1/* Copyright (C) 2002-2021 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <errno.h>
20#include <fcntl.h>
21#include <pthread.h>
22#include <search.h>
23#include <semaphore.h>
24#include <stdarg.h>
25#include <stdio.h>
26#include <stdlib.h>
27#include <string.h>
28#include <unistd.h>
29#include <sys/mman.h>
30#include <sys/stat.h>
31#include "semaphoreP.h"
32#include <shm-directory.h>
33#include <futex-internal.h>
34#include <libc-lock.h>
35
36/* Comparison function for search of existing mapping. */
37int
38attribute_hidden
39__sem_search (const void *a, const void *b)
40{
41 const struct inuse_sem *as = (const struct inuse_sem *) a;
42 const struct inuse_sem *bs = (const struct inuse_sem *) b;
43
44 if (as->ino != bs->ino)
45 /* Cannot return the difference the type is larger than int. */
46 return as->ino < bs->ino ? -1 : (as->ino == bs->ino ? 0 : 1);
47
48 if (as->dev != bs->dev)
49 /* Cannot return the difference the type is larger than int. */
50 return as->dev < bs->dev ? -1 : (as->dev == bs->dev ? 0 : 1);
51
52 return strcmp (as->name, bs->name);
53}
54
55
56/* The search tree for existing mappings. */
57void *__sem_mappings attribute_hidden;
58
59/* Lock to protect the search tree. */
60int __sem_mappings_lock attribute_hidden = LLL_LOCK_INITIALIZER;
61
62
63/* Search for existing mapping and if possible add the one provided. */
64static sem_t *
65check_add_mapping (const char *name, size_t namelen, int fd, sem_t *existing)
66{
67 sem_t *result = SEM_FAILED;
68
69 /* Get the information about the file. */
70 struct stat64 st;
71 if (__fstat64 (fd, &st) == 0)
72 {
73 /* Get the lock. */
74 lll_lock (__sem_mappings_lock, LLL_PRIVATE);
75
76 /* Search for an existing mapping given the information we have. */
77 struct inuse_sem *fake;
78 fake = (struct inuse_sem *) alloca (sizeof (*fake) + namelen);
79 memcpy (fake->name, name, namelen);
80 fake->dev = st.st_dev;
81 fake->ino = st.st_ino;
82
83 struct inuse_sem **foundp = __tfind (fake, &__sem_mappings,
84 __sem_search);
85 if (foundp != NULL)
86 {
87 /* There is already a mapping. Use it. */
88 result = (*foundp)->sem;
89 ++(*foundp)->refcnt;
90 }
91 else
92 {
93 /* We haven't found a mapping. Install ione. */
94 struct inuse_sem *newp;
95
96 newp = (struct inuse_sem *) malloc (sizeof (*newp) + namelen);
97 if (newp != NULL)
98 {
99 /* If the caller hasn't provided any map it now. */
100 if (existing == SEM_FAILED)
101 existing = (sem_t *) mmap (NULL, sizeof (sem_t),
102 PROT_READ | PROT_WRITE, MAP_SHARED,
103 fd, 0);
104
105 newp->dev = st.st_dev;
106 newp->ino = st.st_ino;
107 newp->refcnt = 1;
108 newp->sem = existing;
109 memcpy (newp->name, name, namelen);
110
111 /* Insert the new value. */
112 if (existing != MAP_FAILED
113 && __tsearch (newp, &__sem_mappings, __sem_search) != NULL)
114 /* Successful. */
115 result = existing;
116 else
117 /* Something went wrong while inserting the new
118 value. We fail completely. */
119 free (newp);
120 }
121 }
122
123 /* Release the lock. */
124 lll_unlock (__sem_mappings_lock, LLL_PRIVATE);
125 }
126
127 if (result != existing && existing != SEM_FAILED && existing != MAP_FAILED)
128 {
129 /* Do not disturb errno. */
130 int save = errno;
131 munmap (existing, sizeof (sem_t));
132 errno = save;
133 }
134
135 return result;
136}
137
138
139sem_t *
140sem_open (const char *name, int oflag, ...)
141{
142 int fd;
143 sem_t *result;
144
145 /* Check that shared futexes are supported. */
146 int err = futex_supports_pshared (PTHREAD_PROCESS_SHARED);
147 if (err != 0)
148 {
149 __set_errno (err);
150 return SEM_FAILED;
151 }
152
153 /* Create the name of the final file in local variable SHM_NAME. */
154 SHM_GET_NAME (EINVAL, SEM_FAILED, SEM_SHM_PREFIX);
155
156 /* Disable asynchronous cancellation. */
157#ifdef __libc_ptf_call
158 int state;
159 __libc_ptf_call (__pthread_setcancelstate,
160 (PTHREAD_CANCEL_DISABLE, &state), 0);
161#endif
162
163 /* If the semaphore object has to exist simply open it. */
164 if ((oflag & O_CREAT) == 0 || (oflag & O_EXCL) == 0)
165 {
166 try_again:
167 fd = __libc_open (shm_name,
168 (oflag & ~(O_CREAT|O_ACCMODE)) | O_NOFOLLOW | O_RDWR);
169
170 if (fd == -1)
171 {
172 /* If we are supposed to create the file try this next. */
173 if ((oflag & O_CREAT) != 0 && errno == ENOENT)
174 goto try_create;
175
176 /* Return. errno is already set. */
177 }
178 else
179 /* Check whether we already have this semaphore mapped and
180 create one if necessary. */
181 result = check_add_mapping (name, namelen, fd, SEM_FAILED);
182 }
183 else
184 {
185 /* We have to open a temporary file first since it must have the
186 correct form before we can start using it. */
187 char *tmpfname;
188 mode_t mode;
189 unsigned int value;
190 va_list ap;
191
192 try_create:
193 va_start (ap, oflag);
194
195 mode = va_arg (ap, mode_t);
196 value = va_arg (ap, unsigned int);
197
198 va_end (ap);
199
200 if (value > SEM_VALUE_MAX)
201 {
202 __set_errno (EINVAL);
203 result = SEM_FAILED;
204 goto out;
205 }
206
207 /* Create the initial file content. */
208 union
209 {
210 sem_t initsem;
211 struct new_sem newsem;
212 } sem;
213
214 __new_sem_open_init (&sem.newsem, value);
215
216 /* Initialize the remaining bytes as well. */
217 memset ((char *) &sem.initsem + sizeof (struct new_sem), '\0',
218 sizeof (sem_t) - sizeof (struct new_sem));
219
220 tmpfname = __alloca (shm_dirlen + sizeof SEM_SHM_PREFIX + 6);
221 char *xxxxxx = __mempcpy (tmpfname, shm_dir, shm_dirlen);
222
223 int retries = 0;
224#define NRETRIES 50
225 while (1)
226 {
227 /* Add the suffix for mktemp. */
228 strcpy (xxxxxx, "XXXXXX");
229
230 /* We really want to use mktemp here. We cannot use mkstemp
231 since the file must be opened with a specific mode. The
232 mode cannot later be set since then we cannot apply the
233 file create mask. */
234 if (__mktemp (tmpfname) == NULL)
235 {
236 result = SEM_FAILED;
237 goto out;
238 }
239
240 /* Open the file. Make sure we do not overwrite anything. */
241 fd = __libc_open (tmpfname, O_RDWR | O_CREAT | O_EXCL, mode);
242 if (fd == -1)
243 {
244 if (errno == EEXIST)
245 {
246 if (++retries < NRETRIES)
247 continue;
248
249 __set_errno (EAGAIN);
250 }
251
252 result = SEM_FAILED;
253 goto out;
254 }
255
256 /* We got a file. */
257 break;
258 }
259
260 if (TEMP_FAILURE_RETRY (__libc_write (fd, &sem.initsem, sizeof (sem_t)))
261 == sizeof (sem_t)
262 /* Map the sem_t structure from the file. */
263 && (result = (sem_t *) mmap (NULL, sizeof (sem_t),
264 PROT_READ | PROT_WRITE, MAP_SHARED,
265 fd, 0)) != MAP_FAILED)
266 {
267 /* Create the file. Don't overwrite an existing file. */
268 if (link (tmpfname, shm_name) != 0)
269 {
270 /* Undo the mapping. */
271 (void) munmap (result, sizeof (sem_t));
272
273 /* Reinitialize 'result'. */
274 result = SEM_FAILED;
275
276 /* This failed. If O_EXCL is not set and the problem was
277 that the file exists, try again. */
278 if ((oflag & O_EXCL) == 0 && errno == EEXIST)
279 {
280 /* Remove the file. */
281 (void) unlink (tmpfname);
282
283 /* Close the file. */
284 (void) __libc_close (fd);
285
286 goto try_again;
287 }
288 }
289 else
290 /* Insert the mapping into the search tree. This also
291 determines whether another thread sneaked by and already
292 added such a mapping despite the fact that we created it. */
293 result = check_add_mapping (name, namelen, fd, result);
294 }
295
296 /* Now remove the temporary name. This should never fail. If
297 it fails we leak a file name. Better fix the kernel. */
298 (void) unlink (tmpfname);
299 }
300
301 /* Map the mmap error to the error we need. */
302 if (MAP_FAILED != (void *) SEM_FAILED && result == MAP_FAILED)
303 result = SEM_FAILED;
304
305 /* We don't need the file descriptor anymore. */
306 if (fd != -1)
307 {
308 /* Do not disturb errno. */
309 int save = errno;
310 __libc_close (fd);
311 errno = save;
312 }
313
314out:
315#ifdef __libc_ptf_call
316 __libc_ptf_call (__pthread_setcancelstate, (state, NULL), 0);
317#endif
318
319 return result;
320}
321