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cab1056105
Currently, sysctls which enable KDB in some way are flagged with
CTLFLAG_SECURE, meaning that you can't modify them if securelevel > 0.
This is so that KDB cannot be used to lower a running system's
securelevel, see commit 3d7618d8bf. However, the newer mac_ddb(4)
restricts DDB operations which could be abused to lower securelevel
while retaining some ability to gather useful debugging information.
To enable the use of KDB (specifically, DDB) on systems with a raised
securelevel, change the KDB sysctl policy: rather than relying on
CTLFLAG_SECURE, add a check of the current securelevel to kdb_trap().
If the securelevel is raised, only pass control to the backend if MAC
specifically grants access; otherwise simply check to see if mac_ddb
vetoes the request, as before.
Add a new secure sysctl, debug.kdb.enter_securelevel, to override this
behaviour. That is, the sysctl lets one enter a KDB backend even with a
raised securelevel, so long as it is set before the securelevel is
raised.
Reviewed by: mhorne, stevek
MFC after: 1 month
Sponsored by: Juniper Networks
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D37122
79 lines
2.4 KiB
C
79 lines
2.4 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause
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*
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* Copyright (c) 2021-2022 Klara Systems
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*
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* This software was developed by Mitchell Horne <mhorne@FreeBSD.org>
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* under sponsorship from Juniper Networks and Klara Systems.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "opt_mac.h"
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/module.h>
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#include <ddb/ddb.h>
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#include <security/mac/mac_framework.h>
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#include <security/mac/mac_internal.h>
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#include <security/mac/mac_policy.h>
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int
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mac_kdb_grant_backend(struct kdb_dbbe *be)
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{
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int error = 0;
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MAC_POLICY_GRANT_NOSLEEP(kdb_check_backend, be);
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return (error);
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}
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int
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mac_kdb_check_backend(struct kdb_dbbe *be)
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{
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int error = 0;
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MAC_POLICY_CHECK_NOSLEEP(kdb_check_backend, be);
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return (error);
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}
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int
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mac_ddb_command_register(struct db_command_table *table, struct db_command *cmd)
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{
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int error = 0;
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MAC_POLICY_CHECK_NOSLEEP(ddb_command_register, table, cmd);
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return (error);
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}
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int
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mac_ddb_command_exec(struct db_command *cmd, db_expr_t addr,
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bool have_addr, db_expr_t count, char *modif)
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{
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int error = 0;
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MAC_POLICY_CHECK_NOSLEEP(ddb_command_exec, cmd, addr, have_addr,
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count, modif);
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return (error);
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}
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