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39705a6c29
When a process' cred struct is replaced, this _almost_ always invokes
the cred_prepare LSM hook; but in one special case (when
KEYCTL_SESSION_TO_PARENT updates the parent's credentials), the
cred_transfer LSM hook is used instead. Landlock only implements the
cred_prepare hook, not cred_transfer, so KEYCTL_SESSION_TO_PARENT causes
all information on Landlock restrictions to be lost.
This basically means that a process with the ability to use the fork()
and keyctl() syscalls can get rid of all Landlock restrictions on
itself.
Fix it by adding a cred_transfer hook that does the same thing as the
existing cred_prepare hook. (Implemented by having hook_cred_prepare()
call hook_cred_transfer() so that the two functions are less likely to
accidentally diverge in the future.)
Cc: stable@kernel.org
Fixes: 385975dca5 ("landlock: Set up the security framework and manage credentials")
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/r/20240724-landlock-houdini-fix-v1-1-df89a4560ca3@google.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
54 lines
1.2 KiB
C
54 lines
1.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Landlock LSM - Credential hooks
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*
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* Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
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* Copyright © 2018-2020 ANSSI
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*/
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#include <linux/cred.h>
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#include <linux/lsm_hooks.h>
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#include "common.h"
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#include "cred.h"
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#include "ruleset.h"
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#include "setup.h"
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static void hook_cred_transfer(struct cred *const new,
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const struct cred *const old)
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{
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struct landlock_ruleset *const old_dom = landlock_cred(old)->domain;
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if (old_dom) {
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landlock_get_ruleset(old_dom);
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landlock_cred(new)->domain = old_dom;
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}
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}
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static int hook_cred_prepare(struct cred *const new,
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const struct cred *const old, const gfp_t gfp)
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{
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hook_cred_transfer(new, old);
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return 0;
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}
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static void hook_cred_free(struct cred *const cred)
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{
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struct landlock_ruleset *const dom = landlock_cred(cred)->domain;
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if (dom)
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landlock_put_ruleset_deferred(dom);
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}
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static struct security_hook_list landlock_hooks[] __ro_after_init = {
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LSM_HOOK_INIT(cred_prepare, hook_cred_prepare),
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LSM_HOOK_INIT(cred_transfer, hook_cred_transfer),
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LSM_HOOK_INIT(cred_free, hook_cred_free),
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};
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__init void landlock_add_cred_hooks(void)
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{
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security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
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&landlock_lsmid);
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}
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