Commit | Line | Data |
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8654f9d7 | 1 | /* provide a replacement fdopendir function |
ba318903 | 2 | Copyright (C) 2004-2014 Free Software Foundation, Inc. |
8654f9d7 PE |
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 <http://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 | DIR * | |
66 | fdopendir (int fd) | |
67 | { | |
68 | DIR *dir = fdopendir_with_dup (fd, -1, NULL); | |
69 | ||
70 | if (! REPLACE_FCHDIR && ! dir) | |
71 | { | |
72 | int saved_errno = errno; | |
73 | if (EXPECTED_ERRNO (saved_errno)) | |
74 | { | |
75 | struct saved_cwd cwd; | |
76 | if (save_cwd (&cwd) != 0) | |
77 | openat_save_fail (errno); | |
78 | dir = fdopendir_with_dup (fd, -1, &cwd); | |
79 | saved_errno = errno; | |
80 | free_cwd (&cwd); | |
81 | errno = saved_errno; | |
82 | } | |
83 | } | |
84 | ||
85 | return dir; | |
86 | } | |
87 | ||
88 | /* Like fdopendir, except that if OLDER_DUPFD is not -1, it is known | |
89 | to be a dup of FD which is less than FD - 1 and which will be | |
90 | closed by the caller and not otherwise used by the caller. This | |
91 | function makes sure that FD is closed and all file descriptors less | |
92 | than FD are open, and then calls fd_clone_opendir on a dup of FD. | |
93 | That way, barring race conditions, fd_clone_opendir returns a | |
94 | stream whose file descriptor is FD. | |
95 | ||
96 | If REPLACE_CHDIR or CWD is null, use opendir ("/proc/self/fd/...", | |
97 | falling back on fchdir metadata. Otherwise, CWD is a saved version | |
98 | of the working directory; use fchdir/opendir(".")/restore_cwd(CWD). */ | |
99 | static DIR * | |
100 | fdopendir_with_dup (int fd, int older_dupfd, struct saved_cwd const *cwd) | |
101 | { | |
102 | int dupfd = dup (fd); | |
103 | if (dupfd < 0 && errno == EMFILE) | |
104 | dupfd = older_dupfd; | |
105 | if (dupfd < 0) | |
106 | return NULL; | |
107 | else | |
108 | { | |
109 | DIR *dir; | |
110 | int saved_errno; | |
111 | if (dupfd < fd - 1 && dupfd != older_dupfd) | |
112 | { | |
113 | dir = fdopendir_with_dup (fd, dupfd, cwd); | |
114 | saved_errno = errno; | |
115 | } | |
116 | else | |
117 | { | |
118 | close (fd); | |
119 | dir = fd_clone_opendir (dupfd, cwd); | |
120 | saved_errno = errno; | |
121 | if (! dir) | |
122 | { | |
123 | int fd1 = dup (dupfd); | |
124 | if (fd1 != fd) | |
125 | openat_save_fail (fd1 < 0 ? errno : EBADF); | |
126 | } | |
127 | } | |
128 | ||
129 | if (dupfd != older_dupfd) | |
130 | close (dupfd); | |
131 | errno = saved_errno; | |
132 | return dir; | |
133 | } | |
134 | } | |
135 | ||
136 | /* Like fdopendir, except the result controls a clone of FD. It is | |
137 | the caller's responsibility both to close FD and (if the result is | |
138 | not null) to closedir the result. */ | |
139 | static DIR * | |
140 | fd_clone_opendir (int fd, struct saved_cwd const *cwd) | |
141 | { | |
142 | if (REPLACE_FCHDIR || ! cwd) | |
143 | { | |
144 | DIR *dir = NULL; | |
145 | int saved_errno = EOPNOTSUPP; | |
146 | char buf[OPENAT_BUFFER_SIZE]; | |
147 | char *proc_file = openat_proc_name (buf, fd, "."); | |
148 | if (proc_file) | |
149 | { | |
150 | dir = opendir (proc_file); | |
151 | saved_errno = errno; | |
152 | if (proc_file != buf) | |
153 | free (proc_file); | |
154 | } | |
155 | # if REPLACE_FCHDIR | |
156 | if (! dir && EXPECTED_ERRNO (saved_errno)) | |
157 | { | |
158 | char const *name = _gl_directory_name (fd); | |
159 | return (name ? opendir (name) : NULL); | |
160 | } | |
161 | # endif | |
162 | errno = saved_errno; | |
163 | return dir; | |
164 | } | |
165 | else | |
166 | { | |
167 | if (fchdir (fd) != 0) | |
168 | return NULL; | |
169 | else | |
170 | { | |
171 | DIR *dir = opendir ("."); | |
172 | int saved_errno = errno; | |
173 | if (restore_cwd (cwd) != 0) | |
174 | openat_restore_fail (errno); | |
175 | errno = saved_errno; | |
176 | return dir; | |
177 | } | |
178 | } | |
179 | } | |
180 | ||
181 | #else /* HAVE_FDOPENDIR */ | |
182 | ||
183 | # include <errno.h> | |
184 | # include <sys/stat.h> | |
185 | ||
186 | # undef fdopendir | |
187 | ||
188 | /* Like fdopendir, but work around GNU/Hurd bug by validating FD. */ | |
189 | ||
190 | DIR * | |
191 | rpl_fdopendir (int fd) | |
192 | { | |
193 | struct stat st; | |
194 | if (fstat (fd, &st)) | |
195 | return NULL; | |
196 | if (!S_ISDIR (st.st_mode)) | |
197 | { | |
198 | errno = ENOTDIR; | |
199 | return NULL; | |
200 | } | |
201 | return fdopendir (fd); | |
202 | } | |
203 | ||
204 | #endif /* HAVE_FDOPENDIR */ |