xref: /freebsd/lib/libc/gen/opendir.c (revision edf8578117e8844e02c0121147f45e4609b30680)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1983, 1993
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  * 3. Neither the name of the University nor the names of its contributors
16  *    may be used to endorse or promote products derived from this software
17  *    without specific prior written permission.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29  * SUCH DAMAGE.
30  */
31 
32 #include <sys/cdefs.h>
33 __SCCSID("@(#)opendir.c	8.8 (Berkeley) 5/1/95");
34 #include "namespace.h"
35 #include <sys/param.h>
36 
37 #include <dirent.h>
38 #include <errno.h>
39 #include <fcntl.h>
40 #include <stdlib.h>
41 #include <string.h>
42 #include <unistd.h>
43 #include "un-namespace.h"
44 
45 #include "gen-private.h"
46 #include "telldir.h"
47 
48 static DIR * __opendir_common(int, int, bool);
49 
50 /*
51  * Open a directory.
52  */
53 DIR *
54 opendir(const char *name)
55 {
56 
57 	return (__opendir2(name, DTF_HIDEW|DTF_NODUP));
58 }
59 
60 /*
61  * Open a directory with existing file descriptor.
62  */
63 DIR *
64 fdopendir(int fd)
65 {
66 
67 	if (_fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
68 		return (NULL);
69 	return (__opendir_common(fd, DTF_HIDEW|DTF_NODUP, true));
70 }
71 
72 DIR *
73 __opendir2(const char *name, int flags)
74 {
75 	int fd;
76 	DIR *dir;
77 	int saved_errno;
78 
79 	if ((flags & (__DTF_READALL | __DTF_SKIPREAD)) != 0)
80 		return (NULL);
81 	if ((fd = _open(name,
82 	    O_RDONLY | O_NONBLOCK | O_DIRECTORY | O_CLOEXEC)) == -1)
83 		return (NULL);
84 
85 	dir = __opendir_common(fd, flags, false);
86 	if (dir == NULL) {
87 		saved_errno = errno;
88 		_close(fd);
89 		errno = saved_errno;
90 	}
91 	return (dir);
92 }
93 
94 static int
95 opendir_compar(const void *p1, const void *p2)
96 {
97 
98 	return (strcmp((*(const struct dirent * const *)p1)->d_name,
99 	    (*(const struct dirent * const *)p2)->d_name));
100 }
101 
102 /*
103  * For a directory at the top of a unionfs stack, the entire directory's
104  * contents are read and cached locally until the next call to rewinddir().
105  * For the fdopendir() case, the initial seek position must be preserved.
106  * For rewinddir(), the full directory should always be re-read from the
107  * beginning.
108  *
109  * If an error occurs, the existing buffer and state of 'dirp' is left
110  * unchanged.
111  */
112 bool
113 _filldir(DIR *dirp, bool use_current_pos)
114 {
115 	struct dirent **dpv;
116 	char *buf, *ddptr, *ddeptr;
117 	off_t pos;
118 	int fd2, incr, len, n, saved_errno, space;
119 
120 	len = 0;
121 	space = 0;
122 	buf = NULL;
123 	ddptr = NULL;
124 
125 	/*
126 	 * Use the system page size if that is a multiple of DIRBLKSIZ.
127 	 * Hopefully this can be a big win someday by allowing page
128 	 * trades to user space to be done by _getdirentries().
129 	 */
130 	incr = getpagesize();
131 	if ((incr % DIRBLKSIZ) != 0)
132 		incr = DIRBLKSIZ;
133 
134 	/*
135 	 * The strategy here is to read all the directory
136 	 * entries into a buffer, sort the buffer, and
137 	 * remove duplicate entries by setting the inode
138 	 * number to zero.
139 	 *
140 	 * We reopen the directory because _getdirentries()
141 	 * on a MNT_UNION mount modifies the open directory,
142 	 * making it refer to the lower directory after the
143 	 * upper directory's entries are exhausted.
144 	 * This would otherwise break software that uses
145 	 * the directory descriptor for fchdir or *at
146 	 * functions, such as fts.c.
147 	 */
148 	if ((fd2 = _openat(dirp->dd_fd, ".", O_RDONLY | O_CLOEXEC)) == -1)
149 		return (false);
150 
151 	if (use_current_pos) {
152 		pos = lseek(dirp->dd_fd, 0, SEEK_CUR);
153 		if (pos == -1 || lseek(fd2, pos, SEEK_SET) == -1) {
154 			saved_errno = errno;
155 			_close(fd2);
156 			errno = saved_errno;
157 			return (false);
158 		}
159 	}
160 
161 	do {
162 		/*
163 		 * Always make at least DIRBLKSIZ bytes
164 		 * available to _getdirentries
165 		 */
166 		if (space < DIRBLKSIZ) {
167 			space += incr;
168 			len += incr;
169 			buf = reallocf(buf, len);
170 			if (buf == NULL) {
171 				saved_errno = errno;
172 				_close(fd2);
173 				errno = saved_errno;
174 				return (false);
175 			}
176 			ddptr = buf + (len - space);
177 		}
178 
179 		n = _getdirentries(fd2, ddptr, space, &dirp->dd_seek);
180 		if (n > 0) {
181 			ddptr += n;
182 			space -= n;
183 		}
184 		if (n < 0) {
185 			saved_errno = errno;
186 			_close(fd2);
187 			errno = saved_errno;
188 			return (false);
189 		}
190 	} while (n > 0);
191 	_close(fd2);
192 
193 	ddeptr = ddptr;
194 
195 	/*
196 	 * There is now a buffer full of (possibly) duplicate
197 	 * names.
198 	 */
199 	dirp->dd_buf = buf;
200 
201 	/*
202 	 * Go round this loop twice...
203 	 *
204 	 * Scan through the buffer, counting entries.
205 	 * On the second pass, save pointers to each one.
206 	 * Then sort the pointers and remove duplicate names.
207 	 */
208 	for (dpv = NULL;;) {
209 		n = 0;
210 		ddptr = buf;
211 		while (ddptr < ddeptr) {
212 			struct dirent *dp;
213 
214 			dp = (struct dirent *) ddptr;
215 			if ((long)dp & 03L)
216 				break;
217 			if ((dp->d_reclen <= 0) ||
218 			    (dp->d_reclen > (ddeptr + 1 - ddptr)))
219 				break;
220 			ddptr += dp->d_reclen;
221 			if (dp->d_fileno) {
222 				if (dpv)
223 					dpv[n] = dp;
224 				n++;
225 			}
226 		}
227 
228 		if (dpv) {
229 			struct dirent *xp;
230 
231 			/*
232 			 * This sort must be stable.
233 			 */
234 			mergesort(dpv, n, sizeof(*dpv), opendir_compar);
235 
236 			dpv[n] = NULL;
237 			xp = NULL;
238 
239 			/*
240 			 * Scan through the buffer in sort order,
241 			 * zapping the inode number of any
242 			 * duplicate names.
243 			 */
244 			for (n = 0; dpv[n]; n++) {
245 				struct dirent *dp = dpv[n];
246 
247 				if ((xp == NULL) ||
248 				    strcmp(dp->d_name, xp->d_name)) {
249 					xp = dp;
250 				} else {
251 					dp->d_fileno = 0;
252 				}
253 				if (dp->d_type == DT_WHT &&
254 				    (dirp->dd_flags & DTF_HIDEW))
255 					dp->d_fileno = 0;
256 			}
257 
258 			free(dpv);
259 			break;
260 		} else {
261 			dpv = malloc((n+1) * sizeof(struct dirent *));
262 			if (dpv == NULL)
263 				break;
264 		}
265 	}
266 
267 	dirp->dd_len = len;
268 	dirp->dd_size = ddptr - dirp->dd_buf;
269 	return (true);
270 }
271 
272 static bool
273 is_unionstack(int fd)
274 {
275 	int unionstack;
276 
277 	unionstack = _fcntl(fd, F_ISUNIONSTACK, 0);
278 	if (unionstack != -1)
279 		return (unionstack);
280 
281 	/*
282 	 * Should not happen unless running on a kernel without the op,
283 	 * but no use rendering the system useless in such a case.
284 	 */
285 	return (0);
286 }
287 
288 /*
289  * Common routine for opendir(3), __opendir2(3) and fdopendir(3).
290  */
291 static DIR *
292 __opendir_common(int fd, int flags, bool use_current_pos)
293 {
294 	DIR *dirp;
295 	int incr;
296 	int saved_errno;
297 	bool unionstack;
298 
299 	if ((dirp = malloc(sizeof(DIR) + sizeof(struct _telldir))) == NULL)
300 		return (NULL);
301 
302 	dirp->dd_buf = NULL;
303 	dirp->dd_fd = fd;
304 	dirp->dd_flags = flags;
305 	dirp->dd_loc = 0;
306 	dirp->dd_lock = NULL;
307 	dirp->dd_td = (struct _telldir *)((char *)dirp + sizeof(DIR));
308 	LIST_INIT(&dirp->dd_td->td_locq);
309 	dirp->dd_td->td_loccnt = 0;
310 	dirp->dd_compat_de = NULL;
311 
312 	/*
313 	 * Use the system page size if that is a multiple of DIRBLKSIZ.
314 	 * Hopefully this can be a big win someday by allowing page
315 	 * trades to user space to be done by _getdirentries().
316 	 */
317 	incr = getpagesize();
318 	if ((incr % DIRBLKSIZ) != 0)
319 		incr = DIRBLKSIZ;
320 
321 	/*
322 	 * Determine whether this directory is the top of a union stack.
323 	 */
324 	unionstack = false;
325 	if (flags & DTF_NODUP) {
326 		unionstack = is_unionstack(fd);
327 	}
328 
329 	if (unionstack) {
330 		if (!_filldir(dirp, use_current_pos))
331 			goto fail;
332 		dirp->dd_flags |= __DTF_READALL;
333 	} else {
334 		dirp->dd_len = incr;
335 		dirp->dd_buf = malloc(dirp->dd_len);
336 		if (dirp->dd_buf == NULL)
337 			goto fail;
338 		if (use_current_pos) {
339 			/*
340 			 * Read the first batch of directory entries
341 			 * to prime dd_seek.  This also checks if the
342 			 * fd passed to fdopendir() is a directory.
343 			 */
344 			dirp->dd_size = _getdirentries(dirp->dd_fd,
345 			    dirp->dd_buf, dirp->dd_len, &dirp->dd_seek);
346 			if (dirp->dd_size < 0) {
347 				if (errno == EINVAL)
348 					errno = ENOTDIR;
349 				goto fail;
350 			}
351 			dirp->dd_flags |= __DTF_SKIPREAD;
352 		} else {
353 			dirp->dd_size = 0;
354 			dirp->dd_seek = 0;
355 		}
356 	}
357 
358 	return (dirp);
359 
360 fail:
361 	saved_errno = errno;
362 	free(dirp->dd_buf);
363 	free(dirp);
364 	errno = saved_errno;
365 	return (NULL);
366 }
367