1 | /* Copyright (C) 1991-2017 Free Software Foundation, Inc. |
2 | This file is part of the GNU C Library. |
3 | |
4 | The GNU C Library is free software; you can redistribute it and/or |
5 | modify it under the terms of the GNU Lesser General Public |
6 | License as published by the Free Software Foundation; either |
7 | version 2.1 of the License, or (at your option) any later version. |
8 | |
9 | The GNU C Library 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 GNU |
12 | Lesser General Public License for more details. |
13 | |
14 | You should have received a copy of the GNU Lesser General Public |
15 | License along with the GNU C Library; if not, see |
16 | <http://www.gnu.org/licenses/>. */ |
17 | |
18 | #include <assert.h> |
19 | #include <errno.h> |
20 | #include <limits.h> |
21 | #include <stdbool.h> |
22 | #include <stddef.h> |
23 | #include <stdlib.h> |
24 | #include <dirent.h> |
25 | #include <fcntl.h> |
26 | #include <sys/param.h> |
27 | #include <sys/types.h> |
28 | #include <sys/stat.h> |
29 | #include <unistd.h> |
30 | #include <stdio.h> |
31 | #include <string.h> |
32 | |
33 | #include <dirstream.h> |
34 | #include <not-cancel.h> |
35 | #include <kernel-features.h> |
36 | |
37 | /* The st_blksize value of the directory is used as a hint for the |
38 | size of the buffer which receives struct dirent values from the |
39 | kernel. st_blksize is limited to MAX_DIR_BUFFER_SIZE, in case the |
40 | file system provides a bogus value. */ |
41 | #define MAX_DIR_BUFFER_SIZE 1048576U |
42 | |
43 | /* opendir() must not accidentally open something other than a directory. |
44 | Some OS's have kernel support for that, some don't. In the worst |
45 | case we have to stat() before the open() AND fstat() after. |
46 | |
47 | We have to test at runtime for kernel support since libc may have |
48 | been compiled with different headers to the kernel it's running on. |
49 | This test can't be done reliably in the general case. We'll use |
50 | /dev/null, which if it's not a device lots of stuff will break, as |
51 | a guinea pig. It may be missing in chroot environments, so we |
52 | make sure to fail safe. */ |
53 | #ifdef O_DIRECTORY |
54 | # ifdef O_DIRECTORY_WORKS |
55 | # define o_directory_works 1 |
56 | # define tryopen_o_directory() while (1) /* This must not be called. */ |
57 | # else |
58 | static int o_directory_works; |
59 | |
60 | static void |
61 | tryopen_o_directory (void) |
62 | { |
63 | int serrno = errno; |
64 | int x = open_not_cancel_2 ("/dev/null" , O_RDONLY|O_NDELAY|O_DIRECTORY); |
65 | |
66 | if (x >= 0) |
67 | { |
68 | close_not_cancel_no_status (x); |
69 | o_directory_works = -1; |
70 | } |
71 | else if (errno != ENOTDIR) |
72 | o_directory_works = -1; |
73 | else |
74 | o_directory_works = 1; |
75 | |
76 | __set_errno (serrno); |
77 | } |
78 | # endif |
79 | # define O_DIRECTORY |
80 | #else |
81 | # define EXTRA_FLAGS 0 |
82 | #endif |
83 | |
84 | |
85 | static bool |
86 | invalid_name (const char *name) |
87 | { |
88 | if (__glibc_unlikely (name[0] == '\0')) |
89 | { |
90 | /* POSIX.1-1990 says an empty name gets ENOENT; |
91 | but `open' might like it fine. */ |
92 | __set_errno (ENOENT); |
93 | return true; |
94 | } |
95 | return false; |
96 | } |
97 | |
98 | |
99 | static bool |
100 | need_isdir_precheck (void) |
101 | { |
102 | #ifdef O_DIRECTORY |
103 | /* Test whether O_DIRECTORY works. */ |
104 | if (o_directory_works == 0) |
105 | tryopen_o_directory (); |
106 | |
107 | /* We can skip the expensive `stat' call if O_DIRECTORY works. */ |
108 | return o_directory_works < 0; |
109 | #endif |
110 | return true; |
111 | } |
112 | |
113 | |
114 | static int |
115 | opendir_oflags (void) |
116 | { |
117 | int flags = O_RDONLY|O_NDELAY|EXTRA_FLAGS|O_LARGEFILE; |
118 | #ifdef O_CLOEXEC |
119 | flags |= O_CLOEXEC; |
120 | #endif |
121 | return flags; |
122 | } |
123 | |
124 | |
125 | static DIR * |
126 | opendir_tail (int fd) |
127 | { |
128 | if (__glibc_unlikely (fd < 0)) |
129 | return NULL; |
130 | |
131 | /* Now make sure this really is a directory and nothing changed since the |
132 | `stat' call. The S_ISDIR check is superfluous if O_DIRECTORY works, |
133 | but it's cheap and we need the stat call for st_blksize anyway. */ |
134 | struct stat64 statbuf; |
135 | if (__glibc_unlikely (__fxstat64 (_STAT_VER, fd, &statbuf) < 0)) |
136 | goto lose; |
137 | if (__glibc_unlikely (! S_ISDIR (statbuf.st_mode))) |
138 | { |
139 | __set_errno (ENOTDIR); |
140 | lose: |
141 | close_not_cancel_no_status (fd); |
142 | return NULL; |
143 | } |
144 | |
145 | return __alloc_dir (fd, true, 0, &statbuf); |
146 | } |
147 | |
148 | |
149 | #if IS_IN (libc) |
150 | DIR * |
151 | internal_function |
152 | __opendirat (int dfd, const char *name) |
153 | { |
154 | if (__glibc_unlikely (invalid_name (name))) |
155 | return NULL; |
156 | |
157 | if (need_isdir_precheck ()) |
158 | { |
159 | /* We first have to check whether the name is for a directory. We |
160 | cannot do this after the open() call since the open/close operation |
161 | performed on, say, a tape device might have undesirable effects. */ |
162 | struct stat64 statbuf; |
163 | if (__glibc_unlikely (__fxstatat64 (_STAT_VER, dfd, name, |
164 | &statbuf, 0) < 0)) |
165 | return NULL; |
166 | if (__glibc_unlikely (! S_ISDIR (statbuf.st_mode))) |
167 | { |
168 | __set_errno (ENOTDIR); |
169 | return NULL; |
170 | } |
171 | } |
172 | |
173 | return opendir_tail (openat_not_cancel_3 (dfd, name, opendir_oflags ())); |
174 | } |
175 | #endif |
176 | |
177 | |
178 | /* Open a directory stream on NAME. */ |
179 | DIR * |
180 | __opendir (const char *name) |
181 | { |
182 | if (__glibc_unlikely (invalid_name (name))) |
183 | return NULL; |
184 | |
185 | if (need_isdir_precheck ()) |
186 | { |
187 | /* We first have to check whether the name is for a directory. We |
188 | cannot do this after the open() call since the open/close operation |
189 | performed on, say, a tape device might have undesirable effects. */ |
190 | struct stat64 statbuf; |
191 | if (__glibc_unlikely (__xstat64 (_STAT_VER, name, &statbuf) < 0)) |
192 | return NULL; |
193 | if (__glibc_unlikely (! S_ISDIR (statbuf.st_mode))) |
194 | { |
195 | __set_errno (ENOTDIR); |
196 | return NULL; |
197 | } |
198 | } |
199 | |
200 | return opendir_tail (open_not_cancel_2 (name, opendir_oflags ())); |
201 | } |
202 | weak_alias (__opendir, opendir) |
203 | |
204 | |
205 | #ifdef __ASSUME_O_CLOEXEC |
206 | # define check_have_o_cloexec(fd) 1 |
207 | #else |
208 | static int |
209 | check_have_o_cloexec (int fd) |
210 | { |
211 | if (__have_o_cloexec == 0) |
212 | __have_o_cloexec = (__fcntl (fd, F_GETFD, 0) & FD_CLOEXEC) == 0 ? -1 : 1; |
213 | return __have_o_cloexec > 0; |
214 | } |
215 | #endif |
216 | |
217 | |
218 | DIR * |
219 | internal_function |
220 | __alloc_dir (int fd, bool close_fd, int flags, const struct stat64 *statp) |
221 | { |
222 | /* We always have to set the close-on-exit flag if the user provided |
223 | the file descriptor. Otherwise only if we have no working |
224 | O_CLOEXEC support. */ |
225 | #ifdef O_CLOEXEC |
226 | if ((! close_fd && (flags & O_CLOEXEC) == 0) |
227 | || ! check_have_o_cloexec (fd)) |
228 | #endif |
229 | { |
230 | if (__builtin_expect (__fcntl (fd, F_SETFD, FD_CLOEXEC), 0) < 0) |
231 | goto lose; |
232 | } |
233 | |
234 | const size_t default_allocation = (4 * BUFSIZ < sizeof (struct dirent64) |
235 | ? sizeof (struct dirent64) : 4 * BUFSIZ); |
236 | const size_t small_allocation = (BUFSIZ < sizeof (struct dirent64) |
237 | ? sizeof (struct dirent64) : BUFSIZ); |
238 | size_t allocation = default_allocation; |
239 | #ifdef _STATBUF_ST_BLKSIZE |
240 | /* Increase allocation if requested, but not if the value appears to |
241 | be bogus. */ |
242 | if (statp != NULL) |
243 | allocation = MIN (MAX ((size_t) statp->st_blksize, default_allocation), |
244 | MAX_DIR_BUFFER_SIZE); |
245 | #endif |
246 | |
247 | DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation); |
248 | if (dirp == NULL) |
249 | { |
250 | allocation = small_allocation; |
251 | dirp = (DIR *) malloc (sizeof (DIR) + allocation); |
252 | |
253 | if (dirp == NULL) |
254 | lose: |
255 | { |
256 | if (close_fd) |
257 | { |
258 | int save_errno = errno; |
259 | close_not_cancel_no_status (fd); |
260 | __set_errno (save_errno); |
261 | } |
262 | return NULL; |
263 | } |
264 | } |
265 | |
266 | dirp->fd = fd; |
267 | #if IS_IN (libc) |
268 | __libc_lock_init (dirp->lock); |
269 | #endif |
270 | dirp->allocation = allocation; |
271 | dirp->size = 0; |
272 | dirp->offset = 0; |
273 | dirp->filepos = 0; |
274 | dirp->errcode = 0; |
275 | |
276 | return dirp; |
277 | } |
278 | |