1 /* provide a replacement fdopendir function
2 Copyright (C) 2004-2021 Free Software Foundation, Inc.
3
4 This program is free software: you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 3 of the License, or
7 (at your option) any later version.
8
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
13
14 You should have received a copy of the GNU General Public License
15 along with this program. If not, see <https://www.gnu.org/licenses/>. */
16
17 /* written by Jim Meyering */
18
19 #include <config.h>
20
21 #include <dirent.h>
22
23 #include <stdlib.h>
24 #include <unistd.h>
25
26 #if !HAVE_FDOPENDIR
27
28 # include "openat.h"
29 # include "openat-priv.h"
30 # include "save-cwd.h"
31
32 # if GNULIB_DIRENT_SAFER
33 # include "dirent--.h"
34 # endif
35
36 # ifndef REPLACE_FCHDIR
37 # define REPLACE_FCHDIR 0
38 # endif
39
40 static DIR *fdopendir_with_dup (int, int, struct saved_cwd const *);
41 static DIR *fd_clone_opendir (int, struct saved_cwd const *);
42
43 /* Replacement for POSIX fdopendir.
44
45 First, try to simulate it via opendir ("/proc/self/fd/..."). Failing
46 that, simulate it by using fchdir metadata, or by doing
47 save_cwd/fchdir/opendir(".")/restore_cwd.
48 If either the save_cwd or the restore_cwd fails (relatively unlikely),
49 then give a diagnostic and exit nonzero.
50
51 If successful, the resulting stream is based on FD in
52 implementations where streams are based on file descriptors and in
53 applications where no other thread or signal handler allocates or
54 frees file descriptors. In other cases, consult dirfd on the result
55 to find out whether FD is still being used.
56
57 Otherwise, this function works just like POSIX fdopendir.
58
59 W A R N I N G:
60
61 Unlike other fd-related functions, this one places constraints on FD.
62 If this function returns successfully, FD is under control of the
63 dirent.h system, and the caller should not close or modify the state of
64 FD other than by the dirent.h functions. */
65 # ifdef __KLIBC__
66 # include <InnoTekLIBC/backend.h>
67
68 DIR *
69 fdopendir (int fd)
70 {
71 char path[_MAX_PATH];
72 DIR *dirp;
73
74 /* Get a path from fd */
75 if (__libc_Back_ioFHToPath (fd, path, sizeof (path)))
76 return NULL;
77
78 dirp = opendir (path);
79 if (!dirp)
80 return NULL;
81
82 /* Unregister fd registered by opendir() */
83 _gl_unregister_dirp_fd (dirfd (dirp));
84
85 /* Register our fd */
86 if (_gl_register_dirp_fd (fd, dirp))
87 {
88 int saved_errno = errno;
89
90 closedir (dirp);
91
92 errno = saved_errno;
93
94 dirp = NULL;
95 }
96
97 return dirp;
98 }
99 # else
100 DIR *
101 fdopendir (int fd)
102 {
103 DIR *dir = fdopendir_with_dup (fd, -1, NULL);
104
105 if (! REPLACE_FCHDIR && ! dir)
106 {
107 int saved_errno = errno;
108 if (EXPECTED_ERRNO (saved_errno))
109 {
110 struct saved_cwd cwd;
111 if (save_cwd (&cwd) != 0)
112 openat_save_fail (errno);
113 dir = fdopendir_with_dup (fd, -1, &cwd);
114 saved_errno = errno;
115 free_cwd (&cwd);
116 errno = saved_errno;
117 }
118 }
119
120 return dir;
121 }
122 # endif
123
124 /* Like fdopendir, except that if OLDER_DUPFD is not -1, it is known
125 to be a dup of FD which is less than FD - 1 and which will be
126 closed by the caller and not otherwise used by the caller. This
127 function makes sure that FD is closed and all file descriptors less
128 than FD are open, and then calls fd_clone_opendir on a dup of FD.
129 That way, barring race conditions, fd_clone_opendir returns a
130 stream whose file descriptor is FD.
131
132 If REPLACE_FCHDIR or CWD is null, use opendir ("/proc/self/fd/...",
133 falling back on fchdir metadata. Otherwise, CWD is a saved version
134 of the working directory; use fchdir/opendir(".")/restore_cwd(CWD). */
135 static DIR *
136 fdopendir_with_dup (int fd, int older_dupfd, struct saved_cwd const *cwd)
137 {
138 int dupfd = dup (fd);
139 if (dupfd < 0 && errno == EMFILE)
140 dupfd = older_dupfd;
141 if (dupfd < 0)
142 return NULL;
143 else
144 {
145 DIR *dir;
146 int saved_errno;
147 if (dupfd < fd - 1 && dupfd != older_dupfd)
148 {
149 dir = fdopendir_with_dup (fd, dupfd, cwd);
150 saved_errno = errno;
151 }
152 else
153 {
154 close (fd);
155 dir = fd_clone_opendir (dupfd, cwd);
156 saved_errno = errno;
157 if (! dir)
158 {
159 int fd1 = dup (dupfd);
160 if (fd1 != fd)
161 openat_save_fail (fd1 < 0 ? errno : EBADF);
162 }
163 }
164
165 if (dupfd != older_dupfd)
166 close (dupfd);
167 errno = saved_errno;
168 return dir;
169 }
170 }
171
172 /* Like fdopendir, except the result controls a clone of FD. It is
173 the caller's responsibility both to close FD and (if the result is
174 not null) to closedir the result. */
175 static DIR *
176 fd_clone_opendir (int fd, struct saved_cwd const *cwd)
177 {
178 if (REPLACE_FCHDIR || ! cwd)
179 {
180 DIR *dir = NULL;
181 int saved_errno = EOPNOTSUPP;
182 char buf[OPENAT_BUFFER_SIZE];
183 char *proc_file = openat_proc_name (buf, fd, ".");
184 if (proc_file)
185 {
186 dir = opendir (proc_file);
187 saved_errno = errno;
188 if (proc_file != buf)
189 free (proc_file);
190 }
191 # if REPLACE_FCHDIR
192 if (! dir && EXPECTED_ERRNO (saved_errno))
193 {
194 char const *name = _gl_directory_name (fd);
195 DIR *dp = name ? opendir (name) : NULL;
196
197 /* The caller has done an elaborate dance to arrange for opendir to
198 consume just the right file descriptor. If dirfd returns -1,
199 though, we're on a system like mingw where opendir does not
200 consume a file descriptor. Consume it via 'dup' instead. */
201 if (dp && dirfd (dp) < 0)
202 dup (fd);
203
204 return dp;
205 }
206 # endif
207 errno = saved_errno;
208 return dir;
209 }
210 else
211 {
212 if (fchdir (fd) != 0)
213 return NULL;
214 else
215 {
216 DIR *dir = opendir (".");
217 int saved_errno = errno;
218 if (restore_cwd (cwd) != 0)
219 openat_restore_fail (errno);
220 errno = saved_errno;
221 return dir;
222 }
223 }
224 }
225
226 #else /* HAVE_FDOPENDIR */
227
228 # include <errno.h>
229 # include <sys/stat.h>
230
231 # undef fdopendir
232
233 /* Like fdopendir, but work around GNU/Hurd bug by validating FD. */
234
235 DIR *
236 rpl_fdopendir (int fd)
237 {
238 struct stat st;
239 if (fstat (fd, &st))
240 return NULL;
241 if (!S_ISDIR (st.st_mode))
242 {
243 errno = ENOTDIR;
244 return NULL;
245 }
246 return fdopendir (fd);
247 }
248
249 #endif /* HAVE_FDOPENDIR */