The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/uipc_shm.c

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    1 /*-
    2  * Copyright (c) 2006, 2011 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  * (1) 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  * (2) Add support for this file type to fstat(1).
   39  *
   40  * (3) Resource limits?  Does this need its own resource limits or are the
   41  *     existing limits in mmap(2) sufficient?
   42  */
   43 
   44 #include <sys/cdefs.h>
   45 __FBSDID("$FreeBSD: stable/10/sys/kern/uipc_shm.c 325783 2017-11-13 23:21:17Z jamie $");
   46 
   47 #include "opt_capsicum.h"
   48 #include "opt_ktrace.h"
   49 
   50 #include <sys/param.h>
   51 #include <sys/capsicum.h>
   52 #include <sys/conf.h>
   53 #include <sys/fcntl.h>
   54 #include <sys/file.h>
   55 #include <sys/filedesc.h>
   56 #include <sys/fnv_hash.h>
   57 #include <sys/kernel.h>
   58 #include <sys/uio.h>
   59 #include <sys/signal.h>
   60 #include <sys/jail.h>
   61 #include <sys/ktrace.h>
   62 #include <sys/lock.h>
   63 #include <sys/malloc.h>
   64 #include <sys/mman.h>
   65 #include <sys/mutex.h>
   66 #include <sys/priv.h>
   67 #include <sys/proc.h>
   68 #include <sys/refcount.h>
   69 #include <sys/resourcevar.h>
   70 #include <sys/rwlock.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 #include <sys/unistd.h>
   79 
   80 #include <security/mac/mac_framework.h>
   81 
   82 #include <vm/vm.h>
   83 #include <vm/vm_param.h>
   84 #include <vm/pmap.h>
   85 #include <vm/vm_extern.h>
   86 #include <vm/vm_map.h>
   87 #include <vm/vm_kern.h>
   88 #include <vm/vm_object.h>
   89 #include <vm/vm_page.h>
   90 #include <vm/vm_pageout.h>
   91 #include <vm/vm_pager.h>
   92 #include <vm/swap_pager.h>
   93 
   94 struct shm_mapping {
   95         char            *sm_path;
   96         Fnv32_t         sm_fnv;
   97         struct shmfd    *sm_shmfd;
   98         LIST_ENTRY(shm_mapping) sm_link;
   99 };
  100 
  101 static MALLOC_DEFINE(M_SHMFD, "shmfd", "shared memory file descriptor");
  102 static LIST_HEAD(, shm_mapping) *shm_dictionary;
  103 static struct sx shm_dict_lock;
  104 static struct mtx shm_timestamp_lock;
  105 static u_long shm_hash;
  106 static struct unrhdr *shm_ino_unr;
  107 static dev_t shm_dev_ino;
  108 
  109 #define SHM_HASH(fnv)   (&shm_dictionary[(fnv) & shm_hash])
  110 
  111 static int      shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags);
  112 static struct shmfd *shm_alloc(struct ucred *ucred, mode_t mode);
  113 static void     shm_init(void *arg);
  114 static void     shm_drop(struct shmfd *shmfd);
  115 static struct shmfd *shm_hold(struct shmfd *shmfd);
  116 static void     shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd);
  117 static struct shmfd *shm_lookup(char *path, Fnv32_t fnv);
  118 static int      shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred);
  119 static int      shm_dotruncate(struct shmfd *shmfd, off_t length);
  120 
  121 static fo_rdwr_t        shm_read;
  122 static fo_rdwr_t        shm_write;
  123 static fo_truncate_t    shm_truncate;
  124 static fo_ioctl_t       shm_ioctl;
  125 static fo_poll_t        shm_poll;
  126 static fo_kqfilter_t    shm_kqfilter;
  127 static fo_stat_t        shm_stat;
  128 static fo_close_t       shm_close;
  129 static fo_chmod_t       shm_chmod;
  130 static fo_chown_t       shm_chown;
  131 static fo_seek_t        shm_seek;
  132 
  133 /* File descriptor operations. */
  134 static struct fileops shm_ops = {
  135         .fo_read = shm_read,
  136         .fo_write = shm_write,
  137         .fo_truncate = shm_truncate,
  138         .fo_ioctl = shm_ioctl,
  139         .fo_poll = shm_poll,
  140         .fo_kqfilter = shm_kqfilter,
  141         .fo_stat = shm_stat,
  142         .fo_close = shm_close,
  143         .fo_chmod = shm_chmod,
  144         .fo_chown = shm_chown,
  145         .fo_sendfile = vn_sendfile,
  146         .fo_seek = shm_seek,
  147         .fo_flags = DFLAG_PASSABLE | DFLAG_SEEKABLE
  148 };
  149 
  150 FEATURE(posix_shm, "POSIX shared memory");
  151 
  152 static int
  153 uiomove_object_page(vm_object_t obj, size_t len, struct uio *uio)
  154 {
  155         vm_page_t m;
  156         vm_pindex_t idx;
  157         size_t tlen;
  158         int error, offset, rv;
  159 
  160         idx = OFF_TO_IDX(uio->uio_offset);
  161         offset = uio->uio_offset & PAGE_MASK;
  162         tlen = MIN(PAGE_SIZE - offset, len);
  163 
  164         VM_OBJECT_WLOCK(obj);
  165 
  166         /*
  167          * Parallel reads of the page content from disk are prevented
  168          * by exclusive busy.
  169          *
  170          * Although the tmpfs vnode lock is held here, it is
  171          * nonetheless safe to sleep waiting for a free page.  The
  172          * pageout daemon does not need to acquire the tmpfs vnode
  173          * lock to page out tobj's pages because tobj is a OBJT_SWAP
  174          * type object.
  175          */
  176         m = vm_page_grab(obj, idx, VM_ALLOC_NORMAL);
  177         if (m->valid != VM_PAGE_BITS_ALL) {
  178                 if (vm_pager_has_page(obj, idx, NULL, NULL)) {
  179                         rv = vm_pager_get_pages(obj, &m, 1, 0);
  180                         m = vm_page_lookup(obj, idx);
  181                         if (m == NULL) {
  182                                 printf(
  183                     "uiomove_object: vm_obj %p idx %jd null lookup rv %d\n",
  184                                     obj, idx, rv);
  185                                 VM_OBJECT_WUNLOCK(obj);
  186                                 return (EIO);
  187                         }
  188                         if (rv != VM_PAGER_OK) {
  189                                 printf(
  190             "uiomove_object: vm_obj %p idx %jd valid %x pager error %d\n",
  191                                     obj, idx, m->valid, rv);
  192                                 vm_page_lock(m);
  193                                 vm_page_free(m);
  194                                 vm_page_unlock(m);
  195                                 VM_OBJECT_WUNLOCK(obj);
  196                                 return (EIO);
  197                         }
  198                 } else
  199                         vm_page_zero_invalid(m, TRUE);
  200         }
  201         vm_page_xunbusy(m);
  202         vm_page_lock(m);
  203         vm_page_hold(m);
  204         if (m->queue == PQ_NONE) {
  205                 vm_page_deactivate(m);
  206         } else {
  207                 /* Requeue to maintain LRU ordering. */
  208                 vm_page_requeue(m);
  209         }
  210         vm_page_unlock(m);
  211         VM_OBJECT_WUNLOCK(obj);
  212         error = uiomove_fromphys(&m, offset, tlen, uio);
  213         if (uio->uio_rw == UIO_WRITE && error == 0) {
  214                 VM_OBJECT_WLOCK(obj);
  215                 vm_page_dirty(m);
  216                 vm_pager_page_unswapped(m);
  217                 VM_OBJECT_WUNLOCK(obj);
  218         }
  219         vm_page_lock(m);
  220         vm_page_unhold(m);
  221         vm_page_unlock(m);
  222 
  223         return (error);
  224 }
  225 
  226 int
  227 uiomove_object(vm_object_t obj, off_t obj_size, struct uio *uio)
  228 {
  229         ssize_t resid;
  230         size_t len;
  231         int error;
  232 
  233         error = 0;
  234         while ((resid = uio->uio_resid) > 0) {
  235                 if (obj_size <= uio->uio_offset)
  236                         break;
  237                 len = MIN(obj_size - uio->uio_offset, resid);
  238                 if (len == 0)
  239                         break;
  240                 error = uiomove_object_page(obj, len, uio);
  241                 if (error != 0 || resid == uio->uio_resid)
  242                         break;
  243         }
  244         return (error);
  245 }
  246 
  247 static int
  248 shm_seek(struct file *fp, off_t offset, int whence, struct thread *td)
  249 {
  250         struct shmfd *shmfd;
  251         off_t foffset;
  252         int error;
  253 
  254         shmfd = fp->f_data;
  255         foffset = foffset_lock(fp, 0);
  256         error = 0;
  257         switch (whence) {
  258         case L_INCR:
  259                 if (foffset < 0 ||
  260                     (offset > 0 && foffset > OFF_MAX - offset)) {
  261                         error = EOVERFLOW;
  262                         break;
  263                 }
  264                 offset += foffset;
  265                 break;
  266         case L_XTND:
  267                 if (offset > 0 && shmfd->shm_size > OFF_MAX - offset) {
  268                         error = EOVERFLOW;
  269                         break;
  270                 }
  271                 offset += shmfd->shm_size;
  272                 break;
  273         case L_SET:
  274                 break;
  275         default:
  276                 error = EINVAL;
  277         }
  278         if (error == 0) {
  279                 if (offset < 0 || offset > shmfd->shm_size)
  280                         error = EINVAL;
  281                 else
  282                         *(off_t *)(td->td_retval) = offset;
  283         }
  284         foffset_unlock(fp, offset, error != 0 ? FOF_NOUPDATE : 0);
  285         return (error);
  286 }
  287 
  288 static int
  289 shm_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
  290     int flags, struct thread *td)
  291 {
  292         struct shmfd *shmfd;
  293         void *rl_cookie;
  294         int error;
  295 
  296         shmfd = fp->f_data;
  297 #ifdef MAC
  298         error = mac_posixshm_check_read(active_cred, fp->f_cred, shmfd);
  299         if (error)
  300                 return (error);
  301 #endif
  302         foffset_lock_uio(fp, uio, flags);
  303         rl_cookie = rangelock_rlock(&shmfd->shm_rl, uio->uio_offset,
  304             uio->uio_offset + uio->uio_resid, &shmfd->shm_mtx);
  305         error = uiomove_object(shmfd->shm_object, shmfd->shm_size, uio);
  306         rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
  307         foffset_unlock_uio(fp, uio, flags);
  308         return (error);
  309 }
  310 
  311 static int
  312 shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
  313     int flags, struct thread *td)
  314 {
  315         struct shmfd *shmfd;
  316         void *rl_cookie;
  317         int error;
  318 
  319         shmfd = fp->f_data;
  320 #ifdef MAC
  321         error = mac_posixshm_check_write(active_cred, fp->f_cred, shmfd);
  322         if (error)
  323                 return (error);
  324 #endif
  325         foffset_lock_uio(fp, uio, flags);
  326         if ((flags & FOF_OFFSET) == 0) {
  327                 rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
  328                     &shmfd->shm_mtx);
  329         } else {
  330                 rl_cookie = rangelock_wlock(&shmfd->shm_rl, uio->uio_offset,
  331                     uio->uio_offset + uio->uio_resid, &shmfd->shm_mtx);
  332         }
  333 
  334         error = uiomove_object(shmfd->shm_object, shmfd->shm_size, uio);
  335         rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
  336         foffset_unlock_uio(fp, uio, flags);
  337         return (error);
  338 }
  339 
  340 static int
  341 shm_truncate(struct file *fp, off_t length, struct ucred *active_cred,
  342     struct thread *td)
  343 {
  344         struct shmfd *shmfd;
  345 #ifdef MAC
  346         int error;
  347 #endif
  348 
  349         shmfd = fp->f_data;
  350 #ifdef MAC
  351         error = mac_posixshm_check_truncate(active_cred, fp->f_cred, shmfd);
  352         if (error)
  353                 return (error);
  354 #endif
  355         return (shm_dotruncate(shmfd, length));
  356 }
  357 
  358 static int
  359 shm_ioctl(struct file *fp, u_long com, void *data,
  360     struct ucred *active_cred, struct thread *td)
  361 {
  362 
  363         return (EOPNOTSUPP);
  364 }
  365 
  366 static int
  367 shm_poll(struct file *fp, int events, struct ucred *active_cred,
  368     struct thread *td)
  369 {
  370 
  371         return (EOPNOTSUPP);
  372 }
  373 
  374 static int
  375 shm_kqfilter(struct file *fp, struct knote *kn)
  376 {
  377 
  378         return (EOPNOTSUPP);
  379 }
  380 
  381 static int
  382 shm_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
  383     struct thread *td)
  384 {
  385         struct shmfd *shmfd;
  386 #ifdef MAC
  387         int error;
  388 #endif
  389 
  390         shmfd = fp->f_data;
  391 
  392 #ifdef MAC
  393         error = mac_posixshm_check_stat(active_cred, fp->f_cred, shmfd);
  394         if (error)
  395                 return (error);
  396 #endif
  397         
  398         /*
  399          * Attempt to return sanish values for fstat() on a memory file
  400          * descriptor.
  401          */
  402         bzero(sb, sizeof(*sb));
  403         sb->st_blksize = PAGE_SIZE;
  404         sb->st_size = shmfd->shm_size;
  405         sb->st_blocks = (sb->st_size + sb->st_blksize - 1) / sb->st_blksize;
  406         mtx_lock(&shm_timestamp_lock);
  407         sb->st_atim = shmfd->shm_atime;
  408         sb->st_ctim = shmfd->shm_ctime;
  409         sb->st_mtim = shmfd->shm_mtime;
  410         sb->st_birthtim = shmfd->shm_birthtime;
  411         sb->st_mode = S_IFREG | shmfd->shm_mode;                /* XXX */
  412         sb->st_uid = shmfd->shm_uid;
  413         sb->st_gid = shmfd->shm_gid;
  414         mtx_unlock(&shm_timestamp_lock);
  415         sb->st_dev = shm_dev_ino;
  416         sb->st_ino = shmfd->shm_ino;
  417 
  418         return (0);
  419 }
  420 
  421 static int
  422 shm_close(struct file *fp, struct thread *td)
  423 {
  424         struct shmfd *shmfd;
  425 
  426         shmfd = fp->f_data;
  427         fp->f_data = NULL;
  428         shm_drop(shmfd);
  429 
  430         return (0);
  431 }
  432 
  433 static int
  434 shm_dotruncate(struct shmfd *shmfd, off_t length)
  435 {
  436         vm_object_t object;
  437         vm_page_t m, ma[1];
  438         vm_pindex_t idx, nobjsize;
  439         vm_ooffset_t delta;
  440         int base, rv;
  441 
  442         KASSERT(length >= 0, ("shm_dotruncate: length < 0"));
  443         object = shmfd->shm_object;
  444         VM_OBJECT_WLOCK(object);
  445         if (length == shmfd->shm_size) {
  446                 VM_OBJECT_WUNLOCK(object);
  447                 return (0);
  448         }
  449         nobjsize = OFF_TO_IDX(length + PAGE_MASK);
  450 
  451         /* Are we shrinking?  If so, trim the end. */
  452         if (length < shmfd->shm_size) {
  453                 /*
  454                  * Disallow any requests to shrink the size if this
  455                  * object is mapped into the kernel.
  456                  */
  457                 if (shmfd->shm_kmappings > 0) {
  458                         VM_OBJECT_WUNLOCK(object);
  459                         return (EBUSY);
  460                 }
  461 
  462                 /*
  463                  * Zero the truncated part of the last page.
  464                  */
  465                 base = length & PAGE_MASK;
  466                 if (base != 0) {
  467                         idx = OFF_TO_IDX(length);
  468 retry:
  469                         m = vm_page_lookup(object, idx);
  470                         if (m != NULL) {
  471                                 if (vm_page_sleep_if_busy(m, "shmtrc"))
  472                                         goto retry;
  473                         } else if (vm_pager_has_page(object, idx, NULL, NULL)) {
  474                                 m = vm_page_alloc(object, idx, VM_ALLOC_NORMAL);
  475                                 if (m == NULL) {
  476                                         VM_OBJECT_WUNLOCK(object);
  477                                         VM_WAIT;
  478                                         VM_OBJECT_WLOCK(object);
  479                                         goto retry;
  480                                 } else if (m->valid != VM_PAGE_BITS_ALL) {
  481                                         ma[0] = m;
  482                                         rv = vm_pager_get_pages(object, ma, 1,
  483                                             0);
  484                                         m = vm_page_lookup(object, idx);
  485                                 } else
  486                                         /* A cached page was reactivated. */
  487                                         rv = VM_PAGER_OK;
  488                                 vm_page_lock(m);
  489                                 if (rv == VM_PAGER_OK) {
  490                                         vm_page_deactivate(m);
  491                                         vm_page_unlock(m);
  492                                         vm_page_xunbusy(m);
  493                                 } else {
  494                                         vm_page_free(m);
  495                                         vm_page_unlock(m);
  496                                         VM_OBJECT_WUNLOCK(object);
  497                                         return (EIO);
  498                                 }
  499                         }
  500                         if (m != NULL) {
  501                                 pmap_zero_page_area(m, base, PAGE_SIZE - base);
  502                                 KASSERT(m->valid == VM_PAGE_BITS_ALL,
  503                                     ("shm_dotruncate: page %p is invalid", m));
  504                                 vm_page_dirty(m);
  505                                 vm_pager_page_unswapped(m);
  506                         }
  507                 }
  508                 delta = IDX_TO_OFF(object->size - nobjsize);
  509 
  510                 /* Toss in memory pages. */
  511                 if (nobjsize < object->size)
  512                         vm_object_page_remove(object, nobjsize, object->size,
  513                             0);
  514 
  515                 /* Toss pages from swap. */
  516                 if (object->type == OBJT_SWAP)
  517                         swap_pager_freespace(object, nobjsize, delta);
  518 
  519                 /* Free the swap accounted for shm */
  520                 swap_release_by_cred(delta, object->cred);
  521                 object->charge -= delta;
  522         } else {
  523                 /* Try to reserve additional swap space. */
  524                 delta = IDX_TO_OFF(nobjsize - object->size);
  525                 if (!swap_reserve_by_cred(delta, object->cred)) {
  526                         VM_OBJECT_WUNLOCK(object);
  527                         return (ENOMEM);
  528                 }
  529                 object->charge += delta;
  530         }
  531         shmfd->shm_size = length;
  532         mtx_lock(&shm_timestamp_lock);
  533         vfs_timestamp(&shmfd->shm_ctime);
  534         shmfd->shm_mtime = shmfd->shm_ctime;
  535         mtx_unlock(&shm_timestamp_lock);
  536         object->size = nobjsize;
  537         VM_OBJECT_WUNLOCK(object);
  538         return (0);
  539 }
  540 
  541 /*
  542  * shmfd object management including creation and reference counting
  543  * routines.
  544  */
  545 static struct shmfd *
  546 shm_alloc(struct ucred *ucred, mode_t mode)
  547 {
  548         struct shmfd *shmfd;
  549         int ino;
  550 
  551         shmfd = malloc(sizeof(*shmfd), M_SHMFD, M_WAITOK | M_ZERO);
  552         shmfd->shm_size = 0;
  553         shmfd->shm_uid = ucred->cr_uid;
  554         shmfd->shm_gid = ucred->cr_gid;
  555         shmfd->shm_mode = mode;
  556         shmfd->shm_object = vm_pager_allocate(OBJT_DEFAULT, NULL,
  557             shmfd->shm_size, VM_PROT_DEFAULT, 0, ucred);
  558         KASSERT(shmfd->shm_object != NULL, ("shm_create: vm_pager_allocate"));
  559         shmfd->shm_object->pg_color = 0;
  560         VM_OBJECT_WLOCK(shmfd->shm_object);
  561         vm_object_clear_flag(shmfd->shm_object, OBJ_ONEMAPPING);
  562         vm_object_set_flag(shmfd->shm_object, OBJ_COLORED | OBJ_NOSPLIT);
  563         VM_OBJECT_WUNLOCK(shmfd->shm_object);
  564         vfs_timestamp(&shmfd->shm_birthtime);
  565         shmfd->shm_atime = shmfd->shm_mtime = shmfd->shm_ctime =
  566             shmfd->shm_birthtime;
  567         ino = alloc_unr(shm_ino_unr);
  568         if (ino == -1)
  569                 shmfd->shm_ino = 0;
  570         else
  571                 shmfd->shm_ino = ino;
  572         refcount_init(&shmfd->shm_refs, 1);
  573         mtx_init(&shmfd->shm_mtx, "shmrl", NULL, MTX_DEF);
  574         rangelock_init(&shmfd->shm_rl);
  575 #ifdef MAC
  576         mac_posixshm_init(shmfd);
  577         mac_posixshm_create(ucred, shmfd);
  578 #endif
  579 
  580         return (shmfd);
  581 }
  582 
  583 static struct shmfd *
  584 shm_hold(struct shmfd *shmfd)
  585 {
  586 
  587         refcount_acquire(&shmfd->shm_refs);
  588         return (shmfd);
  589 }
  590 
  591 static void
  592 shm_drop(struct shmfd *shmfd)
  593 {
  594 
  595         if (refcount_release(&shmfd->shm_refs)) {
  596 #ifdef MAC
  597                 mac_posixshm_destroy(shmfd);
  598 #endif
  599                 rangelock_destroy(&shmfd->shm_rl);
  600                 mtx_destroy(&shmfd->shm_mtx);
  601                 vm_object_deallocate(shmfd->shm_object);
  602                 if (shmfd->shm_ino != 0)
  603                         free_unr(shm_ino_unr, shmfd->shm_ino);
  604                 free(shmfd, M_SHMFD);
  605         }
  606 }
  607 
  608 /*
  609  * Determine if the credentials have sufficient permissions for a
  610  * specified combination of FREAD and FWRITE.
  611  */
  612 static int
  613 shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags)
  614 {
  615         accmode_t accmode;
  616         int error;
  617 
  618         accmode = 0;
  619         if (flags & FREAD)
  620                 accmode |= VREAD;
  621         if (flags & FWRITE)
  622                 accmode |= VWRITE;
  623         mtx_lock(&shm_timestamp_lock);
  624         error = vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid, shmfd->shm_gid,
  625             accmode, ucred, NULL);
  626         mtx_unlock(&shm_timestamp_lock);
  627         return (error);
  628 }
  629 
  630 /*
  631  * Dictionary management.  We maintain an in-kernel dictionary to map
  632  * paths to shmfd objects.  We use the FNV hash on the path to store
  633  * the mappings in a hash table.
  634  */
  635 static void
  636 shm_init(void *arg)
  637 {
  638 
  639         mtx_init(&shm_timestamp_lock, "shm timestamps", NULL, MTX_DEF);
  640         sx_init(&shm_dict_lock, "shm dictionary");
  641         shm_dictionary = hashinit(1024, M_SHMFD, &shm_hash);
  642         shm_ino_unr = new_unrhdr(1, INT32_MAX, NULL);
  643         KASSERT(shm_ino_unr != NULL, ("shm fake inodes not initialized"));
  644         shm_dev_ino = devfs_alloc_cdp_inode();
  645         KASSERT(shm_dev_ino > 0, ("shm dev inode not initialized"));
  646 }
  647 SYSINIT(shm_init, SI_SUB_SYSV_SHM, SI_ORDER_ANY, shm_init, NULL);
  648 
  649 static struct shmfd *
  650 shm_lookup(char *path, Fnv32_t fnv)
  651 {
  652         struct shm_mapping *map;
  653 
  654         LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
  655                 if (map->sm_fnv != fnv)
  656                         continue;
  657                 if (strcmp(map->sm_path, path) == 0)
  658                         return (map->sm_shmfd);
  659         }
  660 
  661         return (NULL);
  662 }
  663 
  664 static void
  665 shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd)
  666 {
  667         struct shm_mapping *map;
  668 
  669         map = malloc(sizeof(struct shm_mapping), M_SHMFD, M_WAITOK);
  670         map->sm_path = path;
  671         map->sm_fnv = fnv;
  672         map->sm_shmfd = shm_hold(shmfd);
  673         shmfd->shm_path = path;
  674         LIST_INSERT_HEAD(SHM_HASH(fnv), map, sm_link);
  675 }
  676 
  677 static int
  678 shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred)
  679 {
  680         struct shm_mapping *map;
  681         int error;
  682 
  683         LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
  684                 if (map->sm_fnv != fnv)
  685                         continue;
  686                 if (strcmp(map->sm_path, path) == 0) {
  687 #ifdef MAC
  688                         error = mac_posixshm_check_unlink(ucred, map->sm_shmfd);
  689                         if (error)
  690                                 return (error);
  691 #endif
  692                         error = shm_access(map->sm_shmfd, ucred,
  693                             FREAD | FWRITE);
  694                         if (error)
  695                                 return (error);
  696                         map->sm_shmfd->shm_path = NULL;
  697                         LIST_REMOVE(map, sm_link);
  698                         shm_drop(map->sm_shmfd);
  699                         free(map->sm_path, M_SHMFD);
  700                         free(map, M_SHMFD);
  701                         return (0);
  702                 }
  703         }
  704 
  705         return (ENOENT);
  706 }
  707 
  708 /* System calls. */
  709 int
  710 sys_shm_open(struct thread *td, struct shm_open_args *uap)
  711 {
  712         struct filedesc *fdp;
  713         struct shmfd *shmfd;
  714         struct file *fp;
  715         char *path;
  716         const char *pr_path;
  717         size_t pr_pathlen;
  718         Fnv32_t fnv;
  719         mode_t cmode;
  720         int fd, error;
  721 
  722 #ifdef CAPABILITY_MODE
  723         /*
  724          * shm_open(2) is only allowed for anonymous objects.
  725          */
  726         if (IN_CAPABILITY_MODE(td) && (uap->path != SHM_ANON))
  727                 return (ECAPMODE);
  728 #endif
  729 
  730         if ((uap->flags & O_ACCMODE) != O_RDONLY &&
  731             (uap->flags & O_ACCMODE) != O_RDWR)
  732                 return (EINVAL);
  733 
  734         if ((uap->flags & ~(O_ACCMODE | O_CREAT | O_EXCL | O_TRUNC | O_CLOEXEC)) != 0)
  735                 return (EINVAL);
  736 
  737         fdp = td->td_proc->p_fd;
  738         cmode = (uap->mode & ~fdp->fd_cmask) & ACCESSPERMS;
  739 
  740         error = falloc(td, &fp, &fd, O_CLOEXEC);
  741         if (error)
  742                 return (error);
  743 
  744         /* A SHM_ANON path pointer creates an anonymous object. */
  745         if (uap->path == SHM_ANON) {
  746                 /* A read-only anonymous object is pointless. */
  747                 if ((uap->flags & O_ACCMODE) == O_RDONLY) {
  748                         fdclose(td, fp, fd);
  749                         fdrop(fp, td);
  750                         return (EINVAL);
  751                 }
  752                 shmfd = shm_alloc(td->td_ucred, cmode);
  753         } else {
  754                 path = malloc(MAXPATHLEN, M_SHMFD, M_WAITOK);
  755                 pr_path = td->td_ucred->cr_prison->pr_path;
  756 
  757                 /* Construct a full pathname for jailed callers. */
  758                 pr_pathlen = strcmp(pr_path, "/") == 0 ? 0
  759                     : strlcpy(path, pr_path, MAXPATHLEN);
  760                 error = copyinstr(uap->path, path + pr_pathlen,
  761                     MAXPATHLEN - pr_pathlen, NULL);
  762 #ifdef KTRACE
  763                 if (error == 0 && KTRPOINT(curthread, KTR_NAMEI))
  764                         ktrnamei(path);
  765 #endif
  766                 /* Require paths to start with a '/' character. */
  767                 if (error == 0 && path[pr_pathlen] != '/')
  768                         error = EINVAL;
  769                 if (error) {
  770                         fdclose(td, fp, fd);
  771                         fdrop(fp, td);
  772                         free(path, M_SHMFD);
  773                         return (error);
  774                 }
  775 
  776                 fnv = fnv_32_str(path, FNV1_32_INIT);
  777                 sx_xlock(&shm_dict_lock);
  778                 shmfd = shm_lookup(path, fnv);
  779                 if (shmfd == NULL) {
  780                         /* Object does not yet exist, create it if requested. */
  781                         if (uap->flags & O_CREAT) {
  782 #ifdef MAC
  783                                 error = mac_posixshm_check_create(td->td_ucred,
  784                                     path);
  785                                 if (error == 0) {
  786 #endif
  787                                         shmfd = shm_alloc(td->td_ucred, cmode);
  788                                         shm_insert(path, fnv, shmfd);
  789 #ifdef MAC
  790                                 }
  791 #endif
  792                         } else {
  793                                 free(path, M_SHMFD);
  794                                 error = ENOENT;
  795                         }
  796                 } else {
  797                         /*
  798                          * Object already exists, obtain a new
  799                          * reference if requested and permitted.
  800                          */
  801                         free(path, M_SHMFD);
  802                         if ((uap->flags & (O_CREAT | O_EXCL)) ==
  803                             (O_CREAT | O_EXCL))
  804                                 error = EEXIST;
  805                         else {
  806 #ifdef MAC
  807                                 error = mac_posixshm_check_open(td->td_ucred,
  808                                     shmfd, FFLAGS(uap->flags & O_ACCMODE));
  809                                 if (error == 0)
  810 #endif
  811                                 error = shm_access(shmfd, td->td_ucred,
  812                                     FFLAGS(uap->flags & O_ACCMODE));
  813                         }
  814 
  815                         /*
  816                          * Truncate the file back to zero length if
  817                          * O_TRUNC was specified and the object was
  818                          * opened with read/write.
  819                          */
  820                         if (error == 0 &&
  821                             (uap->flags & (O_ACCMODE | O_TRUNC)) ==
  822                             (O_RDWR | O_TRUNC)) {
  823 #ifdef MAC
  824                                 error = mac_posixshm_check_truncate(
  825                                         td->td_ucred, fp->f_cred, shmfd);
  826                                 if (error == 0)
  827 #endif
  828                                         shm_dotruncate(shmfd, 0);
  829                         }
  830                         if (error == 0)
  831                                 shm_hold(shmfd);
  832                 }
  833                 sx_xunlock(&shm_dict_lock);
  834 
  835                 if (error) {
  836                         fdclose(td, fp, fd);
  837                         fdrop(fp, td);
  838                         return (error);
  839                 }
  840         }
  841 
  842         finit(fp, FFLAGS(uap->flags & O_ACCMODE), DTYPE_SHM, shmfd, &shm_ops);
  843 
  844         td->td_retval[0] = fd;
  845         fdrop(fp, td);
  846 
  847         return (0);
  848 }
  849 
  850 int
  851 sys_shm_unlink(struct thread *td, struct shm_unlink_args *uap)
  852 {
  853         char *path;
  854         const char *pr_path;
  855         size_t pr_pathlen;
  856         Fnv32_t fnv;
  857         int error;
  858 
  859         path = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
  860         pr_path = td->td_ucred->cr_prison->pr_path;
  861         pr_pathlen = strcmp(pr_path, "/") == 0 ? 0
  862             : strlcpy(path, pr_path, MAXPATHLEN);
  863         error = copyinstr(uap->path, path + pr_pathlen, MAXPATHLEN - pr_pathlen,
  864             NULL);
  865         if (error) {
  866                 free(path, M_TEMP);
  867                 return (error);
  868         }
  869 #ifdef KTRACE
  870         if (KTRPOINT(curthread, KTR_NAMEI))
  871                 ktrnamei(path);
  872 #endif
  873         fnv = fnv_32_str(path, FNV1_32_INIT);
  874         sx_xlock(&shm_dict_lock);
  875         error = shm_remove(path, fnv, td->td_ucred);
  876         sx_xunlock(&shm_dict_lock);
  877         free(path, M_TEMP);
  878 
  879         return (error);
  880 }
  881 
  882 /*
  883  * mmap() helper to validate mmap() requests against shm object state
  884  * and give mmap() the vm_object to use for the mapping.
  885  */
  886 int
  887 shm_mmap(struct shmfd *shmfd, vm_size_t objsize, vm_ooffset_t foff,
  888     vm_object_t *obj)
  889 {
  890 
  891         /*
  892          * XXXRW: This validation is probably insufficient, and subject to
  893          * sign errors.  It should be fixed.
  894          */
  895         if (foff >= shmfd->shm_size ||
  896             foff + objsize > round_page(shmfd->shm_size))
  897                 return (EINVAL);
  898 
  899         mtx_lock(&shm_timestamp_lock);
  900         vfs_timestamp(&shmfd->shm_atime);
  901         mtx_unlock(&shm_timestamp_lock);
  902         vm_object_reference(shmfd->shm_object);
  903         *obj = shmfd->shm_object;
  904         return (0);
  905 }
  906 
  907 static int
  908 shm_chmod(struct file *fp, mode_t mode, struct ucred *active_cred,
  909     struct thread *td)
  910 {
  911         struct shmfd *shmfd;
  912         int error;
  913 
  914         error = 0;
  915         shmfd = fp->f_data;
  916         mtx_lock(&shm_timestamp_lock);
  917         /*
  918          * SUSv4 says that x bits of permission need not be affected.
  919          * Be consistent with our shm_open there.
  920          */
  921 #ifdef MAC
  922         error = mac_posixshm_check_setmode(active_cred, shmfd, mode);
  923         if (error != 0)
  924                 goto out;
  925 #endif
  926         error = vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid,
  927             shmfd->shm_gid, VADMIN, active_cred, NULL);
  928         if (error != 0)
  929                 goto out;
  930         shmfd->shm_mode = mode & ACCESSPERMS;
  931 out:
  932         mtx_unlock(&shm_timestamp_lock);
  933         return (error);
  934 }
  935 
  936 static int
  937 shm_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
  938     struct thread *td)
  939 {
  940         struct shmfd *shmfd;
  941         int error;
  942 
  943         error = 0;
  944         shmfd = fp->f_data;
  945         mtx_lock(&shm_timestamp_lock);
  946 #ifdef MAC
  947         error = mac_posixshm_check_setowner(active_cred, shmfd, uid, gid);
  948         if (error != 0)
  949                 goto out;
  950 #endif
  951         if (uid == (uid_t)-1)
  952                 uid = shmfd->shm_uid;
  953         if (gid == (gid_t)-1)
  954                  gid = shmfd->shm_gid;
  955         if (((uid != shmfd->shm_uid && uid != active_cred->cr_uid) ||
  956             (gid != shmfd->shm_gid && !groupmember(gid, active_cred))) &&
  957             (error = priv_check_cred(active_cred, PRIV_VFS_CHOWN, 0)))
  958                 goto out;
  959         shmfd->shm_uid = uid;
  960         shmfd->shm_gid = gid;
  961 out:
  962         mtx_unlock(&shm_timestamp_lock);
  963         return (error);
  964 }
  965 
  966 /*
  967  * Helper routines to allow the backing object of a shared memory file
  968  * descriptor to be mapped in the kernel.
  969  */
  970 int
  971 shm_map(struct file *fp, size_t size, off_t offset, void **memp)
  972 {
  973         struct shmfd *shmfd;
  974         vm_offset_t kva, ofs;
  975         vm_object_t obj;
  976         int rv;
  977 
  978         if (fp->f_type != DTYPE_SHM)
  979                 return (EINVAL);
  980         shmfd = fp->f_data;
  981         obj = shmfd->shm_object;
  982         VM_OBJECT_WLOCK(obj);
  983         /*
  984          * XXXRW: This validation is probably insufficient, and subject to
  985          * sign errors.  It should be fixed.
  986          */
  987         if (offset >= shmfd->shm_size ||
  988             offset + size > round_page(shmfd->shm_size)) {
  989                 VM_OBJECT_WUNLOCK(obj);
  990                 return (EINVAL);
  991         }
  992 
  993         shmfd->shm_kmappings++;
  994         vm_object_reference_locked(obj);
  995         VM_OBJECT_WUNLOCK(obj);
  996 
  997         /* Map the object into the kernel_map and wire it. */
  998         kva = vm_map_min(kernel_map);
  999         ofs = offset & PAGE_MASK;
 1000         offset = trunc_page(offset);
 1001         size = round_page(size + ofs);
 1002         rv = vm_map_find(kernel_map, obj, offset, &kva, size, 0,
 1003             VMFS_OPTIMAL_SPACE, VM_PROT_READ | VM_PROT_WRITE,
 1004             VM_PROT_READ | VM_PROT_WRITE, 0);
 1005         if (rv == KERN_SUCCESS) {
 1006                 rv = vm_map_wire(kernel_map, kva, kva + size,
 1007                     VM_MAP_WIRE_SYSTEM | VM_MAP_WIRE_NOHOLES);
 1008                 if (rv == KERN_SUCCESS) {
 1009                         *memp = (void *)(kva + ofs);
 1010                         return (0);
 1011                 }
 1012                 vm_map_remove(kernel_map, kva, kva + size);
 1013         } else
 1014                 vm_object_deallocate(obj);
 1015 
 1016         /* On failure, drop our mapping reference. */
 1017         VM_OBJECT_WLOCK(obj);
 1018         shmfd->shm_kmappings--;
 1019         VM_OBJECT_WUNLOCK(obj);
 1020 
 1021         return (vm_mmap_to_errno(rv));
 1022 }
 1023 
 1024 /*
 1025  * We require the caller to unmap the entire entry.  This allows us to
 1026  * safely decrement shm_kmappings when a mapping is removed.
 1027  */
 1028 int
 1029 shm_unmap(struct file *fp, void *mem, size_t size)
 1030 {
 1031         struct shmfd *shmfd;
 1032         vm_map_entry_t entry;
 1033         vm_offset_t kva, ofs;
 1034         vm_object_t obj;
 1035         vm_pindex_t pindex;
 1036         vm_prot_t prot;
 1037         boolean_t wired;
 1038         vm_map_t map;
 1039         int rv;
 1040 
 1041         if (fp->f_type != DTYPE_SHM)
 1042                 return (EINVAL);
 1043         shmfd = fp->f_data;
 1044         kva = (vm_offset_t)mem;
 1045         ofs = kva & PAGE_MASK;
 1046         kva = trunc_page(kva);
 1047         size = round_page(size + ofs);
 1048         map = kernel_map;
 1049         rv = vm_map_lookup(&map, kva, VM_PROT_READ | VM_PROT_WRITE, &entry,
 1050             &obj, &pindex, &prot, &wired);
 1051         if (rv != KERN_SUCCESS)
 1052                 return (EINVAL);
 1053         if (entry->start != kva || entry->end != kva + size) {
 1054                 vm_map_lookup_done(map, entry);
 1055                 return (EINVAL);
 1056         }
 1057         vm_map_lookup_done(map, entry);
 1058         if (obj != shmfd->shm_object)
 1059                 return (EINVAL);
 1060         vm_map_remove(map, kva, kva + size);
 1061         VM_OBJECT_WLOCK(obj);
 1062         KASSERT(shmfd->shm_kmappings > 0, ("shm_unmap: object not mapped"));
 1063         shmfd->shm_kmappings--;
 1064         VM_OBJECT_WUNLOCK(obj);
 1065         return (0);
 1066 }
 1067 
 1068 void
 1069 shm_path(struct shmfd *shmfd, char *path, size_t size)
 1070 {
 1071         const char *shm_path, *pr_path;
 1072         size_t pr_pathlen;
 1073 
 1074         if (shmfd->shm_path == NULL)
 1075                 return;
 1076         sx_slock(&shm_dict_lock);
 1077         shm_path = shmfd->shm_path;
 1078         if (shm_path != NULL) {
 1079                 pr_path = curthread->td_ucred->cr_prison->pr_path;
 1080                 if (strcmp(pr_path, "/") != 0) {
 1081                         /* Return the jail-rooted pathname. */
 1082                         pr_pathlen = strlen(pr_path);
 1083                         if (strncmp(shm_path, pr_path, pr_pathlen) == 0 &&
 1084                             shm_path[pr_pathlen] == '/')
 1085                                 shm_path += pr_pathlen;
 1086                 }
 1087                 strlcpy(path, shm_path, size);
 1088         }
 1089         sx_sunlock(&shm_dict_lock);
 1090 }

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