/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2019 Allan Jude <allanjude@FreeBSD.org>
 *
 * 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.
 *
 * $FreeBSD$
 */

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/jail.h>
#include <sys/module.h>
#include <sys/priv.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/ucred.h>
#include <sys/vnode.h>

#include <security/mac/mac_policy.h>

SYSCTL_DECL(_security_mac);

static SYSCTL_NODE(_security_mac, OID_AUTO, fileapi, CTLFLAG_RW, 0,
    "mac_fileapi policy controls");

static int fileapi_enabled = 1;
SYSCTL_INT(_security_mac_fileapi, OID_AUTO, enabled, CTLFLAG_RWTUN,
    &fileapi_enabled, 0, "Enable mac_fileapi policy");

static int fileapi_uid = 1041;
SYSCTL_INT(_security_mac_fileapi, OID_AUTO, uid, CTLFLAG_RWTUN,
    &fileapi_uid, 0, "User id for fileapi user");

static int
fileapi_priv_grant(struct ucred *cred, int priv)
{

        if (fileapi_enabled &&
            cred->cr_prison->pr_id != 0 &&
            cred->cr_uid == fileapi_uid) {
                switch (priv) {
                case PRIV_VFS_CHOWN:
                case PRIV_VFS_CHROOT:
                case PRIV_VFS_ADMIN:
                        return (0);
                default:
                        break;
                }
        }
        return (EPERM);
}

static int
fileapi_vnode_check_setowner(struct ucred *cred, struct vnode *vp,
    struct label *vplabel, uid_t uid, gid_t gid)
{
        int error;
        struct vattr va;

        if (fileapi_enabled &&
            cred->cr_prison->pr_id != 0 &&
            cred->cr_uid == fileapi_uid) {
                /*
                 * Ensure the file we are chown()ing is not owned by an
                 * unprivileged user.
                 */
                /* Get vnode attributes */
                error = VOP_GETATTR(vp, &va, cred);
                if (error)
                        return (error);

                if (va.va_uid == 0)
                        return (EPERM);
        }

        return (0);
}

static struct mac_policy_ops fileapi_ops =
{
        .mpo_priv_grant = fileapi_priv_grant,
        .mpo_vnode_check_setowner = fileapi_vnode_check_setowner,
};

MAC_POLICY_SET(&fileapi_ops, mac_fileapi, "MAC/fileapi",
    MPC_LOADTIME_FLAG_UNLOADOK, NULL);