1 /* provide a replacement openat function
2 Copyright (C) 2004-2022 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 /* If the user's config.h happens to include <fcntl.h>, let it include only
20 the system's <fcntl.h> here, so that orig_openat doesn't recurse to
21 rpl_openat. */
22 #define __need_system_fcntl_h
23 #include <config.h>
24
25 /* Get the original definition of open. It might be defined as a macro. */
26 #include <fcntl.h>
27 #include <sys/types.h>
28 #undef __need_system_fcntl_h
29
30 #if HAVE_OPENAT
31 static int
32 orig_openat (int fd, char const *filename, int flags, mode_t mode)
33 {
34 return openat (fd, filename, flags, mode);
35 }
36 #endif
37
38 /* Write "fcntl.h" here, not <fcntl.h>, otherwise OSF/1 5.1 DTK cc eliminates
39 this include because of the preliminary #include <fcntl.h> above. */
40 #include "fcntl.h"
41
42 #include "openat.h"
43
44 #include "cloexec.h"
45
46 #include <stdarg.h>
47 #include <stdbool.h>
48 #include <stddef.h>
49 #include <stdlib.h>
50 #include <string.h>
51 #include <sys/stat.h>
52 #include <errno.h>
53
54 #if HAVE_OPENAT
55
56 /* Like openat, but support O_CLOEXEC and work around Solaris 9 bugs
57 with trailing slash. */
58 int
59 rpl_openat (int dfd, char const *filename, int flags, ...)
60 {
61 /* 0 = unknown, 1 = yes, -1 = no. */
62 #if GNULIB_defined_O_CLOEXEC
63 int have_cloexec = -1;
64 #else
65 static int have_cloexec;
66 #endif
67
68 mode_t mode;
69 int fd;
70
71 mode = 0;
72 if (flags & O_CREAT)
73 {
74 va_list arg;
75 va_start (arg, flags);
76
77 /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4
78 creates crashing code when 'mode_t' is smaller than 'int'. */
79 mode = va_arg (arg, PROMOTED_MODE_T);
80
81 va_end (arg);
82 }
83
84 # if OPEN_TRAILING_SLASH_BUG
85 /* Fail if one of O_CREAT, O_WRONLY, O_RDWR is specified and the filename
86 ends in a slash, as POSIX says such a filename must name a directory
87 <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
88 "A pathname that contains at least one non-<slash> character and that
89 ends with one or more trailing <slash> characters shall not be resolved
90 successfully unless the last pathname component before the trailing
91 <slash> characters names an existing directory"
92 If the named file already exists as a directory, then
93 - if O_CREAT is specified, open() must fail because of the semantics
94 of O_CREAT,
95 - if O_WRONLY or O_RDWR is specified, open() must fail because POSIX
96 <https://pubs.opengroup.org/onlinepubs/9699919799/functions/openat.html>
97 says that it fails with errno = EISDIR in this case.
98 If the named file does not exist or does not name a directory, then
99 - if O_CREAT is specified, open() must fail since open() cannot create
100 directories,
101 - if O_WRONLY or O_RDWR is specified, open() must fail because the
102 file does not contain a '.' directory. */
103 if ((flags & O_CREAT)
104 || (flags & O_ACCMODE) == O_RDWR
105 || (flags & O_ACCMODE) == O_WRONLY)
106 {
107 size_t len = strlen (filename);
108 if (len > 0 && filename[len - 1] == '/')
109 {
110 errno = EISDIR;
111 return -1;
112 }
113 }
114 # endif
115
116 fd = orig_openat (dfd, filename,
117 flags & ~(have_cloexec < 0 ? O_CLOEXEC : 0), mode);
118
119 if (flags & O_CLOEXEC)
120 {
121 if (! have_cloexec)
122 {
123 if (0 <= fd)
124 have_cloexec = 1;
125 else if (errno == EINVAL)
126 {
127 fd = orig_openat (dfd, filename, flags & ~O_CLOEXEC, mode);
128 have_cloexec = -1;
129 }
130 }
131 if (have_cloexec < 0 && 0 <= fd)
132 set_cloexec_flag (fd, true);
133 }
134
135
136 # if OPEN_TRAILING_SLASH_BUG
137 /* If the filename ends in a slash and fd does not refer to a directory,
138 then fail.
139 Rationale: POSIX says such a filename must name a directory
140 <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
141 "A pathname that contains at least one non-<slash> character and that
142 ends with one or more trailing <slash> characters shall not be resolved
143 successfully unless the last pathname component before the trailing
144 <slash> characters names an existing directory"
145 If the named file without the slash is not a directory, open() must fail
146 with ENOTDIR. */
147 if (fd >= 0)
148 {
149 /* We know len is positive, since open did not fail with ENOENT. */
150 size_t len = strlen (filename);
151 if (filename[len - 1] == '/')
152 {
153 struct stat statbuf;
154
155 if (fstat (fd, &statbuf) >= 0 && !S_ISDIR (statbuf.st_mode))
156 {
157 close (fd);
158 errno = ENOTDIR;
159 return -1;
160 }
161 }
162 }
163 # endif
164
165 return fd;
166 }
167
168 #else /* !HAVE_OPENAT */
169
170 # include "filename.h" /* solely for definition of IS_ABSOLUTE_FILE_NAME */
171 # include "openat-priv.h"
172 # include "save-cwd.h"
173
174 /* Replacement for Solaris' openat function.
175 <https://www.google.com/search?q=openat+site:docs.oracle.com>
176 First, try to simulate it via open ("/proc/self/fd/FD/FILE").
177 Failing that, simulate it by doing save_cwd/fchdir/open/restore_cwd.
178 If either the save_cwd or the restore_cwd fails (relatively unlikely),
179 then give a diagnostic and exit nonzero.
180 Otherwise, upon failure, set errno and return -1, as openat does.
181 Upon successful completion, return a file descriptor. */
182 int
183 openat (int fd, char const *file, int flags, ...)
184 {
185 mode_t mode = 0;
186
187 if (flags & O_CREAT)
188 {
189 va_list arg;
190 va_start (arg, flags);
191
192 /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4
193 creates crashing code when 'mode_t' is smaller than 'int'. */
194 mode = va_arg (arg, PROMOTED_MODE_T);
195
196 va_end (arg);
197 }
198
199 return openat_permissive (fd, file, flags, mode, NULL);
200 }
201
202 /* Like openat (FD, FILE, FLAGS, MODE), but if CWD_ERRNO is
203 nonnull, set *CWD_ERRNO to an errno value if unable to save
204 or restore the initial working directory. This is needed only
205 the first time remove.c's remove_dir opens a command-line
206 directory argument.
207
208 If a previous attempt to restore the current working directory
209 failed, then we must not even try to access a '.'-relative name.
210 It is the caller's responsibility not to call this function
211 in that case. */
212
213 int
214 openat_permissive (int fd, char const *file, int flags, mode_t mode,
215 int *cwd_errno)
216 {
217 struct saved_cwd saved_cwd;
218 int saved_errno;
219 int err;
220 bool save_ok;
221
222 if (fd == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file))
223 return open (file, flags, mode);
224
225 {
226 char buf[OPENAT_BUFFER_SIZE];
227 char *proc_file = openat_proc_name (buf, fd, file);
228 if (proc_file)
229 {
230 int open_result = open (proc_file, flags, mode);
231 int open_errno = errno;
232 if (proc_file != buf)
233 free (proc_file);
234 /* If the syscall succeeds, or if it fails with an unexpected
235 errno value, then return right away. Otherwise, fall through
236 and resort to using save_cwd/restore_cwd. */
237 if (0 <= open_result || ! EXPECTED_ERRNO (open_errno))
238 {
239 errno = open_errno;
240 return open_result;
241 }
242 }
243 }
244
245 save_ok = (save_cwd (&saved_cwd) == 0);
246 if (! save_ok)
247 {
248 if (! cwd_errno)
249 openat_save_fail (errno);
250 *cwd_errno = errno;
251 }
252 if (0 <= fd && fd == saved_cwd.desc)
253 {
254 /* If saving the working directory collides with the user's
255 requested fd, then the user's fd must have been closed to
256 begin with. */
257 free_cwd (&saved_cwd);
258 errno = EBADF;
259 return -1;
260 }
261
262 err = fchdir (fd);
263 saved_errno = errno;
264
265 if (! err)
266 {
267 err = open (file, flags, mode);
268 saved_errno = errno;
269 if (save_ok && restore_cwd (&saved_cwd) != 0)
270 {
271 if (! cwd_errno)
272 {
273 /* Don't write a message to just-created fd 2. */
274 saved_errno = errno;
275 if (err == STDERR_FILENO)
276 close (err);
277 openat_restore_fail (saved_errno);
278 }
279 *cwd_errno = errno;
280 }
281 }
282
283 free_cwd (&saved_cwd);
284 errno = saved_errno;
285 return err;
286 }
287
288 /* Return true if our openat implementation must resort to
289 using save_cwd and restore_cwd. */
290 bool
291 openat_needs_fchdir (void)
292 {
293 bool needs_fchdir = true;
294 int fd = open ("/", O_SEARCH | O_CLOEXEC);
295
296 if (0 <= fd)
297 {
298 char buf[OPENAT_BUFFER_SIZE];
299 char *proc_file = openat_proc_name (buf, fd, ".");
300 if (proc_file)
301 {
302 needs_fchdir = false;
303 if (proc_file != buf)
304 free (proc_file);
305 }
306 close (fd);
307 }
308
309 return needs_fchdir;
310 }
311
312 #endif /* !HAVE_OPENAT */