xref: /freebsd/lib/libc/gen/opendir.c (revision a0b9e2e854027e6ff61fb075a1309dbc71c42b54)
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 __FBSDID("$FreeBSD$");
35 
36 #include "namespace.h"
37 #include <sys/param.h>
38 
39 #include <dirent.h>
40 #include <errno.h>
41 #include <fcntl.h>
42 #include <stdlib.h>
43 #include <string.h>
44 #include <unistd.h>
45 #include "un-namespace.h"
46 
47 #include "gen-private.h"
48 #include "telldir.h"
49 
50 static DIR * __opendir_common(int, int, bool);
51 
52 /*
53  * Open a directory.
54  */
55 DIR *
56 opendir(const char *name)
57 {
58 
59 	return (__opendir2(name, DTF_HIDEW|DTF_NODUP));
60 }
61 
62 /*
63  * Open a directory with existing file descriptor.
64  */
65 DIR *
66 fdopendir(int fd)
67 {
68 
69 	if (_fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
70 		return (NULL);
71 	return (__opendir_common(fd, DTF_HIDEW|DTF_NODUP, true));
72 }
73 
74 DIR *
75 __opendir2(const char *name, int flags)
76 {
77 	int fd;
78 	DIR *dir;
79 	int saved_errno;
80 
81 	if ((flags & (__DTF_READALL | __DTF_SKIPREAD)) != 0)
82 		return (NULL);
83 	if ((fd = _open(name,
84 	    O_RDONLY | O_NONBLOCK | O_DIRECTORY | O_CLOEXEC)) == -1)
85 		return (NULL);
86 
87 	dir = __opendir_common(fd, flags, false);
88 	if (dir == NULL) {
89 		saved_errno = errno;
90 		_close(fd);
91 		errno = saved_errno;
92 	}
93 	return (dir);
94 }
95 
96 static int
97 opendir_compar(const void *p1, const void *p2)
98 {
99 
100 	return (strcmp((*(const struct dirent * const *)p1)->d_name,
101 	    (*(const struct dirent * const *)p2)->d_name));
102 }
103 
104 /*
105  * For a directory at the top of a unionfs stack, the entire directory's
106  * contents are read and cached locally until the next call to rewinddir().
107  * For the fdopendir() case, the initial seek position must be preserved.
108  * For rewinddir(), the full directory should always be re-read from the
109  * beginning.
110  *
111  * If an error occurs, the existing buffer and state of 'dirp' is left
112  * unchanged.
113  */
114 bool
115 _filldir(DIR *dirp, bool use_current_pos)
116 {
117 	struct dirent **dpv;
118 	char *buf, *ddptr, *ddeptr;
119 	off_t pos;
120 	int fd2, incr, len, n, saved_errno, space;
121 
122 	len = 0;
123 	space = 0;
124 	buf = NULL;
125 	ddptr = NULL;
126 
127 	/*
128 	 * Use the system page size if that is a multiple of DIRBLKSIZ.
129 	 * Hopefully this can be a big win someday by allowing page
130 	 * trades to user space to be done by _getdirentries().
131 	 */
132 	incr = getpagesize();
133 	if ((incr % DIRBLKSIZ) != 0)
134 		incr = DIRBLKSIZ;
135 
136 	/*
137 	 * The strategy here is to read all the directory
138 	 * entries into a buffer, sort the buffer, and
139 	 * remove duplicate entries by setting the inode
140 	 * number to zero.
141 	 *
142 	 * We reopen the directory because _getdirentries()
143 	 * on a MNT_UNION mount modifies the open directory,
144 	 * making it refer to the lower directory after the
145 	 * upper directory's entries are exhausted.
146 	 * This would otherwise break software that uses
147 	 * the directory descriptor for fchdir or *at
148 	 * functions, such as fts.c.
149 	 */
150 	if ((fd2 = _openat(dirp->dd_fd, ".", O_RDONLY | O_CLOEXEC)) == -1)
151 		return (false);
152 
153 	if (use_current_pos) {
154 		pos = lseek(dirp->dd_fd, 0, SEEK_CUR);
155 		if (pos == -1 || lseek(fd2, pos, SEEK_SET) == -1) {
156 			saved_errno = errno;
157 			_close(fd2);
158 			errno = saved_errno;
159 			return (false);
160 		}
161 	}
162 
163 	do {
164 		/*
165 		 * Always make at least DIRBLKSIZ bytes
166 		 * available to _getdirentries
167 		 */
168 		if (space < DIRBLKSIZ) {
169 			space += incr;
170 			len += incr;
171 			buf = reallocf(buf, len);
172 			if (buf == NULL) {
173 				saved_errno = errno;
174 				_close(fd2);
175 				errno = saved_errno;
176 				return (false);
177 			}
178 			ddptr = buf + (len - space);
179 		}
180 
181 		n = _getdirentries(fd2, ddptr, space, &dirp->dd_seek);
182 		if (n > 0) {
183 			ddptr += n;
184 			space -= n;
185 		}
186 		if (n < 0) {
187 			saved_errno = errno;
188 			_close(fd2);
189 			errno = saved_errno;
190 			return (false);
191 		}
192 	} while (n > 0);
193 	_close(fd2);
194 
195 	ddeptr = ddptr;
196 
197 	/*
198 	 * There is now a buffer full of (possibly) duplicate
199 	 * names.
200 	 */
201 	dirp->dd_buf = buf;
202 
203 	/*
204 	 * Go round this loop twice...
205 	 *
206 	 * Scan through the buffer, counting entries.
207 	 * On the second pass, save pointers to each one.
208 	 * Then sort the pointers and remove duplicate names.
209 	 */
210 	for (dpv = NULL;;) {
211 		n = 0;
212 		ddptr = buf;
213 		while (ddptr < ddeptr) {
214 			struct dirent *dp;
215 
216 			dp = (struct dirent *) ddptr;
217 			if ((long)dp & 03L)
218 				break;
219 			if ((dp->d_reclen <= 0) ||
220 			    (dp->d_reclen > (ddeptr + 1 - ddptr)))
221 				break;
222 			ddptr += dp->d_reclen;
223 			if (dp->d_fileno) {
224 				if (dpv)
225 					dpv[n] = dp;
226 				n++;
227 			}
228 		}
229 
230 		if (dpv) {
231 			struct dirent *xp;
232 
233 			/*
234 			 * This sort must be stable.
235 			 */
236 			mergesort(dpv, n, sizeof(*dpv), opendir_compar);
237 
238 			dpv[n] = NULL;
239 			xp = NULL;
240 
241 			/*
242 			 * Scan through the buffer in sort order,
243 			 * zapping the inode number of any
244 			 * duplicate names.
245 			 */
246 			for (n = 0; dpv[n]; n++) {
247 				struct dirent *dp = dpv[n];
248 
249 				if ((xp == NULL) ||
250 				    strcmp(dp->d_name, xp->d_name)) {
251 					xp = dp;
252 				} else {
253 					dp->d_fileno = 0;
254 				}
255 				if (dp->d_type == DT_WHT &&
256 				    (dirp->dd_flags & DTF_HIDEW))
257 					dp->d_fileno = 0;
258 			}
259 
260 			free(dpv);
261 			break;
262 		} else {
263 			dpv = malloc((n+1) * sizeof(struct dirent *));
264 			if (dpv == NULL)
265 				break;
266 		}
267 	}
268 
269 	dirp->dd_len = len;
270 	dirp->dd_size = ddptr - dirp->dd_buf;
271 	return (true);
272 }
273 
274 static bool
275 is_unionstack(int fd)
276 {
277 	int unionstack;
278 
279 	unionstack = _fcntl(fd, F_ISUNIONSTACK, 0);
280 	if (unionstack != -1)
281 		return (unionstack);
282 
283 	/*
284 	 * Should not happen unless running on a kernel without the op,
285 	 * but no use rendering the system useless in such a case.
286 	 */
287 	return (0);
288 }
289 
290 /*
291  * Common routine for opendir(3), __opendir2(3) and fdopendir(3).
292  */
293 static DIR *
294 __opendir_common(int fd, int flags, bool use_current_pos)
295 {
296 	DIR *dirp;
297 	int incr;
298 	int saved_errno;
299 	bool unionstack;
300 
301 	if ((dirp = malloc(sizeof(DIR) + sizeof(struct _telldir))) == NULL)
302 		return (NULL);
303 
304 	dirp->dd_buf = NULL;
305 	dirp->dd_fd = fd;
306 	dirp->dd_flags = flags;
307 	dirp->dd_loc = 0;
308 	dirp->dd_lock = NULL;
309 	dirp->dd_td = (struct _telldir *)((char *)dirp + sizeof(DIR));
310 	LIST_INIT(&dirp->dd_td->td_locq);
311 	dirp->dd_td->td_loccnt = 0;
312 	dirp->dd_compat_de = NULL;
313 
314 	/*
315 	 * Use the system page size if that is a multiple of DIRBLKSIZ.
316 	 * Hopefully this can be a big win someday by allowing page
317 	 * trades to user space to be done by _getdirentries().
318 	 */
319 	incr = getpagesize();
320 	if ((incr % DIRBLKSIZ) != 0)
321 		incr = DIRBLKSIZ;
322 
323 	/*
324 	 * Determine whether this directory is the top of a union stack.
325 	 */
326 	unionstack = false;
327 	if (flags & DTF_NODUP) {
328 		unionstack = is_unionstack(fd);
329 	}
330 
331 	if (unionstack) {
332 		if (!_filldir(dirp, use_current_pos))
333 			goto fail;
334 		dirp->dd_flags |= __DTF_READALL;
335 	} else {
336 		dirp->dd_len = incr;
337 		dirp->dd_buf = malloc(dirp->dd_len);
338 		if (dirp->dd_buf == NULL)
339 			goto fail;
340 		if (use_current_pos) {
341 			/*
342 			 * Read the first batch of directory entries
343 			 * to prime dd_seek.  This also checks if the
344 			 * fd passed to fdopendir() is a directory.
345 			 */
346 			dirp->dd_size = _getdirentries(dirp->dd_fd,
347 			    dirp->dd_buf, dirp->dd_len, &dirp->dd_seek);
348 			if (dirp->dd_size < 0) {
349 				if (errno == EINVAL)
350 					errno = ENOTDIR;
351 				goto fail;
352 			}
353 			dirp->dd_flags |= __DTF_SKIPREAD;
354 		} else {
355 			dirp->dd_size = 0;
356 			dirp->dd_seek = 0;
357 		}
358 	}
359 
360 	return (dirp);
361 
362 fail:
363 	saved_errno = errno;
364 	free(dirp->dd_buf);
365 	free(dirp);
366 	errno = saved_errno;
367 	return (NULL);
368 }
369