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mirror_zfs/module/os/freebsd/spl/spl_policy.c
Rob Norris c8fa39b46c
cred: properly pass and test creds on other threads (#17273) 
### Background

Various admin operations will be invoked by some userspace task, but the
work will be done on a separate kernel thread at a later time. Snapshots
are an example, which are triggered through zfs_ioc_snapshot() ->
dsl_dataset_snapshot(), but the actual work is from a task dispatched to
dp_sync_taskq.

Many such tasks end up in dsl_enforce_ds_ss_limits(), where various
limits and permissions are enforced. Among other things, it is necessary
to ensure that the invoking task (that is, the user) has permission to
do things. We can't simply check if the running task has permission; it
is a privileged kernel thread, which can do anything.

However, in the general case it's not safe to simply query the task for
its permissions at the check time, as the task may not exist any more,
or its permissions may have changed since it was first invoked. So
instead, we capture the permissions by saving CRED() in the user task,
and then using it for the check through the secpolicy_* functions.

### Current implementation

The current code calls CRED() to get the credential, which gets a
pointer to the cred_t inside the current task and passes it to the
worker task. However, it doesn't take a reference to the cred_t, and so
expects that it won't change, and that the task continues to exist. In
practice that is always the case, because we don't let the calling task
return from the kernel until the work is done.

For Linux, we also take a reference to the current task, because the
Linux credential APIs for the most part do not check an arbitrary
credential, but rather, query what a task can do. See
secpolicy_zfs_proc(). Again, we don't take a reference on the task, just
a pointer to it.

### Changes

We change to calling crhold() on the task credential, and crfree() when
we're done with it. This ensures it stays alive and unchanged for the
duration of the call.

On the Linux side, we change the main policy checking function
priv_policy_ns() to use override_creds()/revert_creds() if necessary to
make the provided credential active in the current task, allowing the
standard task-permission APIs to do the needed check. Since the task
pointer is no longer required, this lets us entirely remove
secpolicy_zfs_proc() and the need to carry a task pointer around as
well.

Sponsored-by: https://despairlabs.com/sponsor/

Signed-off-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Pavel Snajdr <snajpa@snajpa.net>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Kyle Evans <kevans@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
2025-04-29 16:27:48 -07:00

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// SPDX-License-Identifier: BSD-2-Clause
/*
* Copyright (c) 2007 Pawel Jakub Dawidek <pjd@FreeBSD.org>
* All rights reserved.
*
* 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 AUTHORS 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 AUTHORS 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.
*/
#include <sys/types.h>
#include <sys/param.h>
#include <sys/priv.h>
#include <sys/vnode.h>
#include <sys/mntent.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/jail.h>
#include <sys/policy.h>
#include <sys/zfs_vfsops.h>
#include <sys/zfs_znode.h>
int
secpolicy_nfs(cred_t *cr)
{
return (priv_check_cred(cr, PRIV_NFS_DAEMON));
}
int
secpolicy_zfs(cred_t *cr)
{
return (priv_check_cred(cr, PRIV_VFS_MOUNT));
}
int
secpolicy_sys_config(cred_t *cr, int checkonly __unused)
{
return (priv_check_cred(cr, PRIV_ZFS_POOL_CONFIG));
}
int
secpolicy_zinject(cred_t *cr)
{
return (priv_check_cred(cr, PRIV_ZFS_INJECT));
}
int
secpolicy_fs_unmount(cred_t *cr, struct mount *vfsp __unused)
{
return (priv_check_cred(cr, PRIV_VFS_UNMOUNT));
}
int
secpolicy_fs_owner(struct mount *mp, cred_t *cr)
{
if (zfs_super_owner) {
if (cr->cr_uid == mp->mnt_cred->cr_uid &&
cr->cr_prison == mp->mnt_cred->cr_prison) {
return (0);
}
}
return (EPERM);
}
/*
* This check is done in kern_link(), so we could just return 0 here.
*/
extern int hardlink_check_uid;
int
secpolicy_basic_link(vnode_t *vp, cred_t *cr)
{
if (!hardlink_check_uid)
return (0);
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
return (priv_check_cred(cr, PRIV_VFS_LINK));
}
int
secpolicy_vnode_stky_modify(cred_t *cr)
{
return (EPERM);
}
int
secpolicy_vnode_remove(vnode_t *vp, cred_t *cr)
{
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
return (priv_check_cred(cr, PRIV_VFS_ADMIN));
}
int
secpolicy_vnode_access(cred_t *cr, vnode_t *vp, uid_t owner, accmode_t accmode)
{
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
if ((accmode & VREAD) && priv_check_cred(cr, PRIV_VFS_READ) != 0)
return (EACCES);
if ((accmode & VWRITE) &&
priv_check_cred(cr, PRIV_VFS_WRITE) != 0) {
return (EACCES);
}
if (accmode & VEXEC) {
if (vp->v_type == VDIR) {
if (priv_check_cred(cr, PRIV_VFS_LOOKUP) != 0)
return (EACCES);
} else {
if (priv_check_cred(cr, PRIV_VFS_EXEC) != 0)
return (EACCES);
}
}
return (0);
}
/*
* Like secpolicy_vnode_access() but we get the actual wanted mode and the
* current mode of the file, not the missing bits.
*/
int
secpolicy_vnode_access2(cred_t *cr, vnode_t *vp, uid_t owner,
accmode_t curmode, accmode_t wantmode)
{
accmode_t mode;
mode = ~curmode & wantmode;
if (mode == 0)
return (0);
return (secpolicy_vnode_access(cr, vp, owner, mode));
}
int
secpolicy_vnode_any_access(cred_t *cr, vnode_t *vp, uid_t owner)
{
static int privs[] = {
PRIV_VFS_ADMIN,
PRIV_VFS_READ,
PRIV_VFS_WRITE,
PRIV_VFS_EXEC,
PRIV_VFS_LOOKUP
};
int i;
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
/* Same as secpolicy_vnode_setdac */
if (owner == cr->cr_uid)
return (0);
for (i = 0; i < sizeof (privs)/sizeof (int); i++) {
int priv;
switch (priv = privs[i]) {
case PRIV_VFS_EXEC:
if (vp->v_type == VDIR)
continue;
break;
case PRIV_VFS_LOOKUP:
if (vp->v_type != VDIR)
continue;
break;
}
if (priv_check_cred(cr, priv) == 0)
return (0);
}
return (EPERM);
}
int
secpolicy_vnode_setdac(vnode_t *vp, cred_t *cr, uid_t owner)
{
if (owner == cr->cr_uid)
return (0);
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
return (priv_check_cred(cr, PRIV_VFS_ADMIN));
}
int
secpolicy_vnode_setattr(cred_t *cr, vnode_t *vp, struct vattr *vap,
const struct vattr *ovap, int flags,
int unlocked_access(void *, int, cred_t *), void *node)
{
int mask = vap->va_mask;
int error;
if (mask & AT_SIZE) {
if (vp->v_type == VDIR)
return (EISDIR);
error = unlocked_access(node, VWRITE, cr);
if (error)
return (error);
}
if (mask & AT_MODE) {
/*
* If not the owner of the file then check privilege
* for two things: the privilege to set the mode at all
* and, if we're setting setuid, we also need permissions
* to add the set-uid bit, if we're not the owner.
* In the specific case of creating a set-uid root
* file, we need even more permissions.
*/
error = secpolicy_vnode_setdac(vp, cr, ovap->va_uid);
if (error)
return (error);
error = secpolicy_setid_setsticky_clear(vp, vap, ovap, cr);
if (error)
return (error);
} else {
vap->va_mode = ovap->va_mode;
}
if (mask & (AT_UID | AT_GID)) {
error = secpolicy_vnode_setdac(vp, cr, ovap->va_uid);
if (error)
return (error);
/*
* To change the owner of a file, or change the group of
* a file to a group of which we are not a member, the
* caller must have privilege.
*/
if (((mask & AT_UID) && vap->va_uid != ovap->va_uid) ||
((mask & AT_GID) && vap->va_gid != ovap->va_gid &&
!groupmember(vap->va_gid, cr))) {
if (secpolicy_fs_owner(vp->v_mount, cr) != 0) {
error = priv_check_cred(cr, PRIV_VFS_CHOWN);
if (error)
return (error);
}
}
if (((mask & AT_UID) && vap->va_uid != ovap->va_uid) ||
((mask & AT_GID) && vap->va_gid != ovap->va_gid)) {
secpolicy_setid_clear(vap, vp, cr);
}
}
if (mask & (AT_ATIME | AT_MTIME)) {
/*
* From utimes(2):
* If times is NULL, ... The caller must be the owner of
* the file, have permission to write the file, or be the
* super-user.
* If times is non-NULL, ... The caller must be the owner of
* the file or be the super-user.
*/
error = secpolicy_vnode_setdac(vp, cr, ovap->va_uid);
if (error && (vap->va_vaflags & VA_UTIMES_NULL))
error = unlocked_access(node, VWRITE, cr);
if (error)
return (error);
}
return (0);
}
int
secpolicy_vnode_create_gid(cred_t *cr)
{
return (EPERM);
}
int
secpolicy_vnode_setids_setgids(vnode_t *vp, cred_t *cr, gid_t gid)
{
if (groupmember(gid, cr))
return (0);
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
return (priv_check_cred(cr, PRIV_VFS_SETGID));
}
int
secpolicy_vnode_setid_retain(znode_t *zp, cred_t *cr,
boolean_t issuidroot __unused)
{
if (secpolicy_fs_owner(ZTOV(zp)->v_mount, cr) == 0)
return (0);
return (priv_check_cred(cr, PRIV_VFS_RETAINSUGID));
}
void
secpolicy_setid_clear(struct vattr *vap, vnode_t *vp, cred_t *cr)
{
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return;
if ((vap->va_mode & (S_ISUID | S_ISGID)) != 0) {
if (priv_check_cred(cr, PRIV_VFS_RETAINSUGID)) {
vap->va_mask |= AT_MODE;
vap->va_mode &= ~(S_ISUID|S_ISGID);
}
}
}
int
secpolicy_setid_setsticky_clear(vnode_t *vp, struct vattr *vap,
const struct vattr *ovap, cred_t *cr)
{
int error;
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
/*
* Privileged processes may set the sticky bit on non-directories,
* as well as set the setgid bit on a file with a group that the process
* is not a member of. Both of these are allowed in jail(8).
*/
if (vp->v_type != VDIR && (vap->va_mode & S_ISTXT)) {
if (priv_check_cred(cr, PRIV_VFS_STICKYFILE))
return (EFTYPE);
}
/*
* Check for privilege if attempting to set the
* group-id bit.
*/
if ((vap->va_mode & S_ISGID) != 0) {
error = secpolicy_vnode_setids_setgids(vp, cr, ovap->va_gid);
if (error)
return (error);
}
/*
* Deny setting setuid if we are not the file owner.
*/
if ((vap->va_mode & S_ISUID) && ovap->va_uid != cr->cr_uid) {
error = priv_check_cred(cr, PRIV_VFS_ADMIN);
if (error)
return (error);
}
return (0);
}
int
secpolicy_fs_mount(cred_t *cr, vnode_t *mvp, struct mount *vfsp)
{
return (priv_check_cred(cr, PRIV_VFS_MOUNT));
}
int
secpolicy_vnode_owner(vnode_t *vp, cred_t *cr, uid_t owner)
{
if (owner == cr->cr_uid)
return (0);
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
/* XXX: vfs_suser()? */
return (priv_check_cred(cr, PRIV_VFS_MOUNT_OWNER));
}
int
secpolicy_vnode_chown(vnode_t *vp, cred_t *cr, uid_t owner)
{
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
return (priv_check_cred(cr, PRIV_VFS_CHOWN));
}
void
secpolicy_fs_mount_clearopts(cred_t *cr, struct mount *vfsp)
{
if (priv_check_cred(cr, PRIV_VFS_MOUNT_NONUSER) != 0) {
MNT_ILOCK(vfsp);
vfsp->vfs_flag |= VFS_NOSETUID | MNT_USER;
vfs_clearmntopt(vfsp, MNTOPT_SETUID);
vfs_setmntopt(vfsp, MNTOPT_NOSETUID, NULL, 0);
MNT_IUNLOCK(vfsp);
}
}
/*
* Check privileges for setting xvattr attributes
*/
int
secpolicy_xvattr(vnode_t *vp, xvattr_t *xvap, uid_t owner, cred_t *cr,
vtype_t vtype)
{
if (secpolicy_fs_owner(vp->v_mount, cr) == 0)
return (0);
return (priv_check_cred(cr, PRIV_VFS_SYSFLAGS));
}
int
secpolicy_smb(cred_t *cr)
{
return (priv_check_cred(cr, PRIV_NETSMB));
}
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