FreeBSD/Linux Kernel Cross Reference
sys/kern/uipc_shm.c
1 /*-
2 * Copyright (c) 2006 Robert N. M. Watson
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27 /*
28 * Support for shared swap-backed anonymous memory objects via
29 * shm_open(2) and shm_unlink(2). While most of the implementation is
30 * here, vm_mmap.c contains mapping logic changes.
31 *
32 * TODO:
33 *
34 * (2) Need to export data to a userland tool via a sysctl. Should ipcs(1)
35 * and ipcrm(1) be expanded or should new tools to manage both POSIX
36 * kernel semaphores and POSIX shared memory be written?
37 *
38 * (3) Add support for this file type to fstat(1).
39 *
40 * (4) Resource limits? Does this need its own resource limits or are the
41 * existing limits in mmap(2) sufficient?
42 *
43 * (5) Partial page truncation. vnode_pager_setsize() will zero any parts
44 * of a partially mapped page as a result of ftruncate(2)/truncate(2).
45 * We can do the same (with the same pmap evil), but do we need to
46 * worry about the bits on disk if the page is swapped out or will the
47 * swapper zero the parts of a page that are invalid if the page is
48 * swapped back in for us?
49 *
50 * (6) Add MAC support in mac_biba(4) and mac_mls(4).
51 *
52 * (7) Add a MAC check_create() hook for creating new named objects.
53 */
54
55 #include <sys/cdefs.h>
56 __FBSDID("$FreeBSD: releng/8.3/sys/kern/uipc_shm.c 199583 2009-11-20 15:27:52Z jhb $");
57
58 #include <sys/param.h>
59 #include <sys/fcntl.h>
60 #include <sys/file.h>
61 #include <sys/filedesc.h>
62 #include <sys/fnv_hash.h>
63 #include <sys/kernel.h>
64 #include <sys/lock.h>
65 #include <sys/malloc.h>
66 #include <sys/mman.h>
67 #include <sys/mutex.h>
68 #include <sys/proc.h>
69 #include <sys/refcount.h>
70 #include <sys/resourcevar.h>
71 #include <sys/stat.h>
72 #include <sys/sysctl.h>
73 #include <sys/sysproto.h>
74 #include <sys/systm.h>
75 #include <sys/sx.h>
76 #include <sys/time.h>
77 #include <sys/vnode.h>
78
79 #include <security/mac/mac_framework.h>
80
81 #include <vm/vm.h>
82 #include <vm/vm_param.h>
83 #include <vm/pmap.h>
84 #include <vm/vm_map.h>
85 #include <vm/vm_object.h>
86 #include <vm/vm_page.h>
87 #include <vm/vm_pager.h>
88 #include <vm/swap_pager.h>
89
90 struct shm_mapping {
91 char *sm_path;
92 Fnv32_t sm_fnv;
93 struct shmfd *sm_shmfd;
94 LIST_ENTRY(shm_mapping) sm_link;
95 };
96
97 static MALLOC_DEFINE(M_SHMFD, "shmfd", "shared memory file descriptor");
98 static LIST_HEAD(, shm_mapping) *shm_dictionary;
99 static struct sx shm_dict_lock;
100 static struct mtx shm_timestamp_lock;
101 static u_long shm_hash;
102
103 #define SHM_HASH(fnv) (&shm_dictionary[(fnv) & shm_hash])
104
105 static int shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags);
106 static struct shmfd *shm_alloc(struct ucred *ucred, mode_t mode);
107 static void shm_dict_init(void *arg);
108 static void shm_drop(struct shmfd *shmfd);
109 static struct shmfd *shm_hold(struct shmfd *shmfd);
110 static void shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd);
111 static struct shmfd *shm_lookup(char *path, Fnv32_t fnv);
112 static int shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred);
113 static int shm_dotruncate(struct shmfd *shmfd, off_t length);
114
115 static fo_rdwr_t shm_read;
116 static fo_rdwr_t shm_write;
117 static fo_truncate_t shm_truncate;
118 static fo_ioctl_t shm_ioctl;
119 static fo_poll_t shm_poll;
120 static fo_kqfilter_t shm_kqfilter;
121 static fo_stat_t shm_stat;
122 static fo_close_t shm_close;
123
124 /* File descriptor operations. */
125 static struct fileops shm_ops = {
126 .fo_read = shm_read,
127 .fo_write = shm_write,
128 .fo_truncate = shm_truncate,
129 .fo_ioctl = shm_ioctl,
130 .fo_poll = shm_poll,
131 .fo_kqfilter = shm_kqfilter,
132 .fo_stat = shm_stat,
133 .fo_close = shm_close,
134 .fo_flags = DFLAG_PASSABLE
135 };
136
137 FEATURE(posix_shm, "POSIX shared memory");
138
139 static int
140 shm_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
141 int flags, struct thread *td)
142 {
143
144 return (EOPNOTSUPP);
145 }
146
147 static int
148 shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
149 int flags, struct thread *td)
150 {
151
152 return (EOPNOTSUPP);
153 }
154
155 static int
156 shm_truncate(struct file *fp, off_t length, struct ucred *active_cred,
157 struct thread *td)
158 {
159 struct shmfd *shmfd;
160 #ifdef MAC
161 int error;
162 #endif
163
164 shmfd = fp->f_data;
165 #ifdef MAC
166 error = mac_posixshm_check_truncate(active_cred, fp->f_cred, shmfd);
167 if (error)
168 return (error);
169 #endif
170 return (shm_dotruncate(shmfd, length));
171 }
172
173 static int
174 shm_ioctl(struct file *fp, u_long com, void *data,
175 struct ucred *active_cred, struct thread *td)
176 {
177
178 return (EOPNOTSUPP);
179 }
180
181 static int
182 shm_poll(struct file *fp, int events, struct ucred *active_cred,
183 struct thread *td)
184 {
185
186 return (EOPNOTSUPP);
187 }
188
189 static int
190 shm_kqfilter(struct file *fp, struct knote *kn)
191 {
192
193 return (EOPNOTSUPP);
194 }
195
196 static int
197 shm_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
198 struct thread *td)
199 {
200 struct shmfd *shmfd;
201 #ifdef MAC
202 int error;
203 #endif
204
205 shmfd = fp->f_data;
206
207 #ifdef MAC
208 error = mac_posixshm_check_stat(active_cred, fp->f_cred, shmfd);
209 if (error)
210 return (error);
211 #endif
212
213 /*
214 * Attempt to return sanish values for fstat() on a memory file
215 * descriptor.
216 */
217 bzero(sb, sizeof(*sb));
218 sb->st_mode = S_IFREG | shmfd->shm_mode; /* XXX */
219 sb->st_blksize = PAGE_SIZE;
220 sb->st_size = shmfd->shm_size;
221 sb->st_blocks = (sb->st_size + sb->st_blksize - 1) / sb->st_blksize;
222 sb->st_atimespec = shmfd->shm_atime;
223 sb->st_ctimespec = shmfd->shm_ctime;
224 sb->st_mtimespec = shmfd->shm_mtime;
225 sb->st_birthtimespec = shmfd->shm_birthtime;
226 sb->st_uid = shmfd->shm_uid;
227 sb->st_gid = shmfd->shm_gid;
228
229 return (0);
230 }
231
232 static int
233 shm_close(struct file *fp, struct thread *td)
234 {
235 struct shmfd *shmfd;
236
237 shmfd = fp->f_data;
238 fp->f_data = NULL;
239 shm_drop(shmfd);
240
241 return (0);
242 }
243
244 static int
245 shm_dotruncate(struct shmfd *shmfd, off_t length)
246 {
247 vm_object_t object;
248 vm_page_t m;
249 vm_pindex_t nobjsize;
250 vm_ooffset_t delta;
251
252 object = shmfd->shm_object;
253 VM_OBJECT_LOCK(object);
254 if (length == shmfd->shm_size) {
255 VM_OBJECT_UNLOCK(object);
256 return (0);
257 }
258 nobjsize = OFF_TO_IDX(length + PAGE_MASK);
259
260 /* Are we shrinking? If so, trim the end. */
261 if (length < shmfd->shm_size) {
262 delta = ptoa(object->size - nobjsize);
263
264 /* Toss in memory pages. */
265 if (nobjsize < object->size)
266 vm_object_page_remove(object, nobjsize, object->size,
267 FALSE);
268
269 /* Toss pages from swap. */
270 if (object->type == OBJT_SWAP)
271 swap_pager_freespace(object, nobjsize, delta);
272
273 /* Free the swap accounted for shm */
274 swap_release_by_uid(delta, object->uip);
275 object->charge -= delta;
276
277 /*
278 * If the last page is partially mapped, then zero out
279 * the garbage at the end of the page. See comments
280 * in vnode_pager_setsize() for more details.
281 *
282 * XXXJHB: This handles in memory pages, but what about
283 * a page swapped out to disk?
284 */
285 if ((length & PAGE_MASK) &&
286 (m = vm_page_lookup(object, OFF_TO_IDX(length))) != NULL &&
287 m->valid != 0) {
288 int base = (int)length & PAGE_MASK;
289 int size = PAGE_SIZE - base;
290
291 pmap_zero_page_area(m, base, size);
292
293 /*
294 * Update the valid bits to reflect the blocks that
295 * have been zeroed. Some of these valid bits may
296 * have already been set.
297 */
298 vm_page_set_valid(m, base, size);
299
300 /*
301 * Round "base" to the next block boundary so that the
302 * dirty bit for a partially zeroed block is not
303 * cleared.
304 */
305 base = roundup2(base, DEV_BSIZE);
306
307 vm_page_lock_queues();
308 vm_page_clear_dirty(m, base, PAGE_SIZE - base);
309 vm_page_unlock_queues();
310 } else if ((length & PAGE_MASK) &&
311 __predict_false(object->cache != NULL)) {
312 vm_page_cache_free(object, OFF_TO_IDX(length),
313 nobjsize);
314 }
315 } else {
316
317 /* Attempt to reserve the swap */
318 delta = ptoa(nobjsize - object->size);
319 if (!swap_reserve_by_uid(delta, object->uip)) {
320 VM_OBJECT_UNLOCK(object);
321 return (ENOMEM);
322 }
323 object->charge += delta;
324 }
325 shmfd->shm_size = length;
326 mtx_lock(&shm_timestamp_lock);
327 vfs_timestamp(&shmfd->shm_ctime);
328 shmfd->shm_mtime = shmfd->shm_ctime;
329 mtx_unlock(&shm_timestamp_lock);
330 object->size = nobjsize;
331 VM_OBJECT_UNLOCK(object);
332 return (0);
333 }
334
335 /*
336 * shmfd object management including creation and reference counting
337 * routines.
338 */
339 static struct shmfd *
340 shm_alloc(struct ucred *ucred, mode_t mode)
341 {
342 struct shmfd *shmfd;
343
344 shmfd = malloc(sizeof(*shmfd), M_SHMFD, M_WAITOK | M_ZERO);
345 shmfd->shm_size = 0;
346 shmfd->shm_uid = ucred->cr_uid;
347 shmfd->shm_gid = ucred->cr_gid;
348 shmfd->shm_mode = mode;
349 shmfd->shm_object = vm_pager_allocate(OBJT_DEFAULT, NULL,
350 shmfd->shm_size, VM_PROT_DEFAULT, 0, ucred);
351 KASSERT(shmfd->shm_object != NULL, ("shm_create: vm_pager_allocate"));
352 VM_OBJECT_LOCK(shmfd->shm_object);
353 vm_object_clear_flag(shmfd->shm_object, OBJ_ONEMAPPING);
354 vm_object_set_flag(shmfd->shm_object, OBJ_NOSPLIT);
355 VM_OBJECT_UNLOCK(shmfd->shm_object);
356 vfs_timestamp(&shmfd->shm_birthtime);
357 shmfd->shm_atime = shmfd->shm_mtime = shmfd->shm_ctime =
358 shmfd->shm_birthtime;
359 refcount_init(&shmfd->shm_refs, 1);
360 #ifdef MAC
361 mac_posixshm_init(shmfd);
362 mac_posixshm_create(ucred, shmfd);
363 #endif
364
365 return (shmfd);
366 }
367
368 static struct shmfd *
369 shm_hold(struct shmfd *shmfd)
370 {
371
372 refcount_acquire(&shmfd->shm_refs);
373 return (shmfd);
374 }
375
376 static void
377 shm_drop(struct shmfd *shmfd)
378 {
379
380 if (refcount_release(&shmfd->shm_refs)) {
381 #ifdef MAC
382 mac_posixshm_destroy(shmfd);
383 #endif
384 vm_object_deallocate(shmfd->shm_object);
385 free(shmfd, M_SHMFD);
386 }
387 }
388
389 /*
390 * Determine if the credentials have sufficient permissions for a
391 * specified combination of FREAD and FWRITE.
392 */
393 static int
394 shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags)
395 {
396 accmode_t accmode;
397
398 accmode = 0;
399 if (flags & FREAD)
400 accmode |= VREAD;
401 if (flags & FWRITE)
402 accmode |= VWRITE;
403 return (vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid, shmfd->shm_gid,
404 accmode, ucred, NULL));
405 }
406
407 /*
408 * Dictionary management. We maintain an in-kernel dictionary to map
409 * paths to shmfd objects. We use the FNV hash on the path to store
410 * the mappings in a hash table.
411 */
412 static void
413 shm_dict_init(void *arg)
414 {
415
416 mtx_init(&shm_timestamp_lock, "shm timestamps", NULL, MTX_DEF);
417 sx_init(&shm_dict_lock, "shm dictionary");
418 shm_dictionary = hashinit(1024, M_SHMFD, &shm_hash);
419 }
420 SYSINIT(shm_dict_init, SI_SUB_SYSV_SHM, SI_ORDER_ANY, shm_dict_init, NULL);
421
422 static struct shmfd *
423 shm_lookup(char *path, Fnv32_t fnv)
424 {
425 struct shm_mapping *map;
426
427 LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
428 if (map->sm_fnv != fnv)
429 continue;
430 if (strcmp(map->sm_path, path) == 0)
431 return (map->sm_shmfd);
432 }
433
434 return (NULL);
435 }
436
437 static void
438 shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd)
439 {
440 struct shm_mapping *map;
441
442 map = malloc(sizeof(struct shm_mapping), M_SHMFD, M_WAITOK);
443 map->sm_path = path;
444 map->sm_fnv = fnv;
445 map->sm_shmfd = shm_hold(shmfd);
446 LIST_INSERT_HEAD(SHM_HASH(fnv), map, sm_link);
447 }
448
449 static int
450 shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred)
451 {
452 struct shm_mapping *map;
453 int error;
454
455 LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
456 if (map->sm_fnv != fnv)
457 continue;
458 if (strcmp(map->sm_path, path) == 0) {
459 #ifdef MAC
460 error = mac_posixshm_check_unlink(ucred, map->sm_shmfd);
461 if (error)
462 return (error);
463 #endif
464 error = shm_access(map->sm_shmfd, ucred,
465 FREAD | FWRITE);
466 if (error)
467 return (error);
468 LIST_REMOVE(map, sm_link);
469 shm_drop(map->sm_shmfd);
470 free(map->sm_path, M_SHMFD);
471 free(map, M_SHMFD);
472 return (0);
473 }
474 }
475
476 return (ENOENT);
477 }
478
479 /* System calls. */
480 int
481 shm_open(struct thread *td, struct shm_open_args *uap)
482 {
483 struct filedesc *fdp;
484 struct shmfd *shmfd;
485 struct file *fp;
486 char *path;
487 Fnv32_t fnv;
488 mode_t cmode;
489 int fd, error;
490
491 if ((uap->flags & O_ACCMODE) != O_RDONLY &&
492 (uap->flags & O_ACCMODE) != O_RDWR)
493 return (EINVAL);
494
495 if ((uap->flags & ~(O_ACCMODE | O_CREAT | O_EXCL | O_TRUNC)) != 0)
496 return (EINVAL);
497
498 fdp = td->td_proc->p_fd;
499 cmode = (uap->mode & ~fdp->fd_cmask) & ACCESSPERMS;
500
501 error = falloc(td, &fp, &fd);
502 if (error)
503 return (error);
504
505 /* A SHM_ANON path pointer creates an anonymous object. */
506 if (uap->path == SHM_ANON) {
507 /* A read-only anonymous object is pointless. */
508 if ((uap->flags & O_ACCMODE) == O_RDONLY) {
509 fdclose(fdp, fp, fd, td);
510 fdrop(fp, td);
511 return (EINVAL);
512 }
513 shmfd = shm_alloc(td->td_ucred, cmode);
514 } else {
515 path = malloc(MAXPATHLEN, M_SHMFD, M_WAITOK);
516 error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
517
518 /* Require paths to start with a '/' character. */
519 if (error == 0 && path[0] != '/')
520 error = EINVAL;
521 if (error) {
522 fdclose(fdp, fp, fd, td);
523 fdrop(fp, td);
524 free(path, M_SHMFD);
525 return (error);
526 }
527
528 fnv = fnv_32_str(path, FNV1_32_INIT);
529 sx_xlock(&shm_dict_lock);
530 shmfd = shm_lookup(path, fnv);
531 if (shmfd == NULL) {
532 /* Object does not yet exist, create it if requested. */
533 if (uap->flags & O_CREAT) {
534 shmfd = shm_alloc(td->td_ucred, cmode);
535 shm_insert(path, fnv, shmfd);
536 } else {
537 free(path, M_SHMFD);
538 error = ENOENT;
539 }
540 } else {
541 /*
542 * Object already exists, obtain a new
543 * reference if requested and permitted.
544 */
545 free(path, M_SHMFD);
546 if ((uap->flags & (O_CREAT | O_EXCL)) ==
547 (O_CREAT | O_EXCL))
548 error = EEXIST;
549 else {
550 #ifdef MAC
551 error = mac_posixshm_check_open(td->td_ucred,
552 shmfd);
553 if (error == 0)
554 #endif
555 error = shm_access(shmfd, td->td_ucred,
556 FFLAGS(uap->flags & O_ACCMODE));
557 }
558
559 /*
560 * Truncate the file back to zero length if
561 * O_TRUNC was specified and the object was
562 * opened with read/write.
563 */
564 if (error == 0 &&
565 (uap->flags & (O_ACCMODE | O_TRUNC)) ==
566 (O_RDWR | O_TRUNC)) {
567 #ifdef MAC
568 error = mac_posixshm_check_truncate(
569 td->td_ucred, fp->f_cred, shmfd);
570 if (error == 0)
571 #endif
572 shm_dotruncate(shmfd, 0);
573 }
574 if (error == 0)
575 shm_hold(shmfd);
576 }
577 sx_xunlock(&shm_dict_lock);
578
579 if (error) {
580 fdclose(fdp, fp, fd, td);
581 fdrop(fp, td);
582 return (error);
583 }
584 }
585
586 finit(fp, FFLAGS(uap->flags & O_ACCMODE), DTYPE_SHM, shmfd, &shm_ops);
587
588 FILEDESC_XLOCK(fdp);
589 if (fdp->fd_ofiles[fd] == fp)
590 fdp->fd_ofileflags[fd] |= UF_EXCLOSE;
591 FILEDESC_XUNLOCK(fdp);
592 td->td_retval[0] = fd;
593 fdrop(fp, td);
594
595 return (0);
596 }
597
598 int
599 shm_unlink(struct thread *td, struct shm_unlink_args *uap)
600 {
601 char *path;
602 Fnv32_t fnv;
603 int error;
604
605 path = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
606 error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
607 if (error) {
608 free(path, M_TEMP);
609 return (error);
610 }
611
612 fnv = fnv_32_str(path, FNV1_32_INIT);
613 sx_xlock(&shm_dict_lock);
614 error = shm_remove(path, fnv, td->td_ucred);
615 sx_xunlock(&shm_dict_lock);
616 free(path, M_TEMP);
617
618 return (error);
619 }
620
621 /*
622 * mmap() helper to validate mmap() requests against shm object state
623 * and give mmap() the vm_object to use for the mapping.
624 */
625 int
626 shm_mmap(struct shmfd *shmfd, vm_size_t objsize, vm_ooffset_t foff,
627 vm_object_t *obj)
628 {
629
630 /*
631 * XXXRW: This validation is probably insufficient, and subject to
632 * sign errors. It should be fixed.
633 */
634 if (foff >= shmfd->shm_size ||
635 foff + objsize > round_page(shmfd->shm_size))
636 return (EINVAL);
637
638 mtx_lock(&shm_timestamp_lock);
639 vfs_timestamp(&shmfd->shm_atime);
640 mtx_unlock(&shm_timestamp_lock);
641 vm_object_reference(shmfd->shm_object);
642 *obj = shmfd->shm_object;
643 return (0);
644 }
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