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-rw-r--r--lib/fdopendir.c249
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diff --git a/lib/fdopendir.c b/lib/fdopendir.c
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--- /dev/null
+++ b/lib/fdopendir.c
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+/* provide a replacement fdopendir function
+ Copyright (C) 2004-2022 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program 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 General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>. */
+
+/* written by Jim Meyering */
+
+#include <config.h>
+
+#include <dirent.h>
+
+#include <stdlib.h>
+#include <unistd.h>
+
+#if !HAVE_FDOPENDIR
+
+# include "openat.h"
+# include "openat-priv.h"
+# include "save-cwd.h"
+
+# if GNULIB_DIRENT_SAFER
+# include "dirent--.h"
+# endif
+
+# ifndef REPLACE_FCHDIR
+# define REPLACE_FCHDIR 0
+# endif
+
+static DIR *fdopendir_with_dup (int, int, struct saved_cwd const *);
+static DIR *fd_clone_opendir (int, struct saved_cwd const *);
+
+/* Replacement for POSIX fdopendir.
+
+ First, try to simulate it via opendir ("/proc/self/fd/..."). Failing
+ that, simulate it by using fchdir metadata, or by doing
+ save_cwd/fchdir/opendir(".")/restore_cwd.
+ If either the save_cwd or the restore_cwd fails (relatively unlikely),
+ then give a diagnostic and exit nonzero.
+
+ If successful, the resulting stream is based on FD in
+ implementations where streams are based on file descriptors and in
+ applications where no other thread or signal handler allocates or
+ frees file descriptors. In other cases, consult dirfd on the result
+ to find out whether FD is still being used.
+
+ Otherwise, this function works just like POSIX fdopendir.
+
+ W A R N I N G:
+
+ Unlike other fd-related functions, this one places constraints on FD.
+ If this function returns successfully, FD is under control of the
+ dirent.h system, and the caller should not close or modify the state of
+ FD other than by the dirent.h functions. */
+# ifdef __KLIBC__
+# include <InnoTekLIBC/backend.h>
+
+DIR *
+fdopendir (int fd)
+{
+ char path[_MAX_PATH];
+ DIR *dirp;
+
+ /* Get a path from fd */
+ if (__libc_Back_ioFHToPath (fd, path, sizeof (path)))
+ return NULL;
+
+ dirp = opendir (path);
+ if (!dirp)
+ return NULL;
+
+ /* Unregister fd registered by opendir() */
+ _gl_unregister_dirp_fd (dirfd (dirp));
+
+ /* Register our fd */
+ if (_gl_register_dirp_fd (fd, dirp))
+ {
+ int saved_errno = errno;
+
+ closedir (dirp);
+
+ errno = saved_errno;
+
+ dirp = NULL;
+ }
+
+ return dirp;
+}
+# else
+DIR *
+fdopendir (int fd)
+{
+ DIR *dir = fdopendir_with_dup (fd, -1, NULL);
+
+ if (! REPLACE_FCHDIR && ! dir)
+ {
+ int saved_errno = errno;
+ if (EXPECTED_ERRNO (saved_errno))
+ {
+ struct saved_cwd cwd;
+ if (save_cwd (&cwd) != 0)
+ openat_save_fail (errno);
+ dir = fdopendir_with_dup (fd, -1, &cwd);
+ saved_errno = errno;
+ free_cwd (&cwd);
+ errno = saved_errno;
+ }
+ }
+
+ return dir;
+}
+# endif
+
+/* Like fdopendir, except that if OLDER_DUPFD is not -1, it is known
+ to be a dup of FD which is less than FD - 1 and which will be
+ closed by the caller and not otherwise used by the caller. This
+ function makes sure that FD is closed and all file descriptors less
+ than FD are open, and then calls fd_clone_opendir on a dup of FD.
+ That way, barring race conditions, fd_clone_opendir returns a
+ stream whose file descriptor is FD.
+
+ If REPLACE_FCHDIR or CWD is null, use opendir ("/proc/self/fd/...",
+ falling back on fchdir metadata. Otherwise, CWD is a saved version
+ of the working directory; use fchdir/opendir(".")/restore_cwd(CWD). */
+static DIR *
+fdopendir_with_dup (int fd, int older_dupfd, struct saved_cwd const *cwd)
+{
+ int dupfd = dup (fd);
+ if (dupfd < 0 && errno == EMFILE)
+ dupfd = older_dupfd;
+ if (dupfd < 0)
+ return NULL;
+ else
+ {
+ DIR *dir;
+ int saved_errno;
+ if (dupfd < fd - 1 && dupfd != older_dupfd)
+ {
+ dir = fdopendir_with_dup (fd, dupfd, cwd);
+ saved_errno = errno;
+ }
+ else
+ {
+ close (fd);
+ dir = fd_clone_opendir (dupfd, cwd);
+ saved_errno = errno;
+ if (! dir)
+ {
+ int fd1 = dup (dupfd);
+ if (fd1 != fd)
+ openat_save_fail (fd1 < 0 ? errno : EBADF);
+ }
+ }
+
+ if (dupfd != older_dupfd)
+ close (dupfd);
+ errno = saved_errno;
+ return dir;
+ }
+}
+
+/* Like fdopendir, except the result controls a clone of FD. It is
+ the caller's responsibility both to close FD and (if the result is
+ not null) to closedir the result. */
+static DIR *
+fd_clone_opendir (int fd, struct saved_cwd const *cwd)
+{
+ if (REPLACE_FCHDIR || ! cwd)
+ {
+ DIR *dir = NULL;
+ int saved_errno = EOPNOTSUPP;
+ char buf[OPENAT_BUFFER_SIZE];
+ char *proc_file = openat_proc_name (buf, fd, ".");
+ if (proc_file)
+ {
+ dir = opendir (proc_file);
+ saved_errno = errno;
+ if (proc_file != buf)
+ free (proc_file);
+ }
+# if REPLACE_FCHDIR
+ if (! dir && EXPECTED_ERRNO (saved_errno))
+ {
+ char const *name = _gl_directory_name (fd);
+ DIR *dp = name ? opendir (name) : NULL;
+
+ /* The caller has done an elaborate dance to arrange for opendir to
+ consume just the right file descriptor. If dirfd returns -1,
+ though, we're on a system like mingw where opendir does not
+ consume a file descriptor. Consume it via 'dup' instead. */
+ if (dp && dirfd (dp) < 0)
+ dup (fd);
+
+ return dp;
+ }
+# endif
+ errno = saved_errno;
+ return dir;
+ }
+ else
+ {
+ if (fchdir (fd) != 0)
+ return NULL;
+ else
+ {
+ DIR *dir = opendir (".");
+ int saved_errno = errno;
+ if (restore_cwd (cwd) != 0)
+ openat_restore_fail (errno);
+ errno = saved_errno;
+ return dir;
+ }
+ }
+}
+
+#else /* HAVE_FDOPENDIR */
+
+# include <errno.h>
+# include <sys/stat.h>
+
+# undef fdopendir
+
+/* Like fdopendir, but work around GNU/Hurd bug by validating FD. */
+
+DIR *
+rpl_fdopendir (int fd)
+{
+ struct stat st;
+ if (fstat (fd, &st))
+ return NULL;
+ if (!S_ISDIR (st.st_mode))
+ {
+ errno = ENOTDIR;
+ return NULL;
+ }
+ return fdopendir (fd);
+}
+
+#endif /* HAVE_FDOPENDIR */