/* $NetBSD: secmodel_extensions.c,v 1.16 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.c,v 1.16 2023/04/22 13:54:19 riastradh Exp $");

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

#include <sys/mount.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <sys/proc.h>
#include <sys/ptrace.h>
#include <sys/module.h>

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

MODULE(MODULE_CLASS_SECMODEL, extensions, NULL);

static int curtain;
static int user_set_cpu_affinity;

#ifdef PT_SETDBREGS
int user_set_dbregs;
#endif

static kauth_listener_t l_process, l_network;

static secmodel_t extensions_sm;

static void secmodel_extensions_init(void);
static void secmodel_extensions_start(void);
static void secmodel_extensions_stop(void);

static void sysctl_security_extensions_setup(struct sysctllog **);
static int  sysctl_extensions_curtain_handler(SYSCTLFN_PROTO);
static bool is_securelevel_above(int);

static int secmodel_extensions_process_cb(kauth_cred_t, kauth_action_t,
    void *, void *, void *, void *, void *);
static int secmodel_extensions_network_cb(kauth_cred_t, kauth_action_t,
    void *, void *, void *, void *, void *);

SYSCTL_SETUP(sysctl_security_extensions_setup,
    "security extensions sysctl")
{
        const struct sysctlnode *rnode, *rnode2;

        sysctl_createv(clog, 0, NULL, &rnode,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_NODE, "models", NULL,
                       NULL, 0, NULL, 0,
                       CTL_SECURITY, CTL_CREATE, CTL_EOL);

        /* Compatibility: security.models.bsd44 */
        rnode2 = rnode;
        sysctl_createv(clog, 0, &rnode2, &rnode2,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_NODE, "bsd44", NULL,
                       NULL, 0, NULL, 0,
                       CTL_CREATE, CTL_EOL);

        /* Compatibility: security.models.bsd44.curtain */
        sysctl_createv(clog, 0, &rnode2, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "curtain",
                       SYSCTL_DESCR("Curtain information about objects to "\
                                    "users not owning them."),
                       sysctl_extensions_curtain_handler, 0, &curtain, 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(clog, 0, &rnode, &rnode,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_NODE, "extensions", NULL,
                       NULL, 0, NULL, 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_STRING, "name", NULL,
                       NULL, 0, __UNCONST(SECMODEL_EXTENSIONS_NAME), 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "curtain",
                       SYSCTL_DESCR("Curtain information about objects to "\
                                    "users not owning them."),
                       sysctl_extensions_curtain_handler, 0, &curtain, 0,
                       CTL_CREATE, CTL_EOL);

        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "user_set_cpu_affinity",
                       SYSCTL_DESCR("Whether unprivileged users may control "\
                                    "CPU affinity."),
                       sysctl_extensions_user_handler, 0,
                       &user_set_cpu_affinity, 0,
                       CTL_CREATE, CTL_EOL);

#ifdef PT_SETDBREGS
        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "user_set_dbregs",
                       SYSCTL_DESCR("Whether unprivileged users may set "\
                                    "CPU Debug Registers."),
                       sysctl_extensions_user_handler, 0,
                       &user_set_dbregs, 0,
                       CTL_CREATE, CTL_EOL);
#endif

        /* Compatibility: security.curtain */
        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "curtain",
                       SYSCTL_DESCR("Curtain information about objects to "\
                                    "users not owning them."),
                       sysctl_extensions_curtain_handler, 0, &curtain, 0,
                       CTL_SECURITY, CTL_CREATE, CTL_EOL);

        secmodel_extensions_vfs_sysctl(clog, rnode);
}

static int
sysctl_extensions_curtain_handler(SYSCTLFN_ARGS)
{
        struct sysctlnode node;
        int val, error;

        val = *(int *)rnode->sysctl_data;

        node = *rnode;
        node.sysctl_data = &val;

        error = sysctl_lookup(SYSCTLFN_CALL(&node));
        if (error || newp == NULL)
                return error;

        /* shortcut */
        if (val == *(int *)rnode->sysctl_data)
                return 0;

        /* curtain cannot be disabled when securelevel is above 0 */
        if (val == 0 && is_securelevel_above(0)) {
                return EPERM;
        }

        *(int *)rnode->sysctl_data = val;
        return 0;
}

/*
 * Generic sysctl extensions handler for user mount and set CPU affinity
 * rights. Checks the following conditions:
 * - setting value to 0 is always permitted (decrease user rights)
 * - setting value != 0 is not permitted when securelevel is above 0 (increase
 *   user rights).
 */
int
sysctl_extensions_user_handler(SYSCTLFN_ARGS)
{
        struct sysctlnode node;
        int val, error;

        val = *(int *)rnode->sysctl_data;

        node = *rnode;
        node.sysctl_data = &val;

        error = sysctl_lookup(SYSCTLFN_CALL(&node));
        if (error || newp == NULL)
                return error;

        /* shortcut */
        if (val == *(int *)rnode->sysctl_data)
                return 0;

        /* we cannot grant more rights to users when securelevel is above 0 */
        if (val != 0 && is_securelevel_above(0)) {
                return EPERM;
        }

        *(int *)rnode->sysctl_data = val;
        return 0;
}

/*
 * Query secmodel_securelevel(9) to know whether securelevel is strictly
 * above 'level' or not.
 * Returns true if it is, false otherwise (when securelevel is absent or
 * securelevel is at or below 'level').
 */
static bool
is_securelevel_above(int level)
{
        bool above;
        int error;

        error = secmodel_eval("org.netbsd.secmodel.securelevel",
            "is-securelevel-above", KAUTH_ARG(level), &above);
        if (error == 0 && above)
                return true;
        else
                return false;
}

static void
secmodel_extensions_init(void)
{

        curtain = 0;
        user_set_cpu_affinity = 0;
#ifdef PT_SETDBREGS
        user_set_dbregs = 0;
#endif
}

static void
secmodel_extensions_start(void)
{

        l_process = kauth_listen_scope(KAUTH_SCOPE_PROCESS,
            secmodel_extensions_process_cb, NULL);
        l_network = kauth_listen_scope(KAUTH_SCOPE_NETWORK,
            secmodel_extensions_network_cb, NULL);
        secmodel_extensions_vfs_start();
}

static void
secmodel_extensions_stop(void)
{

        secmodel_extensions_vfs_stop();
        kauth_unlisten_scope(l_process);
        kauth_unlisten_scope(l_network);
}

static int
extensions_modcmd(modcmd_t cmd, void *arg)
{
        int error = 0;

        switch (cmd) {
        case MODULE_CMD_INIT:
                error = secmodel_register(&extensions_sm,
                    SECMODEL_EXTENSIONS_ID, SECMODEL_EXTENSIONS_NAME,
                    NULL, NULL, NULL);
                if (error != 0)
                        printf("extensions_modcmd::init: secmodel_register "
                            "returned %d\n", error);

                secmodel_extensions_init();
                secmodel_extensions_start();
                break;

        case MODULE_CMD_FINI:
                secmodel_extensions_stop();

                error = secmodel_deregister(extensions_sm);
                if (error != 0)
                        printf("extensions_modcmd::fini: secmodel_deregister "
                            "returned %d\n", error);

                break;

        case MODULE_CMD_AUTOUNLOAD:
                error = EPERM;
                break;

        default:
                error = ENOTTY;
                break;
        }

        return (error);
}

static int
secmodel_extensions_process_cb(kauth_cred_t cred, kauth_action_t action,
    void *cookie, void *arg0, void *arg1, void *arg2, void *arg3)
{
        int result;
        enum kauth_process_req req;

        result = KAUTH_RESULT_DEFER;
        req = (enum kauth_process_req)(uintptr_t)arg1;

        switch (action) {
        case KAUTH_PROCESS_CANSEE:
                switch (req) {
                case KAUTH_REQ_PROCESS_CANSEE_ARGS:
                case KAUTH_REQ_PROCESS_CANSEE_ENTRY:
                case KAUTH_REQ_PROCESS_CANSEE_OPENFILES:
                case KAUTH_REQ_PROCESS_CANSEE_EPROC:
                        if (curtain != 0) {
                                struct proc *p = arg0;

                                /*
                                 * Only process' owner and root can see
                                 * through curtain
                                 */
                                if (!kauth_cred_uidmatch(cred, p->p_cred)) {
                                        int error;
                                        bool isroot = false;

                                        error = secmodel_eval(
                                            "org.netbsd.secmodel.suser",
                                            "is-root", cred, &isroot);
                                        if (error == 0 && !isroot)
                                                result = KAUTH_RESULT_DENY;
                                }
                        }

                        break;

                case KAUTH_REQ_PROCESS_CANSEE_KPTR:
                default:
                        break;
                }

                break;

        case KAUTH_PROCESS_SCHEDULER_SETAFFINITY:
                if (user_set_cpu_affinity != 0) {
                        struct proc *p = arg0;

                        if (kauth_cred_uidmatch(cred, p->p_cred))
                                result = KAUTH_RESULT_ALLOW;
                }
                break;

        default:
                break;
        }

        return (result);
}

static int
secmodel_extensions_network_cb(kauth_cred_t cred, kauth_action_t action,
    void *cookie, void *arg0, void *arg1, void *arg2, void *arg3)
{
        int result;
        enum kauth_network_req req;

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

        if (action != KAUTH_NETWORK_SOCKET ||
            req != KAUTH_REQ_NETWORK_SOCKET_CANSEE)
                return result;

        if (curtain != 0) {
                struct socket *so = (struct socket *)arg1;

                if (__predict_false(so == NULL || so->so_cred == NULL))
                        return KAUTH_RESULT_DENY;

                if (!kauth_cred_uidmatch(cred, so->so_cred)) {
                        int error;
                        bool isroot = false;

                        error = secmodel_eval("org.netbsd.secmodel.suser",
                            "is-root", cred, &isroot);
                        if (error == 0 && !isroot)
                                result = KAUTH_RESULT_DENY;
                }
        }

        return (result);
}