/*      $NetBSD: secmodel_extensions_vfs.c,v 1.1 2023/04/22 13:54:19 riastradh Exp $    */

/*-
 * Copyright (c) 2011 Elad Efrat <elad@NetBSD.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.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: secmodel_extensions_vfs.c,v 1.1 2023/04/22 13:54:19 riastradh Exp $");

#include <sys/types.h>
#include <sys/param.h>

#include <sys/kauth.h>
#include <sys/vnode.h>

#include <secmodel/secmodel.h>
#include <secmodel/extensions/extensions.h>
#include <secmodel/extensions/extensions_impl.h>

static int dovfsusermount;
static int hardlink_check_uid;
static int hardlink_check_gid;

static kauth_listener_t l_system, l_vnode;

static int secmodel_extensions_system_cb(kauth_cred_t, kauth_action_t,
    void *, void *, void *, void *, void *);
static int secmodel_extensions_vnode_cb(kauth_cred_t, kauth_action_t,
    void *, void *, void *, void *, void *);

void
secmodel_extensions_vfs_start(void)
{

        l_system = kauth_listen_scope(KAUTH_SCOPE_SYSTEM,
            secmodel_extensions_system_cb, NULL);
        l_vnode = kauth_listen_scope(KAUTH_SCOPE_VNODE,
            secmodel_extensions_vnode_cb, NULL);
}

void
secmodel_extensions_vfs_stop(void)
{

        kauth_unlisten_scope(l_system);
        kauth_unlisten_scope(l_vnode);
}

void
secmodel_extensions_vfs_sysctl(struct sysctllog **clog,
    const struct sysctlnode *rnode)
{

        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "usermount",
                       SYSCTL_DESCR("Whether unprivileged users may mount "
                                    "filesystems"),
                       sysctl_extensions_user_handler, 0, &dovfsusermount, 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "hardlink_check_uid",
                       SYSCTL_DESCR("Whether unprivileged users can hardlink "\
                            "to files they don't own"),
                       sysctl_extensions_user_handler, 0,
                       &hardlink_check_uid, 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "hardlink_check_gid",
                       SYSCTL_DESCR("Whether unprivileged users can hardlink "\
                            "to files that are not in their " \
                            "group membership"),
                       sysctl_extensions_user_handler, 0,
                       &hardlink_check_gid, 0,
                       CTL_CREATE, CTL_EOL);

        /* Compatibility: vfs.generic.usermount */
        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_NODE, "generic",
                       SYSCTL_DESCR("Non-specific vfs related information"),
                       NULL, 0, NULL, 0,
                       CTL_VFS, VFS_GENERIC, CTL_EOL);

        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "usermount",
                       SYSCTL_DESCR("Whether unprivileged users may mount "
                                    "filesystems"),
                       sysctl_extensions_user_handler, 0, &dovfsusermount, 0,
                       CTL_VFS, VFS_GENERIC, VFS_USERMOUNT, CTL_EOL);
}

static int
secmodel_extensions_system_cb(kauth_cred_t cred, kauth_action_t action,
    void *cookie, void *arg0, void *arg1, void *arg2, void *arg3)
{
        vnode_t *vp;
        struct vattr va;
        struct mount *mp;
        u_long flags;
        int result;
        enum kauth_system_req req;
        int error;

        req = (enum kauth_system_req)(uintptr_t)arg0;
        result = KAUTH_RESULT_DEFER;

        switch (action) {
        case KAUTH_SYSTEM_MOUNT:
                if (dovfsusermount == 0)
                        break;
                switch (req) {
                case KAUTH_REQ_SYSTEM_MOUNT_NEW:
                        vp = (vnode_t *)arg1;
                        mp = vp->v_mount;
                        flags = (u_long)arg2;

                        /*
                         * Ensure that the user owns the directory onto which
                         * the mount is attempted.
                         */
                        vn_lock(vp, LK_SHARED | LK_RETRY);
                        error = VOP_GETATTR(vp, &va, cred);
                        VOP_UNLOCK(vp);
                        if (error)
                                break;

                        if (va.va_uid != kauth_cred_geteuid(cred))
                                break;

                        error = usermount_common_policy(mp, flags);
                        if (error)
                                break;

                        result = KAUTH_RESULT_ALLOW;

                        break;

                case KAUTH_REQ_SYSTEM_MOUNT_UNMOUNT:
                        mp = arg1;

                        /* Must own the mount. */
                        if (mp->mnt_stat.f_owner == kauth_cred_geteuid(cred))
                                result = KAUTH_RESULT_ALLOW;

                        break;

                case KAUTH_REQ_SYSTEM_MOUNT_UPDATE:
                        mp = arg1;
                        flags = (u_long)arg2;

                        /* Must own the mount. */
                        if (mp->mnt_stat.f_owner == kauth_cred_geteuid(cred) &&
                                usermount_common_policy(mp, flags) == 0)
                                result = KAUTH_RESULT_ALLOW;

                        break;

                default:
                        break;
                }
                break;

        default:
                break;
        }

        return (result);
}

static int
secmodel_extensions_vnode_cb(kauth_cred_t cred, kauth_action_t action,
    void *cookie, void *arg0, void *arg1, void *arg2, void *arg3)
{
        int error;
        bool isroot;
        struct vattr va;

        if ((action & KAUTH_VNODE_ADD_LINK) == 0)
                return KAUTH_RESULT_DEFER;

        error = VOP_GETATTR((vnode_t *)arg0, &va, cred);
        if (error)
                goto checkroot;

        if (hardlink_check_uid && kauth_cred_geteuid(cred) != va.va_uid)
                goto checkroot;

        if (hardlink_check_gid && kauth_cred_groupmember(cred, va.va_gid) != 0)
                goto checkroot;

        return KAUTH_RESULT_DEFER;
checkroot:
        error = secmodel_eval("org.netbsd.secmodel.suser", "is-root",
            cred, &isroot);
        if (error || !isroot)
                return KAUTH_RESULT_DENY;

        return KAUTH_RESULT_DEFER;
}