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  * (4) 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 
   51 #include <sys/cdefs.h>
   52 __FBSDID("$FreeBSD: releng/9.0/sys/kern/uipc_shm.c 225617 2011-09-16 13:58:51Z kmacy $");
   53 
   54 #include "opt_capsicum.h"
   55 
   56 #include <sys/param.h>
   57 #include <sys/capability.h>
   58 #include <sys/fcntl.h>
   59 #include <sys/file.h>
   60 #include <sys/filedesc.h>
   61 #include <sys/fnv_hash.h>
   62 #include <sys/kernel.h>
   63 #include <sys/lock.h>
   64 #include <sys/malloc.h>
   65 #include <sys/mman.h>
   66 #include <sys/mutex.h>
   67 #include <sys/priv.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 static fo_chmod_t       shm_chmod;
  124 static fo_chown_t       shm_chown;
  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_chmod = shm_chmod,
  137         .fo_chown = shm_chown,
  138         .fo_flags = DFLAG_PASSABLE
  139 };
  140 
  141 FEATURE(posix_shm, "POSIX shared memory");
  142 
  143 static int
  144 shm_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
  145     int flags, struct thread *td)
  146 {
  147 
  148         return (EOPNOTSUPP);
  149 }
  150 
  151 static int
  152 shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
  153     int flags, struct thread *td)
  154 {
  155 
  156         return (EOPNOTSUPP);
  157 }
  158 
  159 static int
  160 shm_truncate(struct file *fp, off_t length, struct ucred *active_cred,
  161     struct thread *td)
  162 {
  163         struct shmfd *shmfd;
  164 #ifdef MAC
  165         int error;
  166 #endif
  167 
  168         shmfd = fp->f_data;
  169 #ifdef MAC
  170         error = mac_posixshm_check_truncate(active_cred, fp->f_cred, shmfd);
  171         if (error)
  172                 return (error);
  173 #endif
  174         return (shm_dotruncate(shmfd, length));
  175 }
  176 
  177 static int
  178 shm_ioctl(struct file *fp, u_long com, void *data,
  179     struct ucred *active_cred, struct thread *td)
  180 {
  181 
  182         return (EOPNOTSUPP);
  183 }
  184 
  185 static int
  186 shm_poll(struct file *fp, int events, struct ucred *active_cred,
  187     struct thread *td)
  188 {
  189 
  190         return (EOPNOTSUPP);
  191 }
  192 
  193 static int
  194 shm_kqfilter(struct file *fp, struct knote *kn)
  195 {
  196 
  197         return (EOPNOTSUPP);
  198 }
  199 
  200 static int
  201 shm_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
  202     struct thread *td)
  203 {
  204         struct shmfd *shmfd;
  205 #ifdef MAC
  206         int error;
  207 #endif
  208 
  209         shmfd = fp->f_data;
  210 
  211 #ifdef MAC
  212         error = mac_posixshm_check_stat(active_cred, fp->f_cred, shmfd);
  213         if (error)
  214                 return (error);
  215 #endif
  216         
  217         /*
  218          * Attempt to return sanish values for fstat() on a memory file
  219          * descriptor.
  220          */
  221         bzero(sb, sizeof(*sb));
  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         mtx_lock(&shm_timestamp_lock);
  226         sb->st_atim = shmfd->shm_atime;
  227         sb->st_ctim = shmfd->shm_ctime;
  228         sb->st_mtim = shmfd->shm_mtime;
  229         sb->st_birthtim = shmfd->shm_birthtime;
  230         sb->st_mode = S_IFREG | shmfd->shm_mode;                /* XXX */
  231         sb->st_uid = shmfd->shm_uid;
  232         sb->st_gid = shmfd->shm_gid;
  233         mtx_unlock(&shm_timestamp_lock);
  234 
  235         return (0);
  236 }
  237 
  238 static int
  239 shm_close(struct file *fp, struct thread *td)
  240 {
  241         struct shmfd *shmfd;
  242 
  243         shmfd = fp->f_data;
  244         fp->f_data = NULL;
  245         shm_drop(shmfd);
  246 
  247         return (0);
  248 }
  249 
  250 static int
  251 shm_dotruncate(struct shmfd *shmfd, off_t length)
  252 {
  253         vm_object_t object;
  254         vm_page_t m;
  255         vm_pindex_t nobjsize;
  256         vm_ooffset_t delta;
  257 
  258         object = shmfd->shm_object;
  259         VM_OBJECT_LOCK(object);
  260         if (length == shmfd->shm_size) {
  261                 VM_OBJECT_UNLOCK(object);
  262                 return (0);
  263         }
  264         nobjsize = OFF_TO_IDX(length + PAGE_MASK);
  265 
  266         /* Are we shrinking?  If so, trim the end. */
  267         if (length < shmfd->shm_size) {
  268                 delta = ptoa(object->size - nobjsize);
  269 
  270                 /* Toss in memory pages. */
  271                 if (nobjsize < object->size)
  272                         vm_object_page_remove(object, nobjsize, object->size,
  273                             0);
  274 
  275                 /* Toss pages from swap. */
  276                 if (object->type == OBJT_SWAP)
  277                         swap_pager_freespace(object, nobjsize, delta);
  278 
  279                 /* Free the swap accounted for shm */
  280                 swap_release_by_cred(delta, object->cred);
  281                 object->charge -= delta;
  282 
  283                 /*
  284                  * If the last page is partially mapped, then zero out
  285                  * the garbage at the end of the page.  See comments
  286                  * in vnode_pager_setsize() for more details.
  287                  *
  288                  * XXXJHB: This handles in memory pages, but what about
  289                  * a page swapped out to disk?
  290                  */
  291                 if ((length & PAGE_MASK) &&
  292                     (m = vm_page_lookup(object, OFF_TO_IDX(length))) != NULL &&
  293                     m->valid != 0) {
  294                         int base = (int)length & PAGE_MASK;
  295                         int size = PAGE_SIZE - base;
  296 
  297                         pmap_zero_page_area(m, base, size);
  298 
  299                         /*
  300                          * Update the valid bits to reflect the blocks that
  301                          * have been zeroed.  Some of these valid bits may
  302                          * have already been set.
  303                          */
  304                         vm_page_set_valid(m, base, size);
  305 
  306                         /*
  307                          * Round "base" to the next block boundary so that the
  308                          * dirty bit for a partially zeroed block is not
  309                          * cleared.
  310                          */
  311                         base = roundup2(base, DEV_BSIZE);
  312 
  313                         vm_page_clear_dirty(m, base, PAGE_SIZE - base);
  314                 } else if ((length & PAGE_MASK) &&
  315                     __predict_false(object->cache != NULL)) {
  316                         vm_page_cache_free(object, OFF_TO_IDX(length),
  317                             nobjsize);
  318                 }
  319         } else {
  320 
  321                 /* Attempt to reserve the swap */
  322                 delta = ptoa(nobjsize - object->size);
  323                 if (!swap_reserve_by_cred(delta, object->cred)) {
  324                         VM_OBJECT_UNLOCK(object);
  325                         return (ENOMEM);
  326                 }
  327                 object->charge += delta;
  328         }
  329         shmfd->shm_size = length;
  330         mtx_lock(&shm_timestamp_lock);
  331         vfs_timestamp(&shmfd->shm_ctime);
  332         shmfd->shm_mtime = shmfd->shm_ctime;
  333         mtx_unlock(&shm_timestamp_lock);
  334         object->size = nobjsize;
  335         VM_OBJECT_UNLOCK(object);
  336         return (0);
  337 }
  338 
  339 /*
  340  * shmfd object management including creation and reference counting
  341  * routines.
  342  */
  343 static struct shmfd *
  344 shm_alloc(struct ucred *ucred, mode_t mode)
  345 {
  346         struct shmfd *shmfd;
  347 
  348         shmfd = malloc(sizeof(*shmfd), M_SHMFD, M_WAITOK | M_ZERO);
  349         shmfd->shm_size = 0;
  350         shmfd->shm_uid = ucred->cr_uid;
  351         shmfd->shm_gid = ucred->cr_gid;
  352         shmfd->shm_mode = mode;
  353         shmfd->shm_object = vm_pager_allocate(OBJT_DEFAULT, NULL,
  354             shmfd->shm_size, VM_PROT_DEFAULT, 0, ucred);
  355         KASSERT(shmfd->shm_object != NULL, ("shm_create: vm_pager_allocate"));
  356         VM_OBJECT_LOCK(shmfd->shm_object);
  357         vm_object_clear_flag(shmfd->shm_object, OBJ_ONEMAPPING);
  358         vm_object_set_flag(shmfd->shm_object, OBJ_NOSPLIT);
  359         VM_OBJECT_UNLOCK(shmfd->shm_object);
  360         vfs_timestamp(&shmfd->shm_birthtime);
  361         shmfd->shm_atime = shmfd->shm_mtime = shmfd->shm_ctime =
  362             shmfd->shm_birthtime;
  363         refcount_init(&shmfd->shm_refs, 1);
  364 #ifdef MAC
  365         mac_posixshm_init(shmfd);
  366         mac_posixshm_create(ucred, shmfd);
  367 #endif
  368 
  369         return (shmfd);
  370 }
  371 
  372 static struct shmfd *
  373 shm_hold(struct shmfd *shmfd)
  374 {
  375 
  376         refcount_acquire(&shmfd->shm_refs);
  377         return (shmfd);
  378 }
  379 
  380 static void
  381 shm_drop(struct shmfd *shmfd)
  382 {
  383 
  384         if (refcount_release(&shmfd->shm_refs)) {
  385 #ifdef MAC
  386                 mac_posixshm_destroy(shmfd);
  387 #endif
  388                 vm_object_deallocate(shmfd->shm_object);
  389                 free(shmfd, M_SHMFD);
  390         }
  391 }
  392 
  393 /*
  394  * Determine if the credentials have sufficient permissions for a
  395  * specified combination of FREAD and FWRITE.
  396  */
  397 static int
  398 shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags)
  399 {
  400         accmode_t accmode;
  401         int error;
  402 
  403         accmode = 0;
  404         if (flags & FREAD)
  405                 accmode |= VREAD;
  406         if (flags & FWRITE)
  407                 accmode |= VWRITE;
  408         mtx_lock(&shm_timestamp_lock);
  409         error = vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid, shmfd->shm_gid,
  410             accmode, ucred, NULL);
  411         mtx_unlock(&shm_timestamp_lock);
  412         return (error);
  413 }
  414 
  415 /*
  416  * Dictionary management.  We maintain an in-kernel dictionary to map
  417  * paths to shmfd objects.  We use the FNV hash on the path to store
  418  * the mappings in a hash table.
  419  */
  420 static void
  421 shm_dict_init(void *arg)
  422 {
  423 
  424         mtx_init(&shm_timestamp_lock, "shm timestamps", NULL, MTX_DEF);
  425         sx_init(&shm_dict_lock, "shm dictionary");
  426         shm_dictionary = hashinit(1024, M_SHMFD, &shm_hash);
  427 }
  428 SYSINIT(shm_dict_init, SI_SUB_SYSV_SHM, SI_ORDER_ANY, shm_dict_init, NULL);
  429 
  430 static struct shmfd *
  431 shm_lookup(char *path, Fnv32_t fnv)
  432 {
  433         struct shm_mapping *map;
  434 
  435         LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
  436                 if (map->sm_fnv != fnv)
  437                         continue;
  438                 if (strcmp(map->sm_path, path) == 0)
  439                         return (map->sm_shmfd);
  440         }
  441 
  442         return (NULL);
  443 }
  444 
  445 static void
  446 shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd)
  447 {
  448         struct shm_mapping *map;
  449 
  450         map = malloc(sizeof(struct shm_mapping), M_SHMFD, M_WAITOK);
  451         map->sm_path = path;
  452         map->sm_fnv = fnv;
  453         map->sm_shmfd = shm_hold(shmfd);
  454         LIST_INSERT_HEAD(SHM_HASH(fnv), map, sm_link);
  455 }
  456 
  457 static int
  458 shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred)
  459 {
  460         struct shm_mapping *map;
  461         int error;
  462 
  463         LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
  464                 if (map->sm_fnv != fnv)
  465                         continue;
  466                 if (strcmp(map->sm_path, path) == 0) {
  467 #ifdef MAC
  468                         error = mac_posixshm_check_unlink(ucred, map->sm_shmfd);
  469                         if (error)
  470                                 return (error);
  471 #endif
  472                         error = shm_access(map->sm_shmfd, ucred,
  473                             FREAD | FWRITE);
  474                         if (error)
  475                                 return (error);
  476                         LIST_REMOVE(map, sm_link);
  477                         shm_drop(map->sm_shmfd);
  478                         free(map->sm_path, M_SHMFD);
  479                         free(map, M_SHMFD);
  480                         return (0);
  481                 }
  482         }
  483 
  484         return (ENOENT);
  485 }
  486 
  487 /* System calls. */
  488 int
  489 sys_shm_open(struct thread *td, struct shm_open_args *uap)
  490 {
  491         struct filedesc *fdp;
  492         struct shmfd *shmfd;
  493         struct file *fp;
  494         char *path;
  495         Fnv32_t fnv;
  496         mode_t cmode;
  497         int fd, error;
  498 
  499 #ifdef CAPABILITY_MODE
  500         /*
  501          * shm_open(2) is only allowed for anonymous objects.
  502          */
  503         if (IN_CAPABILITY_MODE(td) && (uap->path != SHM_ANON))
  504                 return (ECAPMODE);
  505 #endif
  506 
  507         if ((uap->flags & O_ACCMODE) != O_RDONLY &&
  508             (uap->flags & O_ACCMODE) != O_RDWR)
  509                 return (EINVAL);
  510 
  511         if ((uap->flags & ~(O_ACCMODE | O_CREAT | O_EXCL | O_TRUNC)) != 0)
  512                 return (EINVAL);
  513 
  514         fdp = td->td_proc->p_fd;
  515         cmode = (uap->mode & ~fdp->fd_cmask) & ACCESSPERMS;
  516 
  517         error = falloc(td, &fp, &fd, 0);
  518         if (error)
  519                 return (error);
  520 
  521         /* A SHM_ANON path pointer creates an anonymous object. */
  522         if (uap->path == SHM_ANON) {
  523                 /* A read-only anonymous object is pointless. */
  524                 if ((uap->flags & O_ACCMODE) == O_RDONLY) {
  525                         fdclose(fdp, fp, fd, td);
  526                         fdrop(fp, td);
  527                         return (EINVAL);
  528                 }
  529                 shmfd = shm_alloc(td->td_ucred, cmode);
  530         } else {
  531                 path = malloc(MAXPATHLEN, M_SHMFD, M_WAITOK);
  532                 error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
  533 
  534                 /* Require paths to start with a '/' character. */
  535                 if (error == 0 && path[0] != '/')
  536                         error = EINVAL;
  537                 if (error) {
  538                         fdclose(fdp, fp, fd, td);
  539                         fdrop(fp, td);
  540                         free(path, M_SHMFD);
  541                         return (error);
  542                 }
  543 
  544                 fnv = fnv_32_str(path, FNV1_32_INIT);
  545                 sx_xlock(&shm_dict_lock);
  546                 shmfd = shm_lookup(path, fnv);
  547                 if (shmfd == NULL) {
  548                         /* Object does not yet exist, create it if requested. */
  549                         if (uap->flags & O_CREAT) {
  550 #ifdef MAC
  551                                 error = mac_posixshm_check_create(td->td_ucred,
  552                                     path);
  553                                 if (error == 0) {
  554 #endif
  555                                         shmfd = shm_alloc(td->td_ucred, cmode);
  556                                         shm_insert(path, fnv, shmfd);
  557 #ifdef MAC
  558                                 }
  559 #endif
  560                         } else {
  561                                 free(path, M_SHMFD);
  562                                 error = ENOENT;
  563                         }
  564                 } else {
  565                         /*
  566                          * Object already exists, obtain a new
  567                          * reference if requested and permitted.
  568                          */
  569                         free(path, M_SHMFD);
  570                         if ((uap->flags & (O_CREAT | O_EXCL)) ==
  571                             (O_CREAT | O_EXCL))
  572                                 error = EEXIST;
  573                         else {
  574 #ifdef MAC
  575                                 error = mac_posixshm_check_open(td->td_ucred,
  576                                     shmfd, FFLAGS(uap->flags & O_ACCMODE));
  577                                 if (error == 0)
  578 #endif
  579                                 error = shm_access(shmfd, td->td_ucred,
  580                                     FFLAGS(uap->flags & O_ACCMODE));
  581                         }
  582 
  583                         /*
  584                          * Truncate the file back to zero length if
  585                          * O_TRUNC was specified and the object was
  586                          * opened with read/write.
  587                          */
  588                         if (error == 0 &&
  589                             (uap->flags & (O_ACCMODE | O_TRUNC)) ==
  590                             (O_RDWR | O_TRUNC)) {
  591 #ifdef MAC
  592                                 error = mac_posixshm_check_truncate(
  593                                         td->td_ucred, fp->f_cred, shmfd);
  594                                 if (error == 0)
  595 #endif
  596                                         shm_dotruncate(shmfd, 0);
  597                         }
  598                         if (error == 0)
  599                                 shm_hold(shmfd);
  600                 }
  601                 sx_xunlock(&shm_dict_lock);
  602 
  603                 if (error) {
  604                         fdclose(fdp, fp, fd, td);
  605                         fdrop(fp, td);
  606                         return (error);
  607                 }
  608         }
  609 
  610         finit(fp, FFLAGS(uap->flags & O_ACCMODE), DTYPE_SHM, shmfd, &shm_ops);
  611 
  612         FILEDESC_XLOCK(fdp);
  613         if (fdp->fd_ofiles[fd] == fp)
  614                 fdp->fd_ofileflags[fd] |= UF_EXCLOSE;
  615         FILEDESC_XUNLOCK(fdp);
  616         td->td_retval[0] = fd;
  617         fdrop(fp, td);
  618 
  619         return (0);
  620 }
  621 
  622 int
  623 sys_shm_unlink(struct thread *td, struct shm_unlink_args *uap)
  624 {
  625         char *path;
  626         Fnv32_t fnv;
  627         int error;
  628 
  629         path = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
  630         error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
  631         if (error) {
  632                 free(path, M_TEMP);
  633                 return (error);
  634         }
  635 
  636         fnv = fnv_32_str(path, FNV1_32_INIT);
  637         sx_xlock(&shm_dict_lock);
  638         error = shm_remove(path, fnv, td->td_ucred);
  639         sx_xunlock(&shm_dict_lock);
  640         free(path, M_TEMP);
  641 
  642         return (error);
  643 }
  644 
  645 /*
  646  * mmap() helper to validate mmap() requests against shm object state
  647  * and give mmap() the vm_object to use for the mapping.
  648  */
  649 int
  650 shm_mmap(struct shmfd *shmfd, vm_size_t objsize, vm_ooffset_t foff,
  651     vm_object_t *obj)
  652 {
  653 
  654         /*
  655          * XXXRW: This validation is probably insufficient, and subject to
  656          * sign errors.  It should be fixed.
  657          */
  658         if (foff >= shmfd->shm_size ||
  659             foff + objsize > round_page(shmfd->shm_size))
  660                 return (EINVAL);
  661 
  662         mtx_lock(&shm_timestamp_lock);
  663         vfs_timestamp(&shmfd->shm_atime);
  664         mtx_unlock(&shm_timestamp_lock);
  665         vm_object_reference(shmfd->shm_object);
  666         *obj = shmfd->shm_object;
  667         return (0);
  668 }
  669 
  670 static int
  671 shm_chmod(struct file *fp, mode_t mode, struct ucred *active_cred,
  672     struct thread *td)
  673 {
  674         struct shmfd *shmfd;
  675         int error;
  676 
  677         error = 0;
  678         shmfd = fp->f_data;
  679         mtx_lock(&shm_timestamp_lock);
  680         /*
  681          * SUSv4 says that x bits of permission need not be affected.
  682          * Be consistent with our shm_open there.
  683          */
  684 #ifdef MAC
  685         error = mac_posixshm_check_setmode(active_cred, shmfd, mode);
  686         if (error != 0)
  687                 goto out;
  688 #endif
  689         error = vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid,
  690             shmfd->shm_gid, VADMIN, active_cred, NULL);
  691         if (error != 0)
  692                 goto out;
  693         shmfd->shm_mode = mode & ACCESSPERMS;
  694 out:
  695         mtx_unlock(&shm_timestamp_lock);
  696         return (error);
  697 }
  698 
  699 static int
  700 shm_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
  701     struct thread *td)
  702 {
  703         struct shmfd *shmfd;
  704         int error;
  705 
  706         error = 0;
  707         shmfd = fp->f_data;
  708         mtx_lock(&shm_timestamp_lock);
  709 #ifdef MAC
  710         error = mac_posixshm_check_setowner(active_cred, shmfd, uid, gid);
  711         if (error != 0)
  712                 goto out;
  713 #endif
  714         if (uid == (uid_t)-1)
  715                 uid = shmfd->shm_uid;
  716         if (gid == (gid_t)-1)
  717                  gid = shmfd->shm_gid;
  718         if (((uid != shmfd->shm_uid && uid != active_cred->cr_uid) ||
  719             (gid != shmfd->shm_gid && !groupmember(gid, active_cred))) &&
  720             (error = priv_check_cred(active_cred, PRIV_VFS_CHOWN, 0)))
  721                 goto out;
  722         shmfd->shm_uid = uid;
  723         shmfd->shm_gid = gid;
  724 out:
  725         mtx_unlock(&shm_timestamp_lock);
  726         return (error);
  727 }

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