glib-unix: Add g_closefrom(), g_fdwalk_set_cloexec()

These are the same as Linux `close_range (lowfd, ~0U, 0)` and
`close_range (lowfd, ~0U, CLOSE_RANGE_CLOEXEC)`, but portable.
Unlike some implementations of BSD closefrom(3), they are
async-signal-safe.

The implementations were moved from the GSpawn code, which already
needs all of this functionality anyway, with the exception of
set_cloexec() which was copied (leading to some minor duplication,
but it's very simple).

Resolves: https://gitlab.gnome.org/GNOME/glib/-/issues/3247
Signed-off-by: Simon McVittie <smcv@collabora.com>

glib/glib-unix.c

@@ -1,6 +1,20 @@
 /* GLIB - Library of useful routines for C programming
- * Copyright (C) 2011 Red Hat, Inc.
+ * Copyright 2000-2022 Red Hat, Inc.
- * Copyright 2023 Collabora Ltd.
+ * Copyright 2006-2007 Matthias Clasen
+ * Copyright 2006 Padraig O'Briain
+ * Copyright 2007 Lennart Poettering
+ * Copyright 2018-2022 Endless OS Foundation, LLC
+ * Copyright 2018 Peter Wu
+ * Copyright 2019 Ting-Wei Lan
+ * Copyright 2019 Sebastian Schwarz
+ * Copyright 2020 Matt Rose
+ * Copyright 2021 Casper Dik
+ * Copyright 2022 Alexander Richardson
+ * Copyright 2022 Ray Strode
+ * Copyright 2022 Thomas Haller
+ * Copyright 2023-2024 Collabora Ltd.
+ * Copyright 2023 Sebastian Wilhelmi
+ * Copyright 2023 CaiJingLong
  *
  * glib-unix.c: UNIX specific API wrappers and convenience functions
  *
@@ -28,9 +42,27 @@
 #include "glib-unixprivate.h"
 #include "gmain-internal.h"
 
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>   /* for fdwalk */
 #include <string.h>
 #include <sys/types.h>
 #include <pwd.h>
+#include <unistd.h>
+
+#if defined(__linux__) || defined(__DragonFly__)
+#include <sys/syscall.h>  /* for syscall and SYS_getdents64 */
+#endif
+
+#ifdef HAVE_SYS_RESOURCE_H
+#include <sys/resource.h>
+#endif /* HAVE_SYS_RESOURCE_H */
+
+#if defined(__APPLE__) && defined(HAVE_LIBPROC_H)
+#include <libproc.h>
+#include <sys/proc_info.h>
+#endif
 
 G_STATIC_ASSERT (sizeof (ssize_t) == GLIB_SIZEOF_SSIZE_T);
 G_STATIC_ASSERT (G_ALIGNOF (gssize) == G_ALIGNOF (ssize_t));
@@ -507,3 +539,388 @@ g_unix_get_passwd_entry (const gchar  *user_name,
 
   return (struct passwd *) g_steal_pointer (&buffer);
 }
+
+/* This function is called between fork() and exec() and hence must be
+ * async-signal-safe (see signal-safety(7)). */
+static int
+set_cloexec (void *data, gint fd)
+{
+  if (fd >= GPOINTER_TO_INT (data))
+    fcntl (fd, F_SETFD, FD_CLOEXEC);
+
+  return 0;
+}
+
+/* fdwalk()-compatible callback to close a fd for non-compliant
+ * implementations of fdwalk() that potentially pass already
+ * closed fds.
+ *
+ * It is not an error to pass an invalid fd to this function.
+ *
+ * This function is called between fork() and exec() and hence must be
+ * async-signal-safe (see signal-safety(7)).
+ */
+G_GNUC_UNUSED static int
+close_func_with_invalid_fds (void *data, int fd)
+{
+  /* We use close and not g_close here because on some platforms, we
+   * don't know how to close only valid, open file descriptors, so we
+   * have to pass bad fds to close too. g_close warns if given a bad
+   * fd.
+   *
+   * This function returns no error, because there is nothing that the caller
+   * could do with that information. That is even the case for EINTR. See
+   * g_close() about the specialty of EINTR and why that is correct.
+   * If g_close() ever gets extended to handle EINTR specially, then this place
+   * should get updated to do the same handling.
+   */
+  if (fd >= GPOINTER_TO_INT (data))
+    close (fd);
+
+  return 0;
+}
+
+#ifdef __linux__
+struct linux_dirent64
+{
+  guint64        d_ino;    /* 64-bit inode number */
+  guint64        d_off;    /* 64-bit offset to next structure */
+  unsigned short d_reclen; /* Size of this dirent */
+  unsigned char  d_type;   /* File type */
+  char           d_name[]; /* Filename (null-terminated) */
+};
+
+/* This function is called between fork() and exec() and hence must be
+ * async-signal-safe (see signal-safety(7)). */
+static gint
+filename_to_fd (const char *p)
+{
+  char c;
+  int fd = 0;
+  const int cutoff = G_MAXINT / 10;
+  const int cutlim = G_MAXINT % 10;
+
+  if (*p == '\0')
+    return -1;
+
+  while ((c = *p++) != '\0')
+    {
+      if (c < '0' || c > '9')
+        return -1;
+      c -= '0';
+
+      /* Check for overflow. */
+      if (fd > cutoff || (fd == cutoff && c > cutlim))
+        return -1;
+
+      fd = fd * 10 + c;
+    }
+
+  return fd;
+}
+#endif
+
+static int safe_fdwalk_with_invalid_fds (int (*cb)(void *data, int fd), void *data);
+
+/* This function is called between fork() and exec() and hence must be
+ * async-signal-safe (see signal-safety(7)). */
+static int
+safe_fdwalk (int (*cb)(void *data, int fd), void *data)
+{
+#if 0
+  /* Use fdwalk function provided by the system if it is known to be
+   * async-signal safe.
+   *
+   * Currently there are no operating systems known to provide a safe
+   * implementation, so this section is not used for now.
+   */
+  return fdwalk (cb, data);
+#else
+  /* Fallback implementation of fdwalk. It should be async-signal safe, but it
+   * may fail on non-Linux operating systems. See safe_fdwalk_with_invalid_fds
+   * for a slower alternative.
+   */
+
+#ifdef __linux__
+  gint fd;
+  gint res = 0;
+
+  /* Avoid use of opendir/closedir since these are not async-signal-safe. */
+  int dir_fd = open ("/proc/self/fd", O_RDONLY | O_DIRECTORY);
+  if (dir_fd >= 0)
+    {
+      /* buf needs to be aligned correctly to receive linux_dirent64.
+       * C11 has _Alignof for this purpose, but for now a
+       * union serves the same purpose. */
+      union
+      {
+        char buf[4096];
+        struct linux_dirent64 alignment;
+      } u;
+      int pos, nread;
+      struct linux_dirent64 *de;
+
+      while ((nread = syscall (SYS_getdents64, dir_fd, u.buf, sizeof (u.buf))) > 0)
+        {
+          for (pos = 0; pos < nread; pos += de->d_reclen)
+            {
+              de = (struct linux_dirent64 *) (u.buf + pos);
+
+              fd = filename_to_fd (de->d_name);
+              if (fd < 0 || fd == dir_fd)
+                  continue;
+
+              if ((res = cb (data, fd)) != 0)
+                  break;
+            }
+        }
+
+      g_close (dir_fd, NULL);
+      return res;
+    }
+
+  /* If /proc is not mounted or not accessible we fail here and rely on
+   * safe_fdwalk_with_invalid_fds to fall back to the old
+   * rlimit trick. */
+
+#endif
+
+#if defined(__sun__) && defined(F_PREVFD) && defined(F_NEXTFD)
+/*
+ * Solaris 11.4 has a signal-safe way which allows
+ * us to find all file descriptors in a process.
+ *
+ * fcntl(fd, F_NEXTFD, maxfd)
+ * - returns the first allocated file descriptor <= maxfd  > fd.
+ *
+ * fcntl(fd, F_PREVFD)
+ * - return highest allocated file descriptor < fd.
+ */
+  gint fd;
+  gint res = 0;
+
+  open_max = fcntl (INT_MAX, F_PREVFD); /* find the maximum fd */
+  if (open_max < 0) /* No open files */
+    return 0;
+
+  for (fd = -1; (fd = fcntl (fd, F_NEXTFD, open_max)) != -1; )
+    if ((res = cb (data, fd)) != 0 || fd == open_max)
+      break;
+
+  return res;
+#endif
+
+  return safe_fdwalk_with_invalid_fds (cb, data);
+#endif
+}
+
+/* This function is called between fork() and exec() and hence must be
+ * async-signal-safe (see signal-safety(7)). */
+static int
+safe_fdwalk_with_invalid_fds (int (*cb)(void *data, int fd), void *data)
+{
+  /* Fallback implementation of fdwalk. It should be async-signal safe, but it
+   * may be slow, especially on systems allowing very high number of open file
+   * descriptors.
+   */
+  gint open_max = -1;
+  gint fd;
+  gint res = 0;
+
+#if 0 && defined(HAVE_SYS_RESOURCE_H)
+  struct rlimit rl;
+
+  /* Use getrlimit() function provided by the system if it is known to be
+   * async-signal safe.
+   *
+   * Currently there are no operating systems known to provide a safe
+   * implementation, so this section is not used for now.
+   */
+  if (getrlimit (RLIMIT_NOFILE, &rl) == 0 && rl.rlim_max != RLIM_INFINITY)
+    open_max = rl.rlim_max;
+#endif
+#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__APPLE__)
+  /* Use sysconf() function provided by the system if it is known to be
+   * async-signal safe.
+   *
+   * FreeBSD: sysconf() is included in the list of async-signal safe functions
+   * found in https://man.freebsd.org/sigaction(2).
+   *
+   * OpenBSD: sysconf() is included in the list of async-signal safe functions
+   * found in https://man.openbsd.org/sigaction.2.
+   *
+   * Apple: sysconf() is included in the list of async-signal safe functions
+   * found in https://opensource.apple.com/source/xnu/xnu-517.12.7/bsd/man/man2/sigaction.2
+   */
+  if (open_max < 0)
+    open_max = sysconf (_SC_OPEN_MAX);
+#endif
+  /* Hardcoded fallback: the default process hard limit in Linux as of 2020 */
+  if (open_max < 0)
+    open_max = 4096;
+
+#if defined(__APPLE__) && defined(HAVE_LIBPROC_H)
+  /* proc_pidinfo isn't documented as async-signal-safe but looking at the implementation
+   * in the darwin tree here:
+   *
+   * https://opensource.apple.com/source/Libc/Libc-498/darwin/libproc.c.auto.html
+   *
+   * It's just a thin wrapper around a syscall, so it's probably okay.
+   */
+  {
+    char buffer[4096 * PROC_PIDLISTFD_SIZE];
+    ssize_t buffer_size;
+
+    buffer_size = proc_pidinfo (getpid (), PROC_PIDLISTFDS, 0, buffer, sizeof (buffer));
+
+    if (buffer_size > 0 &&
+        sizeof (buffer) >= (size_t) buffer_size &&
+        (buffer_size % PROC_PIDLISTFD_SIZE) == 0)
+      {
+        const struct proc_fdinfo *fd_info = (const struct proc_fdinfo *) buffer;
+        size_t number_of_fds = (size_t) buffer_size / PROC_PIDLISTFD_SIZE;
+
+        for (size_t i = 0; i < number_of_fds; i++)
+          if ((res = cb (data, fd_info[i].proc_fd)) != 0)
+            break;
+
+        return res;
+      }
+  }
+#endif
+
+  for (fd = 0; fd < open_max; fd++)
+      if ((res = cb (data, fd)) != 0)
+          break;
+
+  return res;
+}
+
+/**
+ * g_fdwalk_set_cloexec:
+ * @lowfd: Minimum fd to act on, which must be non-negative
+ *
+ * Mark every file descriptor equal to or greater than @lowfd to be closed
+ * at the next `execve()` or similar, as if via the `FD_CLOEXEC` flag.
+ *
+ * Typically @lowfd will be 3, to leave standard input, standard output
+ * and standard error open after exec.
+ *
+ * This is the same as Linux `close_range (lowfd, ~0U, CLOSE_RANGE_CLOEXEC)`,
+ * but portable to other OSs and to older versions of Linux.
+ *
+ * This function is async-signal safe, making it safe to call from a
+ * signal handler or a [callback@GLib.SpawnChildSetupFunc], as long as @lowfd is
+ * non-negative.
+ * See [`signal(7)`](man:signal(7)) and
+ * [`signal-safety(7)`](man:signal-safety(7)) for more details.
+ *
+ * Returns: 0 on success, -1 with errno set on error
+ * Since: 2.80
+ */
+int
+g_fdwalk_set_cloexec (int lowfd)
+{
+  int ret;
+
+  g_return_val_if_fail (lowfd >= 0, (errno = EINVAL, -1));
+
+#if defined(HAVE_CLOSE_RANGE) && defined(CLOSE_RANGE_CLOEXEC)
+  /* close_range() is available in Linux since kernel 5.9, and on FreeBSD at
+   * around the same time. It was designed for use in async-signal-safe
+   * situations: https://bugs.python.org/issue38061
+   *
+   * The `CLOSE_RANGE_CLOEXEC` flag was added in Linux 5.11, and is not yet
+   * present in FreeBSD.
+   *
+   * Handle ENOSYS in case it’s supported in libc but not the kernel; if so,
+   * fall back to safe_fdwalk(). Handle EINVAL in case `CLOSE_RANGE_CLOEXEC`
+   * is not supported. */
+  ret = close_range (lowfd, G_MAXUINT, CLOSE_RANGE_CLOEXEC);
+  if (ret == 0 || !(errno == ENOSYS || errno == EINVAL))
+    return ret;
+#endif  /* HAVE_CLOSE_RANGE */
+
+  ret = safe_fdwalk (set_cloexec, GINT_TO_POINTER (lowfd));
+
+  return ret;
+}
+
+/**
+ * g_closefrom:
+ * @lowfd: Minimum fd to close, which must be non-negative
+ *
+ * Close every file descriptor equal to or greater than @lowfd.
+ *
+ * Typically @lowfd will be 3, to leave standard input, standard output
+ * and standard error open.
+ *
+ * This is the same as Linux `close_range (lowfd, ~0U, 0)`,
+ * but portable to other OSs and to older versions of Linux.
+ * Equivalently, it is the same as BSD `closefrom (lowfd)`, but portable,
+ * and async-signal-safe on all OSs.
+ *
+ * This function is async-signal safe, making it safe to call from a
+ * signal handler or a [callback@GLib.SpawnChildSetupFunc], as long as @lowfd is
+ * non-negative.
+ * See [`signal(7)`](man:signal(7)) and
+ * [`signal-safety(7)`](man:signal-safety(7)) for more details.
+ *
+ * Returns: 0 on success, -1 with errno set on error
+ * Since: 2.80
+ */
+int
+g_closefrom (int lowfd)
+{
+  int ret;
+
+  g_return_val_if_fail (lowfd >= 0, (errno = EINVAL, -1));
+
+#if defined(HAVE_CLOSE_RANGE)
+  /* close_range() is available in Linux since kernel 5.9, and on FreeBSD at
+   * around the same time. It was designed for use in async-signal-safe
+   * situations: https://bugs.python.org/issue38061
+   *
+   * Handle ENOSYS in case it’s supported in libc but not the kernel; if so,
+   * fall back to safe_fdwalk(). */
+  ret = close_range (lowfd, G_MAXUINT, 0);
+  if (ret == 0 || errno != ENOSYS)
+    return ret;
+#endif  /* HAVE_CLOSE_RANGE */
+
+#if defined(__FreeBSD__) || defined(__OpenBSD__) || \
+  (defined(__sun__) && defined(F_CLOSEFROM))
+  /* Use closefrom function provided by the system if it is known to be
+   * async-signal safe.
+   *
+   * FreeBSD: closefrom is included in the list of async-signal safe functions
+   * found in https://man.freebsd.org/sigaction(2).
+   *
+   * OpenBSD: closefrom is not included in the list, but a direct system call
+   * should be safe to use.
+   *
+   * In Solaris as of 11.3 SRU 31, closefrom() is also a direct system call.
+   * On such systems, F_CLOSEFROM is defined.
+   */
+  (void) closefrom (lowfd);
+  return 0;
+#elif defined(__DragonFly__)
+  /* It is unclear whether closefrom function included in DragonFlyBSD libc_r
+   * is safe to use because it calls a lot of library functions. It is also
+   * unclear whether libc_r itself is still being used. Therefore, we do a
+   * direct system call here ourselves to avoid possible issues.
+   */
+  (void) syscall (SYS_closefrom, lowfd);
+  return 0;
+#elif defined(F_CLOSEM)
+  /* NetBSD and AIX have a special fcntl command which does the same thing as
+   * closefrom. NetBSD also includes closefrom function, which seems to be a
+   * simple wrapper of the fcntl command.
+   */
+  return fcntl (lowfd, F_CLOSEM);
+#else
+  ret = safe_fdwalk (close_func_with_invalid_fds, GINT_TO_POINTER (lowfd));
+
+  return ret;
+#endif
+}

glib/glib-unix.h

@@ -326,6 +326,12 @@ g_unix_pipe_clear (GUnixPipe *self)
 
 G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC (GUnixPipe, g_unix_pipe_clear)
 
+GLIB_AVAILABLE_IN_2_80
+int g_closefrom (int lowfd);
+
+GLIB_AVAILABLE_IN_2_80
+int g_fdwalk_set_cloexec (int lowfd);
+
 G_GNUC_END_IGNORE_DEPRECATIONS
 
 G_END_DECLS

glib/gspawn.c

@@ -1265,337 +1265,6 @@ dupfd_cloexec (int old_fd, int new_fd_min)
   return fd;
 }
 
-/* fdwalk()-compatible callback to close a fd for non-compliant
- * implementations of fdwalk() that potentially pass already
- * closed fds.
- *
- * It is not an error to pass an invalid fd to this function.
- *
- * This function is called between fork() and exec() and hence must be
- * async-signal-safe (see signal-safety(7)).
- */
-G_GNUC_UNUSED static int
-close_func_with_invalid_fds (void *data, int fd)
-{
-  /* We use close and not g_close here because on some platforms, we
-   * don't know how to close only valid, open file descriptors, so we
-   * have to pass bad fds to close too. g_close warns if given a bad
-   * fd.
-   *
-   * This function returns no error, because there is nothing that the caller
-   * could do with that information. That is even the case for EINTR. See
-   * g_close() about the specialty of EINTR and why that is correct.
-   * If g_close() ever gets extended to handle EINTR specially, then this place
-   * should get updated to do the same handling.
-   */
-  if (fd >= GPOINTER_TO_INT (data))
-    close (fd);
-
-  return 0;
-}
-
-#ifdef __linux__
-struct linux_dirent64
-{
-  guint64        d_ino;    /* 64-bit inode number */
-  guint64        d_off;    /* 64-bit offset to next structure */
-  unsigned short d_reclen; /* Size of this dirent */
-  unsigned char  d_type;   /* File type */
-  char           d_name[]; /* Filename (null-terminated) */
-};
-
-/* This function is called between fork() and exec() and hence must be
- * async-signal-safe (see signal-safety(7)). */
-static gint
-filename_to_fd (const char *p)
-{
-  char c;
-  int fd = 0;
-  const int cutoff = G_MAXINT / 10;
-  const int cutlim = G_MAXINT % 10;
-
-  if (*p == '\0')
-    return -1;
-
-  while ((c = *p++) != '\0')
-    {
-      if (c < '0' || c > '9')
-        return -1;
-      c -= '0';
-
-      /* Check for overflow. */
-      if (fd > cutoff || (fd == cutoff && c > cutlim))
-        return -1;
-
-      fd = fd * 10 + c;
-    }
-
-  return fd;
-}
-#endif
-
-static int safe_fdwalk_with_invalid_fds (int (*cb)(void *data, int fd), void *data);
-
-/* This function is called between fork() and exec() and hence must be
- * async-signal-safe (see signal-safety(7)). */
-static int
-safe_fdwalk (int (*cb)(void *data, int fd), void *data)
-{
-#if 0
-  /* Use fdwalk function provided by the system if it is known to be
-   * async-signal safe.
-   *
-   * Currently there are no operating systems known to provide a safe
-   * implementation, so this section is not used for now.
-   */
-  return fdwalk (cb, data);
-#else
-  /* Fallback implementation of fdwalk. It should be async-signal safe, but it
-   * may fail on non-Linux operating systems. See safe_fdwalk_with_invalid_fds
-   * for a slower alternative.
-   */
-
-#ifdef __linux__
-  gint fd;
-  gint res = 0;
-
-  /* Avoid use of opendir/closedir since these are not async-signal-safe. */
-  int dir_fd = open ("/proc/self/fd", O_RDONLY | O_DIRECTORY);
-  if (dir_fd >= 0)
-    {
-      /* buf needs to be aligned correctly to receive linux_dirent64.
-       * C11 has _Alignof for this purpose, but for now a
-       * union serves the same purpose. */
-      union
-      {
-        char buf[4096];
-        struct linux_dirent64 alignment;
-      } u;
-      int pos, nread;
-      struct linux_dirent64 *de;
-
-      while ((nread = syscall (SYS_getdents64, dir_fd, u.buf, sizeof (u.buf))) > 0)
-        {
-          for (pos = 0; pos < nread; pos += de->d_reclen)
-            {
-              de = (struct linux_dirent64 *) (u.buf + pos);
-
-              fd = filename_to_fd (de->d_name);
-              if (fd < 0 || fd == dir_fd)
-                  continue;
-
-              if ((res = cb (data, fd)) != 0)
-                  break;
-            }
-        }
-
-      g_close (dir_fd, NULL);
-      return res;
-    }
-
-  /* If /proc is not mounted or not accessible we fail here and rely on
-   * safe_fdwalk_with_invalid_fds to fall back to the old
-   * rlimit trick. */
-
-#endif
-
-#if defined(__sun__) && defined(F_PREVFD) && defined(F_NEXTFD)
-/*
- * Solaris 11.4 has a signal-safe way which allows
- * us to find all file descriptors in a process.
- *
- * fcntl(fd, F_NEXTFD, maxfd)
- * - returns the first allocated file descriptor <= maxfd  > fd.
- *
- * fcntl(fd, F_PREVFD)
- * - return highest allocated file descriptor < fd.
- */
-  gint fd;
-  gint res = 0;
-
-  open_max = fcntl (INT_MAX, F_PREVFD); /* find the maximum fd */
-  if (open_max < 0) /* No open files */
-    return 0;
-
-  for (fd = -1; (fd = fcntl (fd, F_NEXTFD, open_max)) != -1; )
-    if ((res = cb (data, fd)) != 0 || fd == open_max)
-      break;
-
-  return res;
-#endif
-
-  return safe_fdwalk_with_invalid_fds (cb, data);
-#endif
-}
-
-/* This function is called between fork() and exec() and hence must be
- * async-signal-safe (see signal-safety(7)). */
-static int
-safe_fdwalk_with_invalid_fds (int (*cb)(void *data, int fd), void *data)
-{
-  /* Fallback implementation of fdwalk. It should be async-signal safe, but it
-   * may be slow, especially on systems allowing very high number of open file
-   * descriptors.
-   */
-  gint open_max = -1;
-  gint fd;
-  gint res = 0;
-
-#if 0 && defined(HAVE_SYS_RESOURCE_H)
-  struct rlimit rl;
-
-  /* Use getrlimit() function provided by the system if it is known to be
-   * async-signal safe.
-   *
-   * Currently there are no operating systems known to provide a safe
-   * implementation, so this section is not used for now.
-   */
-  if (getrlimit (RLIMIT_NOFILE, &rl) == 0 && rl.rlim_max != RLIM_INFINITY)
-    open_max = rl.rlim_max;
-#endif
-#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__APPLE__)
-  /* Use sysconf() function provided by the system if it is known to be
-   * async-signal safe.
-   *
-   * FreeBSD: sysconf() is included in the list of async-signal safe functions
-   * found in https://man.freebsd.org/sigaction(2).
-   *
-   * OpenBSD: sysconf() is included in the list of async-signal safe functions
-   * found in https://man.openbsd.org/sigaction.2.
-   * 
-   * Apple: sysconf() is included in the list of async-signal safe functions
-   * found in https://opensource.apple.com/source/xnu/xnu-517.12.7/bsd/man/man2/sigaction.2
-   */
-  if (open_max < 0)
-    open_max = sysconf (_SC_OPEN_MAX);
-#endif
-  /* Hardcoded fallback: the default process hard limit in Linux as of 2020 */
-  if (open_max < 0)
-    open_max = 4096;
-
-#if defined(__APPLE__) && defined(HAVE_LIBPROC_H)
-  /* proc_pidinfo isn't documented as async-signal-safe but looking at the implementation
-   * in the darwin tree here:
-   *
-   * https://opensource.apple.com/source/Libc/Libc-498/darwin/libproc.c.auto.html
-   *
-   * It's just a thin wrapper around a syscall, so it's probably okay.
-   */
-  {
-    char buffer[4096 * PROC_PIDLISTFD_SIZE];
-    ssize_t buffer_size;
-
-    buffer_size = proc_pidinfo (getpid (), PROC_PIDLISTFDS, 0, buffer, sizeof (buffer));
-
-    if (buffer_size > 0 &&
-        sizeof (buffer) >= (size_t) buffer_size &&
-        (buffer_size % PROC_PIDLISTFD_SIZE) == 0)
-      {
-        const struct proc_fdinfo *fd_info = (const struct proc_fdinfo *) buffer;
-        size_t number_of_fds = (size_t) buffer_size / PROC_PIDLISTFD_SIZE;
-
-        for (size_t i = 0; i < number_of_fds; i++)
-          if ((res = cb (data, fd_info[i].proc_fd)) != 0)
-            break;
-
-        return res;
-      }
-  }
-#endif
-
-  for (fd = 0; fd < open_max; fd++)
-      if ((res = cb (data, fd)) != 0)
-          break;
-
-  return res;
-}
-
-/* This function is called between fork() and exec() and hence must be
- * async-signal-safe (see signal-safety(7)). */
-static int
-safe_fdwalk_set_cloexec (int lowfd)
-{
-  int ret;
-
-#if defined(HAVE_CLOSE_RANGE) && defined(CLOSE_RANGE_CLOEXEC)
-  /* close_range() is available in Linux since kernel 5.9, and on FreeBSD at
-   * around the same time. It was designed for use in async-signal-safe
-   * situations: https://bugs.python.org/issue38061
-   *
-   * The `CLOSE_RANGE_CLOEXEC` flag was added in Linux 5.11, and is not yet
-   * present in FreeBSD.
-   *
-   * Handle ENOSYS in case it’s supported in libc but not the kernel; if so,
-   * fall back to safe_fdwalk(). Handle EINVAL in case `CLOSE_RANGE_CLOEXEC`
-   * is not supported. */
-  ret = close_range (lowfd, G_MAXUINT, CLOSE_RANGE_CLOEXEC);
-  if (ret == 0 || !(errno == ENOSYS || errno == EINVAL))
-    return ret;
-#endif  /* HAVE_CLOSE_RANGE */
-
-  ret = safe_fdwalk (set_cloexec, GINT_TO_POINTER (lowfd));
-
-  return ret;
-}
-
-/* This function is called between fork() and exec() and hence must be
- * async-signal-safe (see signal-safety(7)).
- *
- * On failure, `-1` will be returned and errno will be set. */
-static int
-safe_closefrom (int lowfd)
-{
-  int ret;
-
-#if defined(HAVE_CLOSE_RANGE)
-  /* close_range() is available in Linux since kernel 5.9, and on FreeBSD at
-   * around the same time. It was designed for use in async-signal-safe
-   * situations: https://bugs.python.org/issue38061
-   *
-   * Handle ENOSYS in case it’s supported in libc but not the kernel; if so,
-   * fall back to safe_fdwalk(). */
-  ret = close_range (lowfd, G_MAXUINT, 0);
-  if (ret == 0 || errno != ENOSYS)
-    return ret;
-#endif  /* HAVE_CLOSE_RANGE */
-
-#if defined(__FreeBSD__) || defined(__OpenBSD__) || \
-  (defined(__sun__) && defined(F_CLOSEFROM))
-  /* Use closefrom function provided by the system if it is known to be
-   * async-signal safe.
-   *
-   * FreeBSD: closefrom is included in the list of async-signal safe functions
-   * found in https://man.freebsd.org/sigaction(2).
-   *
-   * OpenBSD: closefrom is not included in the list, but a direct system call
-   * should be safe to use.
-   *
-   * In Solaris as of 11.3 SRU 31, closefrom() is also a direct system call.
-   * On such systems, F_CLOSEFROM is defined.
-   */
-  (void) closefrom (lowfd);
-  return 0;
-#elif defined(__DragonFly__)
-  /* It is unclear whether closefrom function included in DragonFlyBSD libc_r
-   * is safe to use because it calls a lot of library functions. It is also
-   * unclear whether libc_r itself is still being used. Therefore, we do a
-   * direct system call here ourselves to avoid possible issues.
-   */
-  (void) syscall (SYS_closefrom, lowfd);
-  return 0;
-#elif defined(F_CLOSEM)
-  /* NetBSD and AIX have a special fcntl command which does the same thing as
-   * closefrom. NetBSD also includes closefrom function, which seems to be a
-   * simple wrapper of the fcntl command.
-   */
-  return fcntl (lowfd, F_CLOSEM);
-#else
-  ret = safe_fdwalk (close_func_with_invalid_fds, GINT_TO_POINTER (lowfd));
-
-  return ret;
-#endif
-}
-
 /* This function is called between fork() and exec() and hence must be
  * async-signal-safe (see signal-safety(7)). */
 static gint
@@ -1823,13 +1492,13 @@ do_exec (gint                  child_err_report_fd,
           if (safe_dup2 (child_err_report_fd, 3) < 0)
             write_err_and_exit (child_err_report_fd, CHILD_DUPFD_FAILED);
           set_cloexec (GINT_TO_POINTER (0), 3);
-          if (safe_closefrom (4) < 0)
+          if (g_closefrom (4) < 0)
             write_err_and_exit (child_err_report_fd, CHILD_CLOSE_FAILED);
           child_err_report_fd = 3;
         }
       else
         {
-          if (safe_fdwalk_set_cloexec (3) < 0)
+          if (g_fdwalk_set_cloexec (3) < 0)
             write_err_and_exit (child_err_report_fd, CHILD_CLOSE_FAILED);
         }
     }