2019-01-16 23:46:06 +08:00
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// SPDX-License-Identifier: GPL-2.0
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/*
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* SafeSetID Linux Security Module
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*
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* Author: Micah Morton <mortonm@chromium.org>
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*
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* Copyright (C) 2018 The Chromium OS Authors.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2, as
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* published by the Free Software Foundation.
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*
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*/
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#define pr_fmt(fmt) "SafeSetID: " fmt
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#include <linux/lsm_hooks.h>
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#include <linux/module.h>
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#include <linux/ptrace.h>
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#include <linux/sched/task_stack.h>
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#include <linux/security.h>
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2019-04-11 00:55:34 +08:00
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#include "lsm.h"
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2019-01-16 23:46:06 +08:00
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/* Flag indicating whether initialization completed */
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int safesetid_initialized;
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2019-04-11 00:55:34 +08:00
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#define NUM_BITS 8 /* 256 buckets in hash table */
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2019-01-16 23:46:06 +08:00
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static DEFINE_HASHTABLE(safesetid_whitelist_hashtable, NUM_BITS);
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static DEFINE_SPINLOCK(safesetid_whitelist_hashtable_spinlock);
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2019-04-11 00:55:34 +08:00
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static enum sid_policy_type setuid_policy_lookup(kuid_t src, kuid_t dst)
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{
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struct entry *entry;
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enum sid_policy_type result = SIDPOL_DEFAULT;
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2019-01-16 23:46:06 +08:00
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rcu_read_lock();
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hash_for_each_possible_rcu(safesetid_whitelist_hashtable,
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2019-04-11 00:55:34 +08:00
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entry, next, __kuid_val(src)) {
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if (!uid_eq(entry->src_uid, src))
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continue;
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if (uid_eq(entry->dst_uid, dst)) {
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2019-01-16 23:46:06 +08:00
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rcu_read_unlock();
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2019-04-11 00:55:34 +08:00
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return SIDPOL_ALLOWED;
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}
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result = SIDPOL_CONSTRAINED;
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}
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rcu_read_unlock();
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2019-04-11 00:55:34 +08:00
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return result;
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2019-01-16 23:46:06 +08:00
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}
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static int safesetid_security_capable(const struct cred *cred,
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struct user_namespace *ns,
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int cap,
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unsigned int opts)
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{
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if (cap == CAP_SETUID &&
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setuid_policy_lookup(cred->uid, INVALID_UID) != SIDPOL_DEFAULT) {
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if (!(opts & CAP_OPT_INSETID)) {
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/*
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* Deny if we're not in a set*uid() syscall to avoid
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* giving powers gated by CAP_SETUID that are related
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* to functionality other than calling set*uid() (e.g.
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* allowing user to set up userns uid mappings).
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*/
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2019-04-11 00:54:34 +08:00
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pr_warn("Operation requires CAP_SETUID, which is not available to UID %u for operations besides approved set*uid transitions\n",
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__kuid_val(cred->uid));
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return -1;
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}
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}
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return 0;
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}
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LSM: SafeSetID: fix check for setresuid(new1, new2, new3)
With the old code, when a process with the (real,effective,saved) UID set
(1,1,1) calls setresuid(2,3,4), safesetid_task_fix_setuid() only checks
whether the transition 1->2 is permitted; the transitions 1->3 and 1->4 are
not checked. Fix this.
This is also a good opportunity to refactor safesetid_task_fix_setuid() to
be less verbose - having one branch per set*uid() syscall is unnecessary.
Note that this slightly changes semantics: The UID transition check for
UIDs that were not in the old cred struct is now always performed against
the policy of the RUID. I think that's more consistent anyway, since the
RUID is also the one that decides whether any policy is enforced at all.
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>
2019-04-11 00:55:19 +08:00
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/*
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* Check whether a caller with old credentials @old is allowed to switch to
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* credentials that contain @new_uid.
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*/
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static bool uid_permitted_for_cred(const struct cred *old, kuid_t new_uid)
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{
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LSM: SafeSetID: fix check for setresuid(new1, new2, new3)
With the old code, when a process with the (real,effective,saved) UID set
(1,1,1) calls setresuid(2,3,4), safesetid_task_fix_setuid() only checks
whether the transition 1->2 is permitted; the transitions 1->3 and 1->4 are
not checked. Fix this.
This is also a good opportunity to refactor safesetid_task_fix_setuid() to
be less verbose - having one branch per set*uid() syscall is unnecessary.
Note that this slightly changes semantics: The UID transition check for
UIDs that were not in the old cred struct is now always performed against
the policy of the RUID. I think that's more consistent anyway, since the
RUID is also the one that decides whether any policy is enforced at all.
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>
2019-04-11 00:55:19 +08:00
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bool permitted;
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/* If our old creds already had this UID in it, it's fine. */
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if (uid_eq(new_uid, old->uid) || uid_eq(new_uid, old->euid) ||
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uid_eq(new_uid, old->suid))
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return true;
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2019-01-16 23:46:06 +08:00
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/*
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LSM: SafeSetID: fix check for setresuid(new1, new2, new3)
With the old code, when a process with the (real,effective,saved) UID set
(1,1,1) calls setresuid(2,3,4), safesetid_task_fix_setuid() only checks
whether the transition 1->2 is permitted; the transitions 1->3 and 1->4 are
not checked. Fix this.
This is also a good opportunity to refactor safesetid_task_fix_setuid() to
be less verbose - having one branch per set*uid() syscall is unnecessary.
Note that this slightly changes semantics: The UID transition check for
UIDs that were not in the old cred struct is now always performed against
the policy of the RUID. I think that's more consistent anyway, since the
RUID is also the one that decides whether any policy is enforced at all.
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>
2019-04-11 00:55:19 +08:00
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* Transitions to new UIDs require a check against the policy of the old
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* RUID.
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*/
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permitted =
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setuid_policy_lookup(old->uid, new_uid) != SIDPOL_CONSTRAINED;
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LSM: SafeSetID: fix check for setresuid(new1, new2, new3)
With the old code, when a process with the (real,effective,saved) UID set
(1,1,1) calls setresuid(2,3,4), safesetid_task_fix_setuid() only checks
whether the transition 1->2 is permitted; the transitions 1->3 and 1->4 are
not checked. Fix this.
This is also a good opportunity to refactor safesetid_task_fix_setuid() to
be less verbose - having one branch per set*uid() syscall is unnecessary.
Note that this slightly changes semantics: The UID transition check for
UIDs that were not in the old cred struct is now always performed against
the policy of the RUID. I think that's more consistent anyway, since the
RUID is also the one that decides whether any policy is enforced at all.
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>
2019-04-11 00:55:19 +08:00
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if (!permitted) {
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pr_warn("UID transition ((%d,%d,%d) -> %d) blocked\n",
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__kuid_val(old->uid), __kuid_val(old->euid),
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__kuid_val(old->suid), __kuid_val(new_uid));
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}
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return permitted;
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}
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/*
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* Check whether there is either an exception for user under old cred struct to
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* set*uid to user under new cred struct, or the UID transition is allowed (by
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* Linux set*uid rules) even without CAP_SETUID.
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*/
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static int safesetid_task_fix_setuid(struct cred *new,
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const struct cred *old,
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int flags)
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{
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LSM: SafeSetID: fix check for setresuid(new1, new2, new3)
With the old code, when a process with the (real,effective,saved) UID set
(1,1,1) calls setresuid(2,3,4), safesetid_task_fix_setuid() only checks
whether the transition 1->2 is permitted; the transitions 1->3 and 1->4 are
not checked. Fix this.
This is also a good opportunity to refactor safesetid_task_fix_setuid() to
be less verbose - having one branch per set*uid() syscall is unnecessary.
Note that this slightly changes semantics: The UID transition check for
UIDs that were not in the old cred struct is now always performed against
the policy of the RUID. I think that's more consistent anyway, since the
RUID is also the one that decides whether any policy is enforced at all.
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>
2019-04-11 00:55:19 +08:00
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/* Do nothing if there are no setuid restrictions for our old RUID. */
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2019-04-11 00:55:34 +08:00
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if (setuid_policy_lookup(old->uid, INVALID_UID) == SIDPOL_DEFAULT)
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return 0;
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LSM: SafeSetID: fix check for setresuid(new1, new2, new3)
With the old code, when a process with the (real,effective,saved) UID set
(1,1,1) calls setresuid(2,3,4), safesetid_task_fix_setuid() only checks
whether the transition 1->2 is permitted; the transitions 1->3 and 1->4 are
not checked. Fix this.
This is also a good opportunity to refactor safesetid_task_fix_setuid() to
be less verbose - having one branch per set*uid() syscall is unnecessary.
Note that this slightly changes semantics: The UID transition check for
UIDs that were not in the old cred struct is now always performed against
the policy of the RUID. I think that's more consistent anyway, since the
RUID is also the one that decides whether any policy is enforced at all.
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>
2019-04-11 00:55:19 +08:00
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if (uid_permitted_for_cred(old, new->uid) &&
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uid_permitted_for_cred(old, new->euid) &&
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uid_permitted_for_cred(old, new->suid) &&
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uid_permitted_for_cred(old, new->fsuid))
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return 0;
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/*
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* Kill this process to avoid potential security vulnerabilities
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* that could arise from a missing whitelist entry preventing a
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* privileged process from dropping to a lesser-privileged one.
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*/
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force_sig(SIGKILL);
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return -EACCES;
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2019-01-16 23:46:06 +08:00
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}
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int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child)
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{
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struct entry *new;
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/* Return if entry already exists */
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if (setuid_policy_lookup(parent, child) == SIDPOL_ALLOWED)
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return 0;
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new = kzalloc(sizeof(struct entry), GFP_KERNEL);
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if (!new)
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return -ENOMEM;
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new->src_uid = parent;
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new->dst_uid = child;
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2019-01-16 23:46:06 +08:00
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spin_lock(&safesetid_whitelist_hashtable_spinlock);
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hash_add_rcu(safesetid_whitelist_hashtable,
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&new->next,
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__kuid_val(parent));
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spin_unlock(&safesetid_whitelist_hashtable_spinlock);
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return 0;
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}
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void flush_safesetid_whitelist_entries(void)
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{
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struct entry *entry;
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struct hlist_node *hlist_node;
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unsigned int bkt_loop_cursor;
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HLIST_HEAD(free_list);
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/*
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* Could probably use hash_for_each_rcu here instead, but this should
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* be fine as well.
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*/
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spin_lock(&safesetid_whitelist_hashtable_spinlock);
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hash_for_each_safe(safesetid_whitelist_hashtable, bkt_loop_cursor,
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hlist_node, entry, next) {
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hash_del_rcu(&entry->next);
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hlist_add_head(&entry->dlist, &free_list);
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}
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spin_unlock(&safesetid_whitelist_hashtable_spinlock);
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synchronize_rcu();
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hlist_for_each_entry_safe(entry, hlist_node, &free_list, dlist) {
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hlist_del(&entry->dlist);
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kfree(entry);
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}
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}
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static struct security_hook_list safesetid_security_hooks[] = {
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LSM_HOOK_INIT(task_fix_setuid, safesetid_task_fix_setuid),
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LSM_HOOK_INIT(capable, safesetid_security_capable)
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};
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static int __init safesetid_security_init(void)
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{
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security_add_hooks(safesetid_security_hooks,
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ARRAY_SIZE(safesetid_security_hooks), "safesetid");
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/* Report that SafeSetID successfully initialized */
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safesetid_initialized = 1;
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return 0;
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}
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DEFINE_LSM(safesetid_security_init) = {
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.init = safesetid_security_init,
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.name = "safesetid",
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};
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