uipc_shm.c

/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2006, 2011, 2016-2017 Robert N. M. Watson
 * All rights reserved.
 *
 * Portions of this software were developed by BAE Systems, the University of
 * Cambridge Computer Laboratory, and Memorial University under DARPA/AFRL
 * contract FA8650-15-C-7558 ("CADETS"), as part of the DARPA Transparent
 * Computing (TC) research program.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Support for shared swap-backed anonymous memory objects via
 * shm_open(2), shm_rename(2), and shm_unlink(2).
 * While most of the implementation is here, vm_mmap.c contains
 * mapping logic changes.
 *
 * posixshmcontrol(1) allows users to inspect the state of the memory
 * objects.  Per-uid swap resource limit controls total amount of
 * memory that user can consume for anonymous objects, including
 * shared.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_capsicum.h"
#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/capsicum.h>
#include <sys/conf.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/filio.h>
#include <sys/fnv_hash.h>
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/uio.h>
#include <sys/signal.h>
#include <sys/jail.h>
#include <sys/ktrace.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mman.h>
#include <sys/mutex.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/refcount.h>
#include <sys/resourcevar.h>
#include <sys/rwlock.h>
#include <sys/sbuf.h>
#include <sys/stat.h>
#include <sys/syscallsubr.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/systm.h>
#include <sys/sx.h>
#include <sys/time.h>
#include <sys/vnode.h>
#include <sys/unistd.h>
#include <sys/user.h>

#include <security/audit/audit.h>
#include <security/mac/mac_framework.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#include <vm/vm_extern.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pager.h>
#include <vm/swap_pager.h>

struct shm_mapping {
	char		*sm_path;
	Fnv32_t		sm_fnv;
	struct shmfd	*sm_shmfd;
	LIST_ENTRY(shm_mapping) sm_link;
};

static MALLOC_DEFINE(M_SHMFD, "shmfd", "shared memory file descriptor");
static LIST_HEAD(, shm_mapping) *shm_dictionary;
static struct sx shm_dict_lock;
static struct mtx shm_timestamp_lock;
static u_long shm_hash;
static struct unrhdr64 shm_ino_unr;
static dev_t shm_dev_ino;

#define	SHM_HASH(fnv)	(&shm_dictionary[(fnv) & shm_hash])

static void	shm_init(void *arg);
static void	shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd);
static struct shmfd *shm_lookup(char *path, Fnv32_t fnv);
static int	shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred);
static int	shm_dotruncate_locked(struct shmfd *shmfd, off_t length,
    void *rl_cookie);
static int	shm_copyin_path(struct thread *td, const char *userpath_in,
    char **path_out);

static fo_rdwr_t	shm_read;
static fo_rdwr_t	shm_write;
static fo_truncate_t	shm_truncate;
static fo_ioctl_t	shm_ioctl;
static fo_stat_t	shm_stat;
static fo_close_t	shm_close;
static fo_chmod_t	shm_chmod;
static fo_chown_t	shm_chown;
static fo_seek_t	shm_seek;
static fo_fill_kinfo_t	shm_fill_kinfo;
static fo_mmap_t	shm_mmap;
static fo_get_seals_t	shm_get_seals;
static fo_add_seals_t	shm_add_seals;
static fo_fallocate_t	shm_fallocate;

/* File descriptor operations. */
struct fileops shm_ops = {
	.fo_read = shm_read,
	.fo_write = shm_write,
	.fo_truncate = shm_truncate,
	.fo_ioctl = shm_ioctl,
	.fo_poll = invfo_poll,
	.fo_kqfilter = invfo_kqfilter,
	.fo_stat = shm_stat,
	.fo_close = shm_close,
	.fo_chmod = shm_chmod,
	.fo_chown = shm_chown,
	.fo_sendfile = vn_sendfile,
	.fo_seek = shm_seek,
	.fo_fill_kinfo = shm_fill_kinfo,
	.fo_mmap = shm_mmap,
	.fo_get_seals = shm_get_seals,
	.fo_add_seals = shm_add_seals,
	.fo_fallocate = shm_fallocate,
	.fo_flags = DFLAG_PASSABLE | DFLAG_SEEKABLE
};

FEATURE(posix_shm, "POSIX shared memory");

static int
uiomove_object_page(vm_object_t obj, size_t len, struct uio *uio)
{
	vm_page_t m;
	vm_pindex_t idx;
	size_t tlen;
	int error, offset, rv;

	idx = OFF_TO_IDX(uio->uio_offset);
	offset = uio->uio_offset & PAGE_MASK;
	tlen = MIN(PAGE_SIZE - offset, len);

	rv = vm_page_grab_valid_unlocked(&m, obj, idx,
	    VM_ALLOC_SBUSY | VM_ALLOC_IGN_SBUSY | VM_ALLOC_NOCREAT);
	if (rv == VM_PAGER_OK)
		goto found;

	/*
	 * Read I/O without either a corresponding resident page or swap
	 * page: use zero_region.  This is intended to avoid instantiating
	 * pages on read from a sparse region.
	 */
	VM_OBJECT_WLOCK(obj);
	m = vm_page_lookup(obj, idx);
	if (uio->uio_rw == UIO_READ && m == NULL &&
	    !vm_pager_has_page(obj, idx, NULL, NULL)) {
		VM_OBJECT_WUNLOCK(obj);
		return (uiomove(__DECONST(void *, zero_region), tlen, uio));
	}

	/*
	 * Although the tmpfs vnode lock is held here, it is
	 * nonetheless safe to sleep waiting for a free page.  The
	 * pageout daemon does not need to acquire the tmpfs vnode
	 * lock to page out tobj's pages because tobj is a OBJT_SWAP
	 * type object.
	 */
	rv = vm_page_grab_valid(&m, obj, idx,
	    VM_ALLOC_NORMAL | VM_ALLOC_SBUSY | VM_ALLOC_IGN_SBUSY);
	if (rv != VM_PAGER_OK) {
		VM_OBJECT_WUNLOCK(obj);
		printf("uiomove_object: vm_obj %p idx %jd pager error %d\n",
		    obj, idx, rv);
		return (EIO);
	}
	VM_OBJECT_WUNLOCK(obj);

found:
	error = uiomove_fromphys(&m, offset, tlen, uio);
	if (uio->uio_rw == UIO_WRITE && error == 0)
		vm_page_set_dirty(m);
	vm_page_activate(m);
	vm_page_sunbusy(m);

	return (error);
}

int
uiomove_object(vm_object_t obj, off_t obj_size, struct uio *uio)
{
	ssize_t resid;
	size_t len;
	int error;

	error = 0;
	while ((resid = uio->uio_resid) > 0) {
		if (obj_size <= uio->uio_offset)
			break;
		len = MIN(obj_size - uio->uio_offset, resid);
		if (len == 0)
			break;
		error = uiomove_object_page(obj, len, uio);
		if (error != 0 || resid == uio->uio_resid)
			break;
	}
	return (error);
}

static int
shm_seek(struct file *fp, off_t offset, int whence, struct thread *td)
{
	struct shmfd *shmfd;
	off_t foffset;
	int error;

	shmfd = fp->f_data;
	foffset = foffset_lock(fp, 0);
	error = 0;
	switch (whence) {
	case L_INCR:
		if (foffset < 0 ||
		    (offset > 0 && foffset > OFF_MAX - offset)) {
			error = EOVERFLOW;
			break;
		}
		offset += foffset;
		break;
	case L_XTND:
		if (offset > 0 && shmfd->shm_size > OFF_MAX - offset) {
			error = EOVERFLOW;
			break;
		}
		offset += shmfd->shm_size;
		break;
	case L_SET:
		break;
	default:
		error = EINVAL;
	}
	if (error == 0) {
		if (offset < 0 || offset > shmfd->shm_size)
			error = EINVAL;
		else
			td->td_uretoff.tdu_off = offset;
	}
	foffset_unlock(fp, offset, error != 0 ? FOF_NOUPDATE : 0);
	return (error);
}

static int
shm_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{
	struct shmfd *shmfd;
	void *rl_cookie;
	int error;

	shmfd = fp->f_data;
#ifdef MAC
	error = mac_posixshm_check_read(active_cred, fp->f_cred, shmfd);
	if (error)
		return (error);
#endif
	foffset_lock_uio(fp, uio, flags);
	rl_cookie = rangelock_rlock(&shmfd->shm_rl, uio->uio_offset,
	    uio->uio_offset + uio->uio_resid, &shmfd->shm_mtx);
	error = uiomove_object(shmfd->shm_object, shmfd->shm_size, uio);
	rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
	foffset_unlock_uio(fp, uio, flags);
	return (error);
}

static int
shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{
	struct shmfd *shmfd;
	void *rl_cookie;
	int error;

	shmfd = fp->f_data;
#ifdef MAC
	error = mac_posixshm_check_write(active_cred, fp->f_cred, shmfd);
	if (error)
		return (error);
#endif
	foffset_lock_uio(fp, uio, flags);
	if ((flags & FOF_OFFSET) == 0) {
		rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
		    &shmfd->shm_mtx);
	} else {
		rl_cookie = rangelock_wlock(&shmfd->shm_rl, uio->uio_offset,
		    uio->uio_offset + uio->uio_resid, &shmfd->shm_mtx);
	}
	if ((shmfd->shm_seals & F_SEAL_WRITE) != 0)
		error = EPERM;
	else
		error = uiomove_object(shmfd->shm_object, shmfd->shm_size, uio);
	rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
	foffset_unlock_uio(fp, uio, flags);
	return (error);
}

static int
shm_truncate(struct file *fp, off_t length, struct ucred *active_cred,
    struct thread *td)
{
	struct shmfd *shmfd;
#ifdef MAC
	int error;
#endif

	shmfd = fp->f_data;
#ifdef MAC
	error = mac_posixshm_check_truncate(active_cred, fp->f_cred, shmfd);
	if (error)
		return (error);
#endif
	return (shm_dotruncate(shmfd, length));
}

int
shm_ioctl(struct file *fp, u_long com, void *data, struct ucred *active_cred,
    struct thread *td)
{

	switch (com) {
	case FIONBIO:
	case FIOASYNC:
		/*
		 * Allow fcntl(fd, F_SETFL, O_NONBLOCK) to work,
		 * just like it would on an unlinked regular file
		 */
		return (0);
	default:
		return (ENOTTY);
	}
}

static int
shm_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
    struct thread *td)
{
	struct shmfd *shmfd;
#ifdef MAC
	int error;
#endif

	shmfd = fp->f_data;

#ifdef MAC
	error = mac_posixshm_check_stat(active_cred, fp->f_cred, shmfd);
	if (error)
		return (error);
#endif
	
	/*
	 * Attempt to return sanish values for fstat() on a memory file
	 * descriptor.
	 */
	bzero(sb, sizeof(*sb));
	sb->st_blksize = PAGE_SIZE;
	sb->st_size = shmfd->shm_size;
	sb->st_blocks = howmany(sb->st_size, sb->st_blksize);
	mtx_lock(&shm_timestamp_lock);
	sb->st_atim = shmfd->shm_atime;
	sb->st_ctim = shmfd->shm_ctime;
	sb->st_mtim = shmfd->shm_mtime;
	sb->st_birthtim = shmfd->shm_birthtime;
	sb->st_mode = S_IFREG | shmfd->shm_mode;		/* XXX */
	sb->st_uid = shmfd->shm_uid;
	sb->st_gid = shmfd->shm_gid;
	mtx_unlock(&shm_timestamp_lock);
	sb->st_dev = shm_dev_ino;
	sb->st_ino = shmfd->shm_ino;
	sb->st_nlink = shmfd->shm_object->ref_count;

	return (0);
}

static int
shm_close(struct file *fp, struct thread *td)
{
	struct shmfd *shmfd;

	shmfd = fp->f_data;
	fp->f_data = NULL;
	shm_drop(shmfd);

	return (0);
}

static int
shm_copyin_path(struct thread *td, const char *userpath_in, char **path_out) {
	int error;
	char *path;
	const char *pr_path;
	size_t pr_pathlen;

	path = malloc(MAXPATHLEN, M_SHMFD, M_WAITOK);
	pr_path = td->td_ucred->cr_prison->pr_path;

	/* Construct a full pathname for jailed callers. */
	pr_pathlen = strcmp(pr_path, "/") ==
	    0 ? 0 : strlcpy(path, pr_path, MAXPATHLEN);
	error = copyinstr(userpath_in, path + pr_pathlen,
	    MAXPATHLEN - pr_pathlen, NULL);
	if (error != 0)
		goto out;

#ifdef KTRACE
	if (KTRPOINT(curthread, KTR_NAMEI))
		ktrnamei(path);
#endif

	/* Require paths to start with a '/' character. */
	if (path[pr_pathlen] != '/') {
		error = EINVAL;
		goto out;
	}

	*path_out = path;

out:
	if (error != 0)
		free(path, M_SHMFD);

	return (error);
}

static int
shm_dotruncate_locked(struct shmfd *shmfd, off_t length, void *rl_cookie)
{
	vm_object_t object;
	vm_page_t m;
	vm_pindex_t idx, nobjsize;
	vm_ooffset_t delta;
	int base, rv;

	KASSERT(length >= 0, ("shm_dotruncate: length < 0"));
	object = shmfd->shm_object;
	VM_OBJECT_ASSERT_WLOCKED(object);
	rangelock_cookie_assert(rl_cookie, RA_WLOCKED);
	if (length == shmfd->shm_size)
		return (0);
	nobjsize = OFF_TO_IDX(length + PAGE_MASK);

	/* Are we shrinking?  If so, trim the end. */
	if (length < shmfd->shm_size) {
		if ((shmfd->shm_seals & F_SEAL_SHRINK) != 0)
			return (EPERM);

		/*
		 * Disallow any requests to shrink the size if this
		 * object is mapped into the kernel.
		 */
		if (shmfd->shm_kmappings > 0)
			return (EBUSY);

		/*
		 * Zero the truncated part of the last page.
		 */
		base = length & PAGE_MASK;
		if (base != 0) {
			idx = OFF_TO_IDX(length);
retry:
			m = vm_page_grab(object, idx, VM_ALLOC_NOCREAT);
			if (m != NULL) {
				MPASS(vm_page_all_valid(m));
			} else if (vm_pager_has_page(object, idx, NULL, NULL)) {
				m = vm_page_alloc(object, idx,
				    VM_ALLOC_NORMAL | VM_ALLOC_WAITFAIL);
				if (m == NULL)
					goto retry;
				vm_object_pip_add(object, 1);
				VM_OBJECT_WUNLOCK(object);
				rv = vm_pager_get_pages(object, &m, 1, NULL,
				    NULL);
				VM_OBJECT_WLOCK(object);
				vm_object_pip_wakeup(object);
				if (rv == VM_PAGER_OK) {
					/*
					 * Since the page was not resident,
					 * and therefore not recently
					 * accessed, immediately enqueue it
					 * for asynchronous laundering.  The
					 * current operation is not regarded
					 * as an access.
					 */
					vm_page_launder(m);
				} else {
					vm_page_free(m);
					VM_OBJECT_WUNLOCK(object);
					return (EIO);
				}
			}
			if (m != NULL) {
				pmap_zero_page_area(m, base, PAGE_SIZE - base);
				KASSERT(vm_page_all_valid(m),
				    ("shm_dotruncate: page %p is invalid", m));
				vm_page_set_dirty(m);
				vm_page_xunbusy(m);
			}
		}
		delta = IDX_TO_OFF(object->size - nobjsize);

		/* Toss in memory pages. */
		if (nobjsize < object->size)
			vm_object_page_remove(object, nobjsize, object->size,
			    0);

		/* Toss pages from swap. */
		if (object->type == OBJT_SWAP)
			swap_pager_freespace(object, nobjsize, delta);

		/* Free the swap accounted for shm */
		swap_release_by_cred(delta, object->cred);
		object->charge -= delta;
	} else {
		if ((shmfd->shm_seals & F_SEAL_GROW) != 0)
			return (EPERM);

		/* Try to reserve additional swap space. */
		delta = IDX_TO_OFF(nobjsize - object->size);
		if (!swap_reserve_by_cred(delta, object->cred))
			return (ENOMEM);
		object->charge += delta;
	}
	shmfd->shm_size = length;
	mtx_lock(&shm_timestamp_lock);
	vfs_timestamp(&shmfd->shm_ctime);
	shmfd->shm_mtime = shmfd->shm_ctime;
	mtx_unlock(&shm_timestamp_lock);
	object->size = nobjsize;
	return (0);
}

int
shm_dotruncate(struct shmfd *shmfd, off_t length)
{
	void *rl_cookie;
	int error;

	rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
	    &shmfd->shm_mtx);
	VM_OBJECT_WLOCK(shmfd->shm_object);
	error = shm_dotruncate_locked(shmfd, length, rl_cookie);
	VM_OBJECT_WUNLOCK(shmfd->shm_object);
	rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
	return (error);
}

/*
 * shmfd object management including creation and reference counting
 * routines.
 */
struct shmfd *
shm_alloc(struct ucred *ucred, mode_t mode)
{
	struct shmfd *shmfd;

	shmfd = malloc(sizeof(*shmfd), M_SHMFD, M_WAITOK | M_ZERO);
	shmfd->shm_size = 0;
	shmfd->shm_uid = ucred->cr_uid;
	shmfd->shm_gid = ucred->cr_gid;
	shmfd->shm_mode = mode;
	shmfd->shm_object = vm_pager_allocate(OBJT_SWAP, NULL,
	    shmfd->shm_size, VM_PROT_DEFAULT, 0, ucred);
	KASSERT(shmfd->shm_object != NULL, ("shm_create: vm_pager_allocate"));
	vfs_timestamp(&shmfd->shm_birthtime);
	shmfd->shm_atime = shmfd->shm_mtime = shmfd->shm_ctime =
	    shmfd->shm_birthtime;
	shmfd->shm_ino = alloc_unr64(&shm_ino_unr);
	refcount_init(&shmfd->shm_refs, 1);
	mtx_init(&shmfd->shm_mtx, "shmrl", NULL, MTX_DEF);
	rangelock_init(&shmfd->shm_rl);
#ifdef MAC
	mac_posixshm_init(shmfd);
	mac_posixshm_create(ucred, shmfd);
#endif

	return (shmfd);
}

struct shmfd *
shm_hold(struct shmfd *shmfd)
{

	refcount_acquire(&shmfd->shm_refs);
	return (shmfd);
}

void
shm_drop(struct shmfd *shmfd)
{

	if (refcount_release(&shmfd->shm_refs)) {
#ifdef MAC
		mac_posixshm_destroy(shmfd);
#endif
		rangelock_destroy(&shmfd->shm_rl);
		mtx_destroy(&shmfd->shm_mtx);
		vm_object_deallocate(shmfd->shm_object);
		free(shmfd, M_SHMFD);
	}
}

/*
 * Determine if the credentials have sufficient permissions for a
 * specified combination of FREAD and FWRITE.
 */
int
shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags)
{
	accmode_t accmode;
	int error;

	accmode = 0;
	if (flags & FREAD)
		accmode |= VREAD;
	if (flags & FWRITE)
		accmode |= VWRITE;
	mtx_lock(&shm_timestamp_lock);
	error = vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid, shmfd->shm_gid,
	    accmode, ucred, NULL);
	mtx_unlock(&shm_timestamp_lock);
	return (error);
}

/*
 * Dictionary management.  We maintain an in-kernel dictionary to map
 * paths to shmfd objects.  We use the FNV hash on the path to store
 * the mappings in a hash table.
 */
static void
shm_init(void *arg)
{

	mtx_init(&shm_timestamp_lock, "shm timestamps", NULL, MTX_DEF);
	sx_init(&shm_dict_lock, "shm dictionary");
	shm_dictionary = hashinit(1024, M_SHMFD, &shm_hash);
	new_unrhdr64(&shm_ino_unr, 1);
	shm_dev_ino = devfs_alloc_cdp_inode();
	KASSERT(shm_dev_ino > 0, ("shm dev inode not initialized"));
}
SYSINIT(shm_init, SI_SUB_SYSV_SHM, SI_ORDER_ANY, shm_init, NULL);

static struct shmfd *
shm_lookup(char *path, Fnv32_t fnv)
{
	struct shm_mapping *map;

	LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
		if (map->sm_fnv != fnv)
			continue;
		if (strcmp(map->sm_path, path) == 0)
			return (map->sm_shmfd);
	}

	return (NULL);
}

static void
shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd)
{
	struct shm_mapping *map;

	map = malloc(sizeof(struct shm_mapping), M_SHMFD, M_WAITOK);
	map->sm_path = path;
	map->sm_fnv = fnv;
	map->sm_shmfd = shm_hold(shmfd);
	shmfd->shm_path = path;
	LIST_INSERT_HEAD(SHM_HASH(fnv), map, sm_link);
}

static int
shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred)
{
	struct shm_mapping *map;
	int error;

	LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
		if (map->sm_fnv != fnv)
			continue;
		if (strcmp(map->sm_path, path) == 0) {
#ifdef MAC
			error = mac_posixshm_check_unlink(ucred, map->sm_shmfd);
			if (error)
				return (error);
#endif
			error = shm_access(map->sm_shmfd, ucred,
			    FREAD | FWRITE);
			if (error)
				return (error);
			map->sm_shmfd->shm_path = NULL;
			LIST_REMOVE(map, sm_link);
			shm_drop(map->sm_shmfd);
			free(map->sm_path, M_SHMFD);
			free(map, M_SHMFD);
			return (0);
		}
	}

	return (ENOENT);
}

int
kern_shm_open2(struct thread *td, const char *userpath, int flags, mode_t mode,
    int shmflags, struct filecaps *fcaps, const char *name __unused)
{
	struct filedesc *fdp;
	struct shmfd *shmfd;
	struct file *fp;
	char *path;
	void *rl_cookie;
	Fnv32_t fnv;
	mode_t cmode;
	int error, fd, initial_seals;

	if ((shmflags & ~SHM_ALLOW_SEALING) != 0)
		return (EINVAL);

	initial_seals = F_SEAL_SEAL;
	if ((shmflags & SHM_ALLOW_SEALING) != 0)
		initial_seals &= ~F_SEAL_SEAL;

#ifdef CAPABILITY_MODE
	/*
	 * shm_open(2) is only allowed for anonymous objects.
	 */
	if (IN_CAPABILITY_MODE(td) && (userpath != SHM_ANON))
		return (ECAPMODE);
#endif

	AUDIT_ARG_FFLAGS(flags);
	AUDIT_ARG_MODE(mode);

	if ((flags & O_ACCMODE) != O_RDONLY && (flags & O_ACCMODE) != O_RDWR)
		return (EINVAL);

	if ((flags & ~(O_ACCMODE | O_CREAT | O_EXCL | O_TRUNC | O_CLOEXEC)) != 0)
		return (EINVAL);

	/*
	 * Currently only F_SEAL_SEAL may be set when creating or opening shmfd.
	 * If the decision is made later to allow additional seals, care must be
	 * taken below to ensure that the seals are properly set if the shmfd
	 * already existed -- this currently assumes that only F_SEAL_SEAL can
	 * be set and doesn't take further precautions to ensure the validity of
	 * the seals being added with respect to current mappings.
	 */
	if ((initial_seals & ~F_SEAL_SEAL) != 0)
		return (EINVAL);

	fdp = td->td_proc->p_fd;
	cmode = (mode & ~fdp->fd_cmask) & ACCESSPERMS;

	/*
	 * shm_open(2) created shm should always have O_CLOEXEC set, as mandated
	 * by POSIX.  We allow it to be unset here so that an in-kernel
	 * interface may be written as a thin layer around shm, optionally not
	 * setting CLOEXEC.  For shm_open(2), O_CLOEXEC is set unconditionally
	 * in sys_shm_open() to keep this implementation compliant.
	 */
	error = falloc_caps(td, &fp, &fd, flags & O_CLOEXEC, fcaps);
	if (error)
		return (error);

	/* A SHM_ANON path pointer creates an anonymous object. */
	if (userpath == SHM_ANON) {
		/* A read-only anonymous object is pointless. */
		if ((flags & O_ACCMODE) == O_RDONLY) {
			fdclose(td, fp, fd);
			fdrop(fp, td);
			return (EINVAL);
		}
		shmfd = shm_alloc(td->td_ucred, cmode);
		shmfd->shm_seals = initial_seals;
	} else {
		error = shm_copyin_path(td, userpath, &path);
		if (error != 0) {
			fdclose(td, fp, fd);
			fdrop(fp, td);
			return (error);
		}

		AUDIT_ARG_UPATH1_CANON(path);
		fnv = fnv_32_str(path, FNV1_32_INIT);
		sx_xlock(&shm_dict_lock);
		shmfd = shm_lookup(path, fnv);
		if (shmfd == NULL) {
			/* Object does not yet exist, create it if requested. */
			if (flags & O_CREAT) {
#ifdef MAC
				error = mac_posixshm_check_create(td->td_ucred,
				    path);
				if (error == 0) {
#endif
					shmfd = shm_alloc(td->td_ucred, cmode);
					shmfd->shm_seals = initial_seals;
					shm_insert(path, fnv, shmfd);
#ifdef MAC
				}
#endif
			} else {
				free(path, M_SHMFD);
				error = ENOENT;
			}
		} else {
			rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
			    &shmfd->shm_mtx);

			/*
			 * kern_shm_open() likely shouldn't ever error out on
			 * trying to set a seal that already exists, unlike
			 * F_ADD_SEALS.  This would break terribly as
			 * shm_open(2) actually sets F_SEAL_SEAL to maintain
			 * historical behavior where the underlying file could
			 * not be sealed.
			 */
			initial_seals &= ~shmfd->shm_seals;

			/*
			 * Object already exists, obtain a new
			 * reference if requested and permitted.
			 */
			free(path, M_SHMFD);

			/*
			 * initial_seals can't set additional seals if we've
			 * already been set F_SEAL_SEAL.  If F_SEAL_SEAL is set,
			 * then we've already removed that one from
			 * initial_seals.  This is currently redundant as we
			 * only allow setting F_SEAL_SEAL at creation time, but
			 * it's cheap to check and decreases the effort required
			 * to allow additional seals.
			 */
			if ((shmfd->shm_seals & F_SEAL_SEAL) != 0 &&
			    initial_seals != 0)
				error = EPERM;
			else if ((flags & (O_CREAT | O_EXCL)) ==
			    (O_CREAT | O_EXCL))
				error = EEXIST;
			else {
#ifdef MAC
				error = mac_posixshm_check_open(td->td_ucred,
				    shmfd, FFLAGS(flags & O_ACCMODE));
				if (error == 0)
#endif
				error = shm_access(shmfd, td->td_ucred,
				    FFLAGS(flags & O_ACCMODE));
			}

			/*
			 * Truncate the file back to zero length if
			 * O_TRUNC was specified and the object was
			 * opened with read/write.
			 */
			if (error == 0 &&
			    (flags & (O_ACCMODE | O_TRUNC)) ==
			    (O_RDWR | O_TRUNC)) {
				VM_OBJECT_WLOCK(shmfd->shm_object);
#ifdef MAC
				error = mac_posixshm_check_truncate(
					td->td_ucred, fp->f_cred, shmfd);
				if (error == 0)
#endif
					error = shm_dotruncate_locked(shmfd, 0,
					    rl_cookie);
				VM_OBJECT_WUNLOCK(shmfd->shm_object);
			}
			if (error == 0) {
				/*
				 * Currently we only allow F_SEAL_SEAL to be
				 * set initially.  As noted above, this would
				 * need to be reworked should that change.
				 */
				shmfd->shm_seals |= initial_seals;
				shm_hold(shmfd);
			}
			rangelock_unlock(&shmfd->shm_rl, rl_cookie,
			    &shmfd->shm_mtx);
		}
		sx_xunlock(&shm_dict_lock);

		if (error) {
			fdclose(td, fp, fd);
			fdrop(fp, td);
			return (error);
		}
	}

	finit(fp, FFLAGS(flags & O_ACCMODE), DTYPE_SHM, shmfd, &shm_ops);

	td->td_retval[0] = fd;
	fdrop(fp, td);

	return (0);
}

/* System calls. */
#ifdef COMPAT_FREEBSD12
int
freebsd12_shm_open(struct thread *td, struct freebsd12_shm_open_args *uap)
{

	return (kern_shm_open(td, uap->path, uap->flags | O_CLOEXEC,
	    uap->mode, NULL));
}
#endif

int
sys_shm_unlink(struct thread *td, struct shm_unlink_args *uap)
{
	char *path;
	Fnv32_t fnv;
	int error;

	error = shm_copyin_path(td, uap->path, &path);
	if (error != 0)
		return (error);

	AUDIT_ARG_UPATH1_CANON(path);
	fnv = fnv_32_str(path, FNV1_32_INIT);
	sx_xlock(&shm_dict_lock);
	error = shm_remove(path, fnv, td->td_ucred);
	sx_xunlock(&shm_dict_lock);
	free(path, M_SHMFD);

	return (error);
}

int
sys_shm_rename(struct thread *td, struct shm_rename_args *uap)
{
	char *path_from = NULL, *path_to = NULL;
	Fnv32_t fnv_from, fnv_to;
	struct shmfd *fd_from;
	struct shmfd *fd_to;
	int error;
	int flags;

	flags = uap->flags;
	AUDIT_ARG_FFLAGS(flags);

	/*
	 * Make sure the user passed only valid flags.
	 * If you add a new flag, please add a new term here.
	 */
	if ((flags & ~(
	    SHM_RENAME_NOREPLACE |
	    SHM_RENAME_EXCHANGE
	    )) != 0) {
		error = EINVAL;
		goto out;
	}

	/*
	 * EXCHANGE and NOREPLACE don't quite make sense together. Let's
	 * force the user to choose one or the other.
	 */
	if ((flags & SHM_RENAME_NOREPLACE) != 0 &&
	    (flags & SHM_RENAME_EXCHANGE) != 0) {
		error = EINVAL;