
   /* Allocate a buffer which the fork()ed child can use to assemble potential
    * paths for the binary to exec(), combining the argv[0] and elements from
    * the chosen_search_path. This can’t be done in the child because malloc()
    * (or alloca()) are not async-signal-safe (see `man 7 signal-safety`).
    *
    * Add 2 for the nul terminator and a leading `/`. */
-  search_path_buffer_len = strlen (chosen_search_path) + strlen (argv[0]) + 2;
-  search_path_buffer = g_malloc (search_path_buffer_len);
+  if (chosen_search_path != NULL)
+    {
+      search_path_buffer_len = strlen (chosen_search_path) + strlen (argv[0]) + 2;
+      if (search_path_buffer_len < 4000)
+        {
+          /* Prefer small stack allocations to avoid valgrind leak warnings
+           * in forked child. The 4000B cutoff is arbitrary. */
+          search_path_buffer = g_alloca (search_path_buffer_len);
+        }
+      else
+        {
+          search_path_buffer_heap = g_malloc (search_path_buffer_len);
+          search_path_buffer = search_path_buffer_heap;
+        }
+    }
+
+  if (search_path || search_path_from_envp)
+    g_assert (search_path_buffer != NULL);
+  else
+    g_assert (search_path_buffer == NULL);
 
   /* And allocate a buffer which is 2 elements longer than @argv, so that if
    * script_execute() has to be called later on, it can build a wrapper argv
    * array in this buffer. */
   argv_buffer_len = g_strv_length (argv) + 2;
-  argv_buffer = g_new (gchar *, argv_buffer_len);
+  if (argv_buffer_len < 4000 / sizeof (gchar *))
+    {
+      /* Prefer small stack allocations to avoid valgrind leak warnings
+       * in forked child. The 4000B cutoff is arbitrary. */
+      argv_buffer = g_newa (gchar *, argv_buffer_len);
+    }
+  else
+    {
+      argv_buffer_heap = g_new (gchar *, argv_buffer_len);
+      argv_buffer = argv_buffer_heap;
+    }
 
   if (!g_unix_open_pipe (child_err_report_pipe, pipe_flags, error))
     {
-      g_free (search_path_buffer);
-      g_free (argv_buffer);
+      g_free (search_path_buffer_heap);
+      g_free (argv_buffer_heap);
       return FALSE;
     }
 
@@ -2099,8 +2134,8 @@ fork_exec_with_fds (gboolean              intermediate_child,
       close_and_invalidate (&child_err_report_pipe[0]);
       close_and_invalidate (&child_pid_report_pipe[0]);
 
-      g_free (search_path_buffer);
-      g_free (argv_buffer);
+      g_free (search_path_buffer_heap);
+      g_free (argv_buffer_heap);
 
       if (child_pid)
         *child_pid = pid;
@@ -2134,8 +2169,8 @@ fork_exec_with_fds (gboolean              intermediate_child,
   close_and_invalidate (&child_pid_report_pipe[0]);
   close_and_invalidate (&child_pid_report_pipe[1]);
 
-  g_free (search_path_buffer);
-  g_free (argv_buffer);
+  g_free (search_path_buffer_heap);
+  g_free (argv_buffer_heap);
 
   return FALSE;
 }
diff --git a/glib/tests/meson.build b/glib/tests/meson.build
index 6eb23e8a7..d35bd16fd 100644
--- a/glib/tests/meson.build
+++ b/glib/tests/meson.build
@@ -89,6 +89,7 @@ glib_tests = {
   'slist' : {},
   'sort' : {},
   'spawn-multithreaded' : {},
+  'spawn-path-search' : {},
   'spawn-singlethread' : {},
   'strfuncs' : {},
   'string' : {},
@@ -235,6 +236,20 @@ foreach test_name, extra_args : glib_tests
   test(test_name, exe, env : test_env, timeout : timeout, suite : suite)
 endforeach
 
+executable('spawn-path-search-helper', 'spawn-path-search-helper.c',
+  c_args : test_cargs,
+  dependencies : test_deps,
+  install_dir: installed_tests_execdir,
+  install: installed_tests_enabled,
+)
+
+executable('spawn-test-helper', 'spawn-test-helper.c',
+  c_args : test_cargs,
+  dependencies : test_deps,
+  install_dir: installed_tests_execdir,
+  install: installed_tests_enabled,
+)
+
 # test-spawn-echo helper binary required by the spawn tests above
 executable('test-spawn-echo', 'test-spawn-echo.c',
   c_args : test_cargs,
@@ -266,3 +281,5 @@ if not meson.is_cross_build() and host_system != 'windows'
     )
   endif
 endif
+
+subdir('path-test-subdir')
diff --git a/glib/tests/path-test-subdir/meson.build b/glib/tests/path-test-subdir/meson.build
new file mode 100644
index 000000000..351254cd8
--- /dev/null
+++ b/glib/tests/path-test-subdir/meson.build
@@ -0,0 +1,6 @@
+executable('spawn-test-helper', 'spawn-test-helper.c',
+  c_args : test_cargs,
+  dependencies : test_deps,
+  install_dir: join_paths(installed_tests_execdir, 'path-test-subdir'),
+  install: installed_tests_enabled,
+)
diff --git a/glib/tests/path-test-subdir/spawn-test-helper.c b/glib/tests/path-test-subdir/spawn-test-helper.c
new file mode 100644
index 000000000..f9f2cee84
--- /dev/null
+++ b/glib/tests/path-test-subdir/spawn-test-helper.c
@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int main (void)
+{
+  fprintf (stderr, "this is spawn-test-helper from path-test-subdir\n");
+  return 5;
+}
diff --git a/glib/tests/spawn-path-search-helper.c b/glib/tests/spawn-path-search-helper.c
new file mode 100644
index 000000000..378c203c7
--- /dev/null
+++ b/glib/tests/spawn-path-search-helper.c
@@ -0,0 +1,171 @@
+/*
+ * Copyright 2021 Collabora Ltd.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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 library; if not, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+#include <errno.h>
+#include <stdio.h>
+
+#include <glib.h>
+
+#ifdef G_OS_UNIX
+#include <sys/types.h>
+#include <sys/wait.h>
+#endif
+
+static void
+child_setup (gpointer user_data)
+{
+}
+
+typedef struct
+{
+  int wait_status;
+  gboolean done;
+} ChildStatus;
+
+static ChildStatus child_status = { -1, FALSE };
+
+static void
+child_watch_cb (GPid pid,
+                gint status,
+                gpointer user_data)
+{
+  child_status.wait_status = status;
+  child_status.done = TRUE;
+}
+
+int
+main (int    argc,
+      char **argv)
+{
+  gboolean search_path = FALSE;
+  gboolean search_path_from_envp = FALSE;
+  gboolean slow_path = FALSE;
+  gboolean unset_path_in_envp = FALSE;
+  gchar *chdir_child = NULL;
+  gchar *set_path_in_envp = NULL;
+  gchar **envp = NULL;
+  GOptionEntry entries[] =
+  {
+    { "chdir-child", '\0',
+      G_OPTION_FLAG_NONE, G_OPTION_ARG_FILENAME, &chdir_child,
+      "Run PROGRAM in this working directory", NULL },
+    { "search-path", '\0',
+      G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &search_path,
+      "Search PATH for PROGRAM", NULL },
+    { "search-path-from-envp", '\0',
+      G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &search_path_from_envp,
+      "Search PATH from specified environment", NULL },
+    { "set-path-in-envp", '\0',
+      G_OPTION_FLAG_NONE, G_OPTION_ARG_FILENAME, &set_path_in_envp,
+      "Set PATH in specified environment to this value", "PATH", },
+    { "unset-path-in-envp", '\0',
+      G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &unset_path_in_envp,
+      "Unset PATH in specified environment", NULL },
+    { "slow-path", '\0',
+      G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &slow_path,
+      "Use a child-setup function to avoid the posix_spawn fast path", NULL },
+    { NULL }
+  };
+  GError *error = NULL;
+  int ret = 1;
+  GSpawnFlags spawn_flags = G_SPAWN_DO_NOT_REAP_CHILD;
+  GPid pid;
+  GOptionContext *context = NULL;
+
+  context = g_option_context_new ("PROGRAM [ARGS...]");
+  g_option_context_add_main_entries (context, entries, NULL);
+
+  if (!g_option_context_parse (context, &argc, &argv, &error))
+    {
+      ret = 2;
+      goto out;
+    }
+
+  if (argc < 2)
+    {
+      g_set_error (&error, G_OPTION_ERROR, G_OPTION_ERROR_FAILED,
+                   "Usage: %s [OPTIONS] PROGRAM [ARGS...]", argv[0]);
+      ret = 2;
+      goto out;
+    }
+
+  envp = g_get_environ ();
+
+  if (set_path_in_envp != NULL && unset_path_in_envp)
+    {
+      g_set_error (&error, G_OPTION_ERROR, G_OPTION_ERROR_FAILED,
+                   "Cannot both set PATH and unset it");
+      ret = 2;
+      goto out;
+    }
+
+  if (set_path_in_envp != NULL)
+    envp = g_environ_setenv (envp, "PATH", set_path_in_envp, TRUE);
+
+  if (unset_path_in_envp)
+    envp = g_environ_unsetenv (envp, "PATH");
+
+  if (search_path)
+    spawn_flags |= G_SPAWN_SEARCH_PATH;
+
+  if (search_path_from_envp)
+    spawn_flags |= G_SPAWN_SEARCH_PATH_FROM_ENVP;
+
+  if (!g_spawn_async_with_pipes (chdir_child,
+                                 &argv[1],
+                                 envp,
+                                 spawn_flags,
+                                 slow_path ? child_setup : NULL,
+                                 NULL,  /* user_data */
+                                 &pid,
+                                 NULL,  /* stdin */
+                                 NULL,  /* stdout */
+                                 NULL,  /* stderr */
+                                 &error))
+    {
+      ret = 1;
+      goto out;
+    }
+
+  g_child_watch_add (pid, child_watch_cb, NULL);
+
+  while (!child_status.done)
+    g_main_context_iteration (NULL, TRUE);
+
+  g_spawn_close_pid (pid);
+
+#ifdef G_OS_UNIX
+  if (WIFEXITED (child_status.wait_status))
+    ret = WEXITSTATUS (child_status.wait_status);
+  else
+    ret = 1;
+#else
+  ret = child_status.wait_status;
+#endif
+
+out:
+  if (error != NULL)
+    fprintf (stderr, "%s\n", error->message);
+
+  g_free (set_path_in_envp);
+  g_free (chdir_child);
+  g_clear_error (&error);
+  g_strfreev (envp);
+  g_option_context_free (context);
+  return ret;
+}
diff --git a/glib/tests/spawn-path-search.c b/glib/tests/spawn-path-search.c
new file mode 100644
index 000000000..f4278f3e0
--- /dev/null
+++ b/glib/tests/spawn-path-search.c
@@ -0,0 +1,454 @@
+/*
+ * Copyright 2021 Collabora Ltd.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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 library; if not, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+#include <glib.h>
+
+#ifdef G_OS_UNIX
+#include <sys/types.h>
+#include <sys/wait.h>
+#endif
+
+static void
+test_do_not_search (void)
+{
+  GPtrArray *argv = g_ptr_array_new_with_free_func (g_free);
+  gchar *here = g_test_build_filename (G_TEST_BUILT, ".", NULL);
+  gchar *subdir = g_test_build_filename (G_TEST_BUILT, "path-test-subdir", NULL);
+  gchar **envp = g_get_environ ();
+  gchar *out = NULL;
+  gchar *err = NULL;
+  GError *error = NULL;
+  int wait_status = -1;
+
+  g_test_summary ("Without G_SPAWN_SEARCH_PATH, spawn-test-helper "
+                  "means ./spawn-test-helper.");
+
+  envp = g_environ_setenv (envp, "PATH", subdir, TRUE);
+
+  g_ptr_array_add (argv,
+                   g_test_build_filename (G_TEST_BUILT, "spawn-path-search-helper", NULL));
+  g_ptr_array_add (argv, g_strdup ("--"));
+  g_ptr_array_add (argv, g_strdup ("spawn-test-helper"));
+  g_ptr_array_add (argv, NULL);
+
+  g_spawn_sync (here,
+                (char **) argv->pdata,
+                envp,
+                G_SPAWN_DEFAULT,
+                NULL,  /* child setup */
+                NULL,  /* user data */
+                &out,
+                &err,
+                &wait_status,
+                &error);
+  g_assert_no_error (error);
+
+  g_test_message ("%s", out);
+  g_test_message ("%s", err);
+  g_assert_nonnull (strstr (err, "this is spawn-test-helper from glib/tests"));
+
+#ifdef G_OS_UNIX
+  g_assert_true (WIFEXITED (wait_status));
+  g_assert_cmpint (WEXITSTATUS (wait_status), ==, 0);
+#endif
+
+  g_strfreev (envp);
+  g_free (here);
+  g_free (subdir);
+  g_free (out);
+  g_free (err);
+  g_ptr_array_unref (argv);
+}
+
+static void
+test_search_path (void)
+{
+  GPtrArray *argv = g_ptr_array_new_with_free_func (g_free);
+  gchar *here = g_test_build_filename (G_TEST_BUILT, ".", NULL);
+  gchar *subdir = g_test_build_filename (G_TEST_BUILT, "path-test-subdir", NULL);
+  gchar **envp = g_get_environ ();
+  gchar *out = NULL;
+  gchar *err = NULL;
+  GError *error = NULL;
+  int wait_status = -1;
+
+  g_test_summary ("With G_SPAWN_SEARCH_PATH, spawn-test-helper "
+                  "means $PATH/spawn-test-helper.");
+
+  envp = g_environ_setenv (envp, "PATH", subdir, TRUE);
+
+  g_ptr_array_add (argv,
+                   g_test_build_filename (G_TEST_BUILT, "spawn-path-search-helper", NULL));
+  g_ptr_array_add (argv, g_strdup ("--search-path"));
+  g_ptr_array_add (argv, g_strdup ("--"));
+  g_ptr_array_add (argv, g_strdup ("spawn-test-helper"));
+  g_ptr_array_add (argv, NULL);
+
+  g_spawn_sync (here,
+                (char **) argv->pdata,
+                envp,
+                G_SPAWN_DEFAULT,
+                NULL,  /* child setup */
+                NULL,  /* user data */
+                &out,
+                &err,
+                &wait_status,
+                &error);
+  g_assert_no_error (error);
+
+  g_test_message ("%s", out);
+  g_test_message ("%s", err);
+  g_assert_nonnull (strstr (err, "this is spawn-test-helper from path-test-subdir"));
+
+#ifdef G_OS_UNIX
+  g_assert_true (WIFEXITED (wait_status));
+  g_assert_cmpint (WEXITSTATUS (wait_status), ==, 5);
+#endif
+
+  g_strfreev (envp);
+  g_free (here);
+  g_free (subdir);
+  g_free (out);
+  g_free (err);
+  g_ptr_array_unref (argv);
+}
+
+static void
+test_search_path_from_envp (void)
+{
+  GPtrArray *argv = g_ptr_array_new_with_free_func (g_free);
+  gchar *here = g_test_build_filename (G_TEST_BUILT, ".", NULL);
+  gchar *subdir = g_test_build_filename (G_TEST_BUILT, "path-test-subdir", NULL);
+  gchar **envp = g_get_environ ();
+  gchar *out = NULL;
+  gchar *err = NULL;
+  GError *error = NULL;
+  int wait_status = -1;
+
+  g_test_summary ("With G_SPAWN_SEARCH_PATH_FROM_ENVP, spawn-test-helper "
+                  "means $PATH/spawn-test-helper with $PATH from envp.");
+
+  envp = g_environ_setenv (envp, "PATH", here, TRUE);
+
+  g_ptr_array_add (argv,
+                   g_test_build_filename (G_TEST_BUILT, "spawn-path-search-helper", NULL));
+  g_ptr_array_add (argv, g_strdup ("--search-path-from-envp"));
+  g_ptr_array_add (argv, g_strdup ("--set-path-in-envp"));
+  g_ptr_array_add (argv, g_strdup (subdir));
+  g_ptr_array_add (argv, g_strdup ("--"));
+  g_ptr_array_add (argv, g_strdup ("spawn-test-helper"));
+  g_ptr_array_add (argv, NULL);
+
+  g_spawn_sync (here,
+                (char **) argv->pdata,
+                envp,
+                G_SPAWN_DEFAULT,
+                NULL,  /* child setup */
+                NULL,  /* user data */
+                &out,
+                &err,
+                &wait_status,
+                &error);
+  g_assert_no_error (error);
+
+  g_test_message ("%s", out);
+  g_test_message ("%s", err);
+  g_assert_nonnull (strstr (err, "this is spawn-test-helper from path-test-subdir"));
+
+#ifdef G_OS_UNIX
+  g_assert_true (WIFEXITED (wait_status));
+  g_assert_cmpint (WEXITSTATUS (wait_status), ==, 5);
+#endif
+
+  g_strfreev (envp);
+  g_free (here);
+  g_free (subdir);
+  g_free (out);
+  g_free (err);
+  g_ptr_array_unref (argv);
+}
+
+static void
+test_search_path_ambiguous (void)
+{
+  GPtrArray *argv = g_ptr_array_new_with_free_func (g_free);
+  gchar *here = g_test_build_filename (G_TEST_BUILT, ".", NULL);
+  gchar *subdir = g_test_build_filename (G_TEST_BUILT, "path-test-subdir", NULL);
+  gchar **envp = g_get_environ ();
+  gchar *out = NULL;
+  gchar *err = NULL;
+  GError *error = NULL;
+  int wait_status = -1;
+
+  g_test_summary ("With G_SPAWN_SEARCH_PATH and G_SPAWN_SEARCH_PATH_FROM_ENVP, "
+                  "the latter wins.");
+
+  envp = g_environ_setenv (envp, "PATH", here, TRUE);
+
+  g_ptr_array_add (argv,
+                   g_test_build_filename (G_TEST_BUILT, "spawn-path-search-helper", NULL));
+  g_ptr_array_add (argv, g_strdup ("--search-path"));
+  g_ptr_array_add (argv, g_strdup ("--search-path-from-envp"));
+  g_ptr_array_add (argv, g_strdup ("--set-path-in-envp"));
+  g_ptr_array_add (argv, g_strdup (subdir));
+  g_ptr_array_add (argv, g_strdup ("--"));
+  g_ptr_array_add (argv, g_strdup ("spawn-test-helper"));
+  g_ptr_array_add (argv, NULL);
+
+  g_spawn_sync (here,
+                (char **) argv->pdata,
+                envp,
+                G_SPAWN_DEFAULT,
+                NULL,  /* child setup */
+                NULL,  /* user data */
+                &out,
+                &err,
+                &wait_status,
+                &error);
+  g_assert_no_error (error);
+
+  g_test_message ("%s", out);
+  g_test_message ("%s", err);
+  g_assert_nonnull (strstr (err, "this is spawn-test-helper from path-test-subdir"));
+
+#ifdef G_OS_UNIX
+  g_assert_true (WIFEXITED (wait_status));
+  g_assert_cmpint (WEXITSTATUS (wait_status), ==, 5);
+#endif
+
+  g_strfreev (envp);
+  g_free (here);
+  g_free (subdir);
+  g_free (out);
+  g_free (err);
+  g_ptr_array_unref (argv);
+}
+
+static void
+test_search_path_fallback_in_environ (void)
+{
+  GPtrArray *argv = g_ptr_array_new_with_free_func (g_free);
+  gchar *here = g_test_build_filename (G_TEST_BUILT, ".", NULL);
+  gchar *subdir = g_test_build_filename (G_TEST_BUILT, "path-test-subdir", NULL);
+  gchar **envp = g_get_environ ();
+  gchar *out = NULL;
+  gchar *err = NULL;
+  GError *error = NULL;
+  int wait_status = -1;
+
+  g_test_summary ("With G_SPAWN_SEARCH_PATH but no PATH, a fallback is used.");
+  /* We can't make a meaningful assertion about what the fallback *is*,
+   * but we can assert that it *includes* the current working directory. */
+
+  if (g_file_test ("/usr/bin/spawn-test-helper", G_FILE_TEST_IS_EXECUTABLE) ||
+      g_file_test ("/bin/spawn-test-helper", G_FILE_TEST_IS_EXECUTABLE))
+    {
+      g_test_skip ("Not testing fallback with unknown spawn-test-helper "
+                   "executable in /usr/bin:/bin");
+      return;
+    }
+
+  envp = g_environ_unsetenv (envp, "PATH");
+
+  g_ptr_array_add (argv,
+                   g_test_build_filename (G_TEST_BUILT, "spawn-path-search-helper", NULL));
+  g_ptr_array_add (argv, g_strdup ("--search-path"));
+  g_ptr_array_add (argv, g_strdup ("--set-path-in-envp"));
+  g_ptr_array_add (argv, g_strdup (subdir));
+  g_ptr_array_add (argv, g_strdup ("--"));
+  g_ptr_array_add (argv, g_strdup ("spawn-test-helper"));
+  g_ptr_array_add (argv, NULL);
+
+  g_spawn_sync (here,
+                (char **) argv->pdata,
+                envp,
+                G_SPAWN_DEFAULT,
+                NULL,  /* child setup */
+                NULL,  /* user data */
+                &out,
+                &err,
+                &wait_status,
+                &error);
+  g_assert_no_error (error);
+
+  g_test_message ("%s", out);
+  g_test_message ("%s", err);
+  g_assert_nonnull (strstr (err, "this is spawn-test-helper from glib/tests"));
+
+#ifdef G_OS_UNIX
+  g_assert_true (WIFEXITED (wait_status));
+  g_assert_cmpint (WEXITSTATUS (wait_status), ==, 0);
+#endif
+
+  g_strfreev (envp);
+  g_free (here);
+  g_free (subdir);
+  g_free (out);
+  g_free (err);
+  g_ptr_array_unref (argv);
+}
+
+static void
+test_search_path_fallback_in_envp (void)
+{
+  GPtrArray *argv = g_ptr_array_new_with_free_func (g_free);
+  gchar *here = g_test_build_filename (G_TEST_BUILT, ".", NULL);
+  gchar *subdir = g_test_build_filename (G_TEST_BUILT, "path-test-subdir", NULL);
+  gchar **envp = g_get_environ ();
+  gchar *out = NULL;
+  gchar *err = NULL;
+  GError *error = NULL;
+  int wait_status = -1;
+
+  g_test_summary ("With G_SPAWN_SEARCH_PATH_FROM_ENVP but no PATH, a fallback is used.");
+  /* We can't make a meaningful assertion about what the fallback *is*,
+   * but we can assert that it *includes* the current working directory. */
+
+  if (g_file_test ("/usr/bin/spawn-test-helper", G_FILE_TEST_IS_EXECUTABLE) ||
+      g_file_test ("/bin/spawn-test-helper", G_FILE_TEST_IS_EXECUTABLE))
+    {
+      g_test_skip ("Not testing fallback with unknown spawn-test-helper "
+                   "executable in /usr/bin:/bin");
+      return;
+    }
+
+  envp = g_environ_setenv (envp, "PATH", subdir, TRUE);
+
+  g_ptr_array_add (argv,
+                   g_test_build_filename (G_TEST_BUILT, "spawn-path-search-helper", NULL));
+  g_ptr_array_add (argv, g_strdup ("--search-path-from-envp"));
+  g_ptr_array_add (argv, g_strdup ("--unset-path-in-envp"));
+  g_ptr_array_add (argv, g_strdup ("--"));
+  g_ptr_array_add (argv, g_strdup ("spawn-test-helper"));
+  g_ptr_array_add (argv, NULL);
+
+  g_spawn_sync (here,
+                (char **) argv->pdata,
+                envp,
+                G_SPAWN_DEFAULT,
+                NULL,  /* child setup */
+                NULL,  /* user data */
+                &out,
+                &err,
+                &wait_status,
+                &error);
+  g_assert_no_error (error);
+
+  g_test_message ("%s", out);
+  g_test_message ("%s", err);
+  g_assert_nonnull (strstr (err, "this is spawn-test-helper from glib/tests"));
+
+#ifdef G_OS_UNIX
+  g_assert_true (WIFEXITED (wait_status));
+  g_assert_cmpint (WEXITSTATUS (wait_status), ==, 0);
+#endif
+
+  g_strfreev (envp);
+  g_free (here);
+  g_free (subdir);
+  g_free (out);
+  g_free (err);
+  g_ptr_array_unref (argv);
+}
+
+static void
+test_search_path_heap_allocation (void)
+{
+  GPtrArray *argv = g_ptr_array_new_with_free_func (g_free);
+  /* Must be longer than the arbitrary 4000 byte limit for stack allocation
+   * in gspawn.c */
+  char placeholder[4096];
+  gchar *here = g_test_build_filename (G_TEST_BUILT, ".", NULL);
+  gchar *subdir = g_test_build_filename (G_TEST_BUILT, "path-test-subdir", NULL);
+  gchar *long_dir = NULL;
+  gchar *long_path = NULL;
+  gchar **envp = g_get_environ ();
+  gchar *out = NULL;
+  gchar *err = NULL;
+  GError *error = NULL;
+  int wait_status = -1;
+  gsize i;
+
+  memset (placeholder, '_', sizeof (placeholder));
+  /* Force search_path_buffer to be heap-allocated */
+  long_dir = g_test_build_filename (G_TEST_BUILT, "path-test-subdir", placeholder, NULL);
+  long_path = g_strjoin (G_SEARCHPATH_SEPARATOR_S, subdir, long_dir, NULL);
+  envp = g_environ_setenv (envp, "PATH", long_path, TRUE);
+
+  g_ptr_array_add (argv,
+                   g_test_build_filename (G_TEST_BUILT, "spawn-path-search-helper", NULL));
+  g_ptr_array_add (argv, g_strdup ("--search-path"));
+  g_ptr_array_add (argv, g_strdup ("--"));
+  g_ptr_array_add (argv, g_strdup ("spawn-test-helper"));
+
+  /* Add enough arguments to make argv longer than the arbitrary 4000 byte
+   * limit for stack allocation in gspawn.c.
+   * This assumes sizeof (char *) >= 4. */
+  for (i = 0; i < 1001; i++)
+    g_ptr_array_add (argv, g_strdup ("_"));
+
+  g_ptr_array_add (argv, NULL);
+
+  g_spawn_sync (here,
+                (char **) argv->pdata,
+                envp,
+                G_SPAWN_DEFAULT,
+                NULL,  /* child setup */
+                NULL,  /* user data */
+                &out,
+                &err,
+                &wait_status,
+                &error);
+  g_assert_no_error (error);
+
+  g_test_message ("%s", out);
+  g_test_message ("%s", err);
+  g_assert_nonnull (strstr (err, "this is spawn-test-helper from path-test-subdir"));
+
+#ifdef G_OS_UNIX
+  g_assert_true (WIFEXITED (wait_status));
+  g_assert_cmpint (WEXITSTATUS (wait_status), ==, 5);
+#endif
+
+  g_strfreev (envp);
+  g_free (here);
+  g_free (subdir);
+  g_free (out);
+  g_free (err);
+  g_ptr_array_unref (argv);
+}
+
+int
+main (int    argc,
+      char **argv)
+{
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/spawn/do-not-search", test_do_not_search);
+  g_test_add_func ("/spawn/search-path", test_search_path);
+  g_test_add_func ("/spawn/search-path-from-envp", test_search_path_from_envp);
+  g_test_add_func ("/spawn/search-path-ambiguous", test_search_path_ambiguous);
+  g_test_add_func ("/spawn/search-path-heap-allocation",
+                   test_search_path_heap_allocation);
+  g_test_add_func ("/spawn/search-path-fallback-in-environ",
+                   test_search_path_fallback_in_environ);
+  g_test_add_func ("/spawn/search-path-fallback-in-envp",
+                   test_search_path_fallback_in_envp);
+
+  return g_test_run ();
+}
diff --git a/glib/tests/spawn-test-helper.c b/glib/tests/spawn-test-helper.c
new file mode 100644
index 000000000..301f3f31c
--- /dev/null
+++ b/glib/tests/spawn-test-helper.c
@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int main (void)
+{
+  fprintf (stderr, "this is spawn-test-helper from glib/tests\n");
+  return 0;
+}