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("$FreeBSD$");
  57
  58 #include "opt_mac.h"
  59
  60 #include <sys/param.h>
  61 #include <sys/fcntl.h>
  62 #include <sys/file.h>
  63 #include <sys/filedesc.h>
  64 #include <sys/fnv_hash.h>
  65 #include <sys/kernel.h>
  66 #include <sys/lock.h>
  67 #include <sys/malloc.h>
  68 #include <sys/mman.h>
  69 #include <sys/mutex.h>
  70 #include <sys/proc.h>
  71 #include <sys/refcount.h>
  72 #include <sys/resourcevar.h>
  73 #include <sys/stat.h>
  74 #include <sys/sysctl.h>
  75 #include <sys/sysproto.h>
  76 #include <sys/systm.h>
  77 #include <sys/sx.h>
  78 #include <sys/time.h>
  79 #include <sys/vnode.h>
  80
  81 #include <security/mac/mac_framework.h>
  82
  83 #include <vm/vm.h>
  84 #include <vm/vm_param.h>
  85 #include <vm/pmap.h>
  86 #include <vm/vm_map.h>
  87 #include <vm/vm_object.h>
  88 #include <vm/vm_page.h>
  89 #include <vm/vm_pager.h>
  90 #include <vm/swap_pager.h>
  91
  92 struct shm_mapping {
  93         char            *sm_path;
  94         Fnv32_t         sm_fnv;
  95         struct shmfd    *sm_shmfd;
  96         LIST_ENTRY(shm_mapping) sm_link;
  97 };
  98
  99 static MALLOC_DEFINE(M_SHMFD, "shmfd", "shared memory file descriptor");
 100 static LIST_HEAD(, shm_mapping) *shm_dictionary;
 101 static struct sx shm_dict_lock;
 102 static struct mtx shm_timestamp_lock;
 103 static u_long shm_hash;
 104
 105 #define SHM_HASH(fnv)   (&shm_dictionary[(fnv) & shm_hash])
 106
 107 static int      shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags);
 108 static struct shmfd *shm_alloc(struct ucred *ucred, mode_t mode);
 109 static void     shm_dict_init(void *arg);
 110 static void     shm_drop(struct shmfd *shmfd);
 111 static struct shmfd *shm_hold(struct shmfd *shmfd);
 112 static void     shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd);
 113 static struct shmfd *shm_lookup(char *path, Fnv32_t fnv);
 114 static int      shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred);
 115 static void     shm_dotruncate(struct shmfd *shmfd, off_t length);
 116
 117 static fo_rdwr_t        shm_read;
 118 static fo_rdwr_t        shm_write;
 119 static fo_truncate_t    shm_truncate;
 120 static fo_ioctl_t       shm_ioctl;
 121 static fo_poll_t        shm_poll;
 122 static fo_kqfilter_t    shm_kqfilter;
 123 static fo_stat_t        shm_stat;
 124 static fo_close_t       shm_close;
 125
 126 /* File descriptor operations. */
 127 static struct fileops shm_ops = {
 128         .fo_read = shm_read,
 129         .fo_write = shm_write,
 130         .fo_truncate = shm_truncate,
 131         .fo_ioctl = shm_ioctl,
 132         .fo_poll = shm_poll,
 133         .fo_kqfilter = shm_kqfilter,
 134         .fo_stat = shm_stat,
 135         .fo_close = shm_close,
 136         .fo_flags = DFLAG_PASSABLE
 137 };
 138
 139 FEATURE(posix_shm, "POSIX shared memory");
 140
 141 static int
 142 shm_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
 143     int flags, struct thread *td)
 144 {
 145
 146         return (EOPNOTSUPP);
 147 }
 148
 149 static int
 150 shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
 151     int flags, struct thread *td)
 152 {
 153
 154         return (EOPNOTSUPP);
 155 }
 156
 157 static int
 158 shm_truncate(struct file *fp, off_t length, struct ucred *active_cred,
 159     struct thread *td)
 160 {
 161         struct shmfd *shmfd;
 162 #ifdef MAC
 163         int error;
 164 #endif
 165
 166         shmfd = fp->f_data;
 167 #ifdef MAC
 168         error = mac_posixshm_check_truncate(active_cred, fp->f_cred, shmfd);
 169         if (error)
 170                 return (error);
 171 #endif
 172         shm_dotruncate(shmfd, length);
 173         return (0);
 174 }
 175
 176 static int
 177 shm_ioctl(struct file *fp, u_long com, void *data,
 178     struct ucred *active_cred, struct thread *td)
 179 {
 180
 181         return (EOPNOTSUPP);
 182 }
 183
 184 static int
 185 shm_poll(struct file *fp, int events, struct ucred *active_cred,
 186     struct thread *td)
 187 {
 188
 189         return (EOPNOTSUPP);
 190 }
 191
 192 static int
 193 shm_kqfilter(struct file *fp, struct knote *kn)
 194 {
 195
 196         return (EOPNOTSUPP);
 197 }
 198
 199 static int
 200 shm_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
 201     struct thread *td)
 202 {
 203         struct shmfd *shmfd;
 204 #ifdef MAC
 205         int error;
 206 #endif
 207
 208         shmfd = fp->f_data;
 209
 210 #ifdef MAC
 211         error = mac_posixshm_check_stat(active_cred, fp->f_cred, shmfd);
 212         if (error)
 213                 return (error);
 214 #endif
 215
 216         /*
 217          * Attempt to return sanish values for fstat() on a memory file
 218          * descriptor.
 219          */
 220         bzero(sb, sizeof(*sb));
 221         sb->st_mode = S_IFREG | shmfd->shm_mode;                /* XXX */
 222         sb->st_blksize = PAGE_SIZE;
 223         sb->st_size = shmfd->shm_size;
 224         sb->st_blocks = (sb->st_size + sb->st_blksize - 1) / sb->st_blksize;
 225         sb->st_atimespec = shmfd->shm_atime;
 226         sb->st_ctimespec = shmfd->shm_ctime;
 227         sb->st_mtimespec = shmfd->shm_mtime;
 228         sb->st_birthtimespec = shmfd->shm_birthtime;
 229         sb->st_uid = shmfd->shm_uid;
 230         sb->st_gid = shmfd->shm_gid;
 231
 232         return (0);
 233 }
 234
 235 static int
 236 shm_close(struct file *fp, struct thread *td)
 237 {
 238         struct shmfd *shmfd;
 239
 240         shmfd = fp->f_data;
 241         fp->f_data = NULL;
 242         shm_drop(shmfd);
 243
 244         return (0);
 245 }
 246
 247 static void
 248 shm_dotruncate(struct shmfd *shmfd, off_t length)
 249 {
 250         vm_object_t object;
 251         vm_page_t m;
 252         vm_pindex_t nobjsize;
 253
 254         object = shmfd->shm_object;
 255         VM_OBJECT_LOCK(object);
 256         if (length == shmfd->shm_size) {
 257                 VM_OBJECT_UNLOCK(object);
 258                 return;
 259         }
 260         nobjsize = OFF_TO_IDX(length + PAGE_MASK);
 261
 262         /* Are we shrinking?  If so, trim the end. */
 263         if (length < shmfd->shm_size) {
 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,
 272                             object->size - nobjsize);
 273
 274                 /*
 275                  * If the last page is partially mapped, then zero out
 276                  * the garbage at the end of the page.  See comments
 277                  * in vnode_page_setsize() for more details.
 278                  *
 279                  * XXXJHB: This handles in memory pages, but what about
 280                  * a page swapped out to disk?
 281                  */
 282                 if ((length & PAGE_MASK) &&
 283                     (m = vm_page_lookup(object, OFF_TO_IDX(length))) != NULL &&
 284                     m->valid != 0) {
 285                         int base = (int)length & PAGE_MASK;
 286                         int size = PAGE_SIZE - base;
 287
 288                         pmap_zero_page_area(m, base, size);
 289                         vm_page_lock_queues();
 290                         vm_page_set_validclean(m, base, size);
 291                         if (m->dirty != 0)
 292                                 m->dirty = VM_PAGE_BITS_ALL;
 293                         vm_page_unlock_queues();
 294                 } else if ((length & PAGE_MASK) &&
 295                     __predict_false(object->cache != NULL)) {
 296                         vm_page_cache_free(object, OFF_TO_IDX(length),
 297                             nobjsize);
 298                 }
 299         }
 300         shmfd->shm_size = length;
 301         mtx_lock(&shm_timestamp_lock);
 302         vfs_timestamp(&shmfd->shm_ctime);
 303         shmfd->shm_mtime = shmfd->shm_ctime;
 304         mtx_unlock(&shm_timestamp_lock);
 305         object->size = nobjsize;
 306         VM_OBJECT_UNLOCK(object);
 307 }
 308
 309 /*
 310  * shmfd object management including creation and reference counting
 311  * routines.
 312  */
 313 static struct shmfd *
 314 shm_alloc(struct ucred *ucred, mode_t mode)
 315 {
 316         struct shmfd *shmfd;
 317
 318         shmfd = malloc(sizeof(*shmfd), M_SHMFD, M_WAITOK | M_ZERO);
 319         shmfd->shm_size = 0;
 320         shmfd->shm_uid = ucred->cr_uid;
 321         shmfd->shm_gid = ucred->cr_gid;
 322         shmfd->shm_mode = mode;
 323         shmfd->shm_object = vm_pager_allocate(OBJT_DEFAULT, NULL,
 324             shmfd->shm_size, VM_PROT_DEFAULT, 0);
 325         KASSERT(shmfd->shm_object != NULL, ("shm_create: vm_pager_allocate"));
 326         VM_OBJECT_LOCK(shmfd->shm_object);
 327         vm_object_clear_flag(shmfd->shm_object, OBJ_ONEMAPPING);
 328         vm_object_set_flag(shmfd->shm_object, OBJ_NOSPLIT);
 329         VM_OBJECT_UNLOCK(shmfd->shm_object);
 330         vfs_timestamp(&shmfd->shm_birthtime);
 331         shmfd->shm_atime = shmfd->shm_mtime = shmfd->shm_ctime =
 332             shmfd->shm_birthtime;
 333         refcount_init(&shmfd->shm_refs, 1);
 334 #ifdef MAC
 335         mac_posixshm_init(shmfd);
 336         mac_posixshm_create(ucred, shmfd);
 337 #endif
 338
 339         return (shmfd);
 340 }
 341
 342 static struct shmfd *
 343 shm_hold(struct shmfd *shmfd)
 344 {
 345
 346         refcount_acquire(&shmfd->shm_refs);
 347         return (shmfd);
 348 }
 349
 350 static void
 351 shm_drop(struct shmfd *shmfd)
 352 {
 353
 354         if (refcount_release(&shmfd->shm_refs)) {
 355 #ifdef MAC
 356                 mac_posixshm_destroy(shmfd);
 357 #endif
 358                 vm_object_deallocate(shmfd->shm_object);
 359                 free(shmfd, M_SHMFD);
 360         }
 361 }
 362
 363 /*
 364  * Determine if the credentials have sufficient permissions for a
 365  * specified combination of FREAD and FWRITE.
 366  */
 367 static int
 368 shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags)
 369 {
 370         int acc_mode;
 371
 372         acc_mode = 0;
 373         if (flags & FREAD)
 374                 acc_mode |= VREAD;
 375         if (flags & FWRITE)
 376                 acc_mode |= VWRITE;
 377         return (vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid, shmfd->shm_gid,
 378             acc_mode, ucred, NULL));
 379 }
 380
 381 /*
 382  * Dictionary management.  We maintain an in-kernel dictionary to map
 383  * paths to shmfd objects.  We use the FNV hash on the path to store
 384  * the mappings in a hash table.
 385  */
 386 static void
 387 shm_dict_init(void *arg)
 388 {
 389
 390         mtx_init(&shm_timestamp_lock, "shm timestamps", NULL, MTX_DEF);
 391         sx_init(&shm_dict_lock, "shm dictionary");
 392         shm_dictionary = hashinit(1024, M_SHMFD, &shm_hash);
 393 }
 394 SYSINIT(shm_dict_init, SI_SUB_SYSV_SHM, SI_ORDER_ANY, shm_dict_init, NULL);
 395
 396 static struct shmfd *
 397 shm_lookup(char *path, Fnv32_t fnv)
 398 {
 399         struct shm_mapping *map;
 400
 401         LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
 402                 if (map->sm_fnv != fnv)
 403                         continue;
 404                 if (strcmp(map->sm_path, path) == 0)
 405                         return (map->sm_shmfd);
 406         }
 407
 408         return (NULL);
 409 }
 410
 411 static void
 412 shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd)
 413 {
 414         struct shm_mapping *map;
 415
 416         map = malloc(sizeof(struct shm_mapping), M_SHMFD, M_WAITOK);
 417         map->sm_path = path;
 418         map->sm_fnv = fnv;
 419         map->sm_shmfd = shm_hold(shmfd);
 420         LIST_INSERT_HEAD(SHM_HASH(fnv), map, sm_link);
 421 }
 422
 423 static int
 424 shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred)
 425 {
 426         struct shm_mapping *map;
 427         int error;
 428
 429         LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
 430                 if (map->sm_fnv != fnv)
 431                         continue;
 432                 if (strcmp(map->sm_path, path) == 0) {
 433 #ifdef MAC
 434                         error = mac_posixshm_check_unlink(ucred, map->sm_shmfd);
 435                         if (error)
 436                                 return (error);
 437 #endif
 438                         error = shm_access(map->sm_shmfd, ucred,
 439                             FREAD | FWRITE);
 440                         if (error)
 441                                 return (error);
 442                         LIST_REMOVE(map, sm_link);
 443                         shm_drop(map->sm_shmfd);
 444                         free(map->sm_path, M_SHMFD);
 445                         free(map, M_SHMFD);
 446                         return (0);
 447                 }
 448         }
 449
 450         return (ENOENT);
 451 }
 452
 453 /* System calls. */
 454 int
 455 shm_open(struct thread *td, struct shm_open_args *uap)
 456 {
 457         struct filedesc *fdp;
 458         struct shmfd *shmfd;
 459         struct file *fp;
 460         char *path;
 461         Fnv32_t fnv;
 462         mode_t cmode;
 463         int fd, error;
 464
 465         if ((uap->flags & O_ACCMODE) != O_RDONLY &&
 466             (uap->flags & O_ACCMODE) != O_RDWR)
 467                 return (EINVAL);
 468
 469         if ((uap->flags & ~(O_ACCMODE | O_CREAT | O_EXCL | O_TRUNC)) != 0)
 470                 return (EINVAL);
 471
 472         fdp = td->td_proc->p_fd;
 473         cmode = (uap->mode & ~fdp->fd_cmask) & ACCESSPERMS;
 474
 475         error = falloc(td, &fp, &fd);
 476         if (error)
 477                 return (error);
 478
 479         /* A SHM_ANON path pointer creates an anonymous object. */
 480         if (uap->path == SHM_ANON) {
 481                 /* A read-only anonymous object is pointless. */
 482                 if ((uap->flags & O_ACCMODE) == O_RDONLY) {
 483                         fdclose(fdp, fp, fd, td);
 484                         fdrop(fp, td);
 485                         return (EINVAL);
 486                 }
 487                 shmfd = shm_alloc(td->td_ucred, cmode);
 488         } else {
 489                 path = malloc(MAXPATHLEN, M_SHMFD, M_WAITOK);
 490                 error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
 491
 492                 /* Require paths to start with a '/' character. */
 493                 if (error == 0 && path[0] != '/')
 494                         error = EINVAL;
 495                 if (error) {
 496                         fdclose(fdp, fp, fd, td);
 497                         fdrop(fp, td);
 498                         free(path, M_SHMFD);
 499                         return (error);
 500                 }
 501
 502                 fnv = fnv_32_str(path, FNV1_32_INIT);
 503                 sx_xlock(&shm_dict_lock);
 504                 shmfd = shm_lookup(path, fnv);
 505                 if (shmfd == NULL) {
 506                         /* Object does not yet exist, create it if requested. */
 507                         if (uap->flags & O_CREAT) {
 508                                 shmfd = shm_alloc(td->td_ucred, cmode);
 509                                 shm_insert(path, fnv, shmfd);
 510                         } else {
 511                                 free(path, M_SHMFD);
 512                                 error = ENOENT;
 513                         }
 514                 } else {
 515                         /*
 516                          * Object already exists, obtain a new
 517                          * reference if requested and permitted.
 518                          */
 519                         free(path, M_SHMFD);
 520                         if ((uap->flags & (O_CREAT | O_EXCL)) ==
 521                             (O_CREAT | O_EXCL))
 522                                 error = EEXIST;
 523                         else {
 524 #ifdef MAC
 525                                 error = mac_posixshm_check_open(td->td_ucred,
 526                                     shmfd);
 527                                 if (error == 0)
 528 #endif
 529                                 error = shm_access(shmfd, td->td_ucred,
 530                                     FFLAGS(uap->flags & O_ACCMODE));
 531                         }
 532
 533                         /*
 534                          * Truncate the file back to zero length if
 535                          * O_TRUNC was specified and the object was
 536                          * opened with read/write.
 537                          */
 538                         if (error == 0 &&
 539                             (uap->flags & (O_ACCMODE | O_TRUNC)) ==
 540                             (O_RDWR | O_TRUNC)) {
 541 #ifdef MAC
 542                                 error = mac_posixshm_check_truncate(
 543                                         td->td_ucred, fp->f_cred, shmfd);
 544                                 if (error == 0)
 545 #endif
 546                                         shm_dotruncate(shmfd, 0);
 547                         }
 548                         if (error == 0)
 549                                 shm_hold(shmfd);
 550                 }
 551                 sx_xunlock(&shm_dict_lock);
 552
 553                 if (error) {
 554                         fdclose(fdp, fp, fd, td);
 555                         fdrop(fp, td);
 556                         return (error);
 557                 }
 558         }
 559
 560         finit(fp, FFLAGS(uap->flags & O_ACCMODE), DTYPE_SHM, shmfd, &shm_ops);
 561
 562         FILEDESC_XLOCK(fdp);
 563         if (fdp->fd_ofiles[fd] == fp)
 564                 fdp->fd_ofileflags[fd] |= UF_EXCLOSE;
 565         FILEDESC_XUNLOCK(fdp);
 566         td->td_retval[0] = fd;
 567         fdrop(fp, td);
 568
 569         return (0);
 570 }
 571
 572 int
 573 shm_unlink(struct thread *td, struct shm_unlink_args *uap)
 574 {
 575         char *path;
 576         Fnv32_t fnv;
 577         int error;
 578
 579         path = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
 580         error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
 581         if (error) {
 582                 free(path, M_TEMP);
 583                 return (error);
 584         }
 585
 586         fnv = fnv_32_str(path, FNV1_32_INIT);
 587         sx_xlock(&shm_dict_lock);
 588         error = shm_remove(path, fnv, td->td_ucred);
 589         sx_xunlock(&shm_dict_lock);
 590         free(path, M_TEMP);
 591
 592         return (error);
 593 }
 594
 595 /*
 596  * mmap() helper to validate mmap() requests against shm object state
 597  * and give mmap() the vm_object to use for the mapping.
 598  */
 599 int
 600 shm_mmap(struct shmfd *shmfd, vm_size_t objsize, vm_ooffset_t foff,
 601     vm_object_t *obj)
 602 {
 603
 604         /*
 605          * XXXRW: This validation is probably insufficient, and subject to
 606          * sign errors.  It should be fixed.
 607          */
 608         if (foff >= shmfd->shm_size || foff + objsize > shmfd->shm_size)
 609                 return (EINVAL);
 610
 611         mtx_lock(&shm_timestamp_lock);
 612         vfs_timestamp(&shmfd->shm_atime);
 613         mtx_unlock(&shm_timestamp_lock);
 614         vm_object_reference(shmfd->shm_object);
 615         *obj = shmfd->shm_object;
 616         return (0);
 617 }