cred.c

/* Task credentials management - see Documentation/security/credentials.txt
 *
 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */
#include <linux/export.h>
#include <linux/cred.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/key.h>
#include <linux/keyctl.h>
#include <linux/init_task.h>
#include <linux/security.h>
#include <linux/binfmts.h>
#include <linux/cn_proc.h>

#if 0
#define kdebug(FMT, ...) \
	printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
#else
#define kdebug(FMT, ...) \
	no_printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
#endif

// ARM10C 20150919
// ARM10C 20160910
static struct kmem_cache *cred_jar;

/*
 * The initial credentials for the initial task
 */
// ARM10C 20160319
// ARM10C 20160903
// ARM10C 20160910
// INIT_USER: (&root_user)
// CAP_FULL_SET: ((kernel_cap_t){{ 0xFFFFFFFF, 0xFFFFFFFF }})
struct cred init_cred = {
	.usage			= ATOMIC_INIT(4),
#ifdef CONFIG_DEBUG_CREDENTIALS
	.subscribers		= ATOMIC_INIT(2),
	.magic			= CRED_MAGIC,
#endif
	.uid			= GLOBAL_ROOT_UID,
	.gid			= GLOBAL_ROOT_GID,
	.suid			= GLOBAL_ROOT_UID,
	.sgid			= GLOBAL_ROOT_GID,
	.euid			= GLOBAL_ROOT_UID,
	.egid			= GLOBAL_ROOT_GID,
	// GLOBAL_ROOT_UID: 0
	.fsuid			= GLOBAL_ROOT_UID,
	// GLOBAL_ROOT_GID: 0
	.fsgid			= GLOBAL_ROOT_GID,
	.securebits		= SECUREBITS_DEFAULT,
	.cap_inheritable	= CAP_EMPTY_SET,
	.cap_permitted		= CAP_FULL_SET,
	.cap_effective		= CAP_FULL_SET,
	.cap_bset		= CAP_FULL_SET,
	.user			= INIT_USER,
	.user_ns		= &init_user_ns,
	.group_info		= &init_groups,
};

// ARM10C 20160910
// new: kmem_cache#16-oX (struct cred), 0
static inline void set_cred_subscribers(struct cred *cred, int n)
{
#ifdef CONFIG_DEBUG_CREDENTIALS // CONFIG_DEBUG_CREDENTIALS=n
	atomic_set(&cred->subscribers, n);
#endif
}

static inline int read_cred_subscribers(const struct cred *cred)
{
#ifdef CONFIG_DEBUG_CREDENTIALS
	return atomic_read(&cred->subscribers);
#else
	return 0;
#endif
}

// ARM10C 20160910
// new: kmem_cache#16-oX (struct cred), 2
// ARM10C 20170524
// new: kmem_cache#16-oX (struct cred)
static inline void alter_cred_subscribers(const struct cred *_cred, int n)
{
#ifdef CONFIG_DEBUG_CREDENTIALS // CONFIG_DEBUG_CREDENTIALS=n
	struct cred *cred = (struct cred *) _cred;

	atomic_add(n, &cred->subscribers);
#endif
}

/*
 * The RCU callback to actually dispose of a set of credentials
 */
static void put_cred_rcu(struct rcu_head *rcu)
{
	struct cred *cred = container_of(rcu, struct cred, rcu);

	kdebug("put_cred_rcu(%p)", cred);

#ifdef CONFIG_DEBUG_CREDENTIALS
	if (cred->magic != CRED_MAGIC_DEAD ||
	    atomic_read(&cred->usage) != 0 ||
	    read_cred_subscribers(cred) != 0)
		panic("CRED: put_cred_rcu() sees %p with"
		      " mag %x, put %p, usage %d, subscr %d\n",
		      cred, cred->magic, cred->put_addr,
		      atomic_read(&cred->usage),
		      read_cred_subscribers(cred));
#else
	if (atomic_read(&cred->usage) != 0)
		panic("CRED: put_cred_rcu() sees %p with usage %d\n",
		      cred, atomic_read(&cred->usage));
#endif

	security_cred_free(cred);
	key_put(cred->session_keyring);
	key_put(cred->process_keyring);
	key_put(cred->thread_keyring);
	key_put(cred->request_key_auth);
	if (cred->group_info)
		put_group_info(cred->group_info);
	free_uid(cred->user);
	put_user_ns(cred->user_ns);
	kmem_cache_free(cred_jar, cred);
}

/**
 * __put_cred - Destroy a set of credentials
 * @cred: The record to release
 *
 * Destroy a set of credentials on which no references remain.
 */
void __put_cred(struct cred *cred)
{
	kdebug("__put_cred(%p{%d,%d})", cred,
	       atomic_read(&cred->usage),
	       read_cred_subscribers(cred));

	BUG_ON(atomic_read(&cred->usage) != 0);
#ifdef CONFIG_DEBUG_CREDENTIALS
	BUG_ON(read_cred_subscribers(cred) != 0);
	cred->magic = CRED_MAGIC_DEAD;
	cred->put_addr = __builtin_return_address(0);
#endif
	BUG_ON(cred == current->cred);
	BUG_ON(cred == current->real_cred);

	call_rcu(&cred->rcu, put_cred_rcu);
}
EXPORT_SYMBOL(__put_cred);

/*
 * Clean up a task's credentials when it exits
 */
void exit_creds(struct task_struct *tsk)
{
	struct cred *cred;

	kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
	       atomic_read(&tsk->cred->usage),
	       read_cred_subscribers(tsk->cred));

	cred = (struct cred *) tsk->real_cred;
	tsk->real_cred = NULL;
	validate_creds(cred);
	alter_cred_subscribers(cred, -1);
	put_cred(cred);

	cred = (struct cred *) tsk->cred;
	tsk->cred = NULL;
	validate_creds(cred);
	alter_cred_subscribers(cred, -1);
	put_cred(cred);
}

/**
 * get_task_cred - Get another task's objective credentials
 * @task: The task to query
 *
 * Get the objective credentials of a task, pinning them so that they can't go
 * away.  Accessing a task's credentials directly is not permitted.
 *
 * The caller must also make sure task doesn't get deleted, either by holding a
 * ref on task or by holding tasklist_lock to prevent it from being unlinked.
 */
const struct cred *get_task_cred(struct task_struct *task)
{
	const struct cred *cred;

	rcu_read_lock();

	do {
		cred = __task_cred((task));
		BUG_ON(!cred);
	} while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));

	rcu_read_unlock();
	return cred;
}

/*
 * Allocate blank credentials, such that the credentials can be filled in at a
 * later date without risk of ENOMEM.
 */
struct cred *cred_alloc_blank(void)
{
	struct cred *new;

	new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
	if (!new)
		return NULL;

	atomic_set(&new->usage, 1);
#ifdef CONFIG_DEBUG_CREDENTIALS
	new->magic = CRED_MAGIC;
#endif

	if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
		goto error;

	return new;

error:
	abort_creds(new);
	return NULL;
}

/**
 * prepare_creds - Prepare a new set of credentials for modification
 *
 * Prepare a new set of task credentials for modification.  A task's creds
 * shouldn't generally be modified directly, therefore this function is used to
 * prepare a new copy, which the caller then modifies and then commits by
 * calling commit_creds().
 *
 * Preparation involves making a copy of the objective creds for modification.
 *
 * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
 *
 * Call commit_creds() or abort_creds() to clean up.
 */
// ARM10C 20160910
// ARM10C 20170524
struct cred *prepare_creds(void)
{
	// current: &init_task
	// current: &init_task
	struct task_struct *task = current;
	// task: &init_task
	// task: &init_task

	const struct cred *old;
	struct cred *new;

	validate_process_creds(); // null function

	// cred_jar: kmem_cache#16, GFP_KERNEL: 0xD0
	// kmem_cache_alloc(kmem_cache#16, GFP_KERNEL: 0xD0): kmem_cache#16-oX (struct cred)
	// cred_jar: kmem_cache#16, GFP_KERNEL: 0xD0
	// kmem_cache_alloc(kmem_cache#16, GFP_KERNEL: 0xD0): kmem_cache#16-oX (struct cred)
	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)

	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)
	if (!new)
		return NULL;

	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)
	kdebug("prepare_creds() alloc %p", new);
	// "prepare_creds() alloc 0xXXXXXXXX"
	// "prepare_creds() alloc 0xXXXXXXXX"

	// task->cred: (&init_task)->cred: &init_cred
	// task->cred: (&init_task)->cred: &init_cred
	old = task->cred;
	// old: &init_cred
	// old: &init_cred

	// new: kmem_cache#16-oX (struct cred), old: &init_cred, sizeof(struct cred): 92 bytes
	// new: kmem_cache#16-oX (struct cred), old: &init_cred, sizeof(struct cred): 92 bytes
	memcpy(new, old, sizeof(struct cred));

	// memcpy 에서 한일:
	// kmem_cache#16-oX (struct cred) 에 init_cred 에 있는 맴버값 전부를 복사함

	// memcpy 에서 한일:
	// kmem_cache#16-oX (struct cred) 에 init_cred 에 있는 맴버값 전부를 복사함

	// &new->usage: &(kmem_cache#16-oX (struct cred))->usage
	// &new->usage: &(kmem_cache#16-oX (struct cred))->usage
	atomic_set(&new->usage, 1);

	// atomic_set 에서 한일:
	// (&(kmem_cache#16-oX (struct cred))->usage)->counter: 1

	// atomic_set 에서 한일:
	// (&(kmem_cache#16-oX (struct cred))->usage)->counter: 1

	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)
	set_cred_subscribers(new, 0); // null function

	// new->group_info: (kmem_cache#16-oX (struct cred))->group_info: &init_groups
	// get_group_info(&init_groups): &init_groups
	// new->group_info: (kmem_cache#16-oX (struct cred))->group_info: &init_groups
	// get_group_info(&init_groups): &init_groups
	get_group_info(new->group_info);

	// get_group_info 에서 한일:
	// (&(&init_groups)->usage)->counter: 3

	// get_group_info 에서 한일:
	// (&(&init_groups)->usage)->counter: 4

	// new->user: (kmem_cache#16-oX (struct cred))->user: &root_user
	// get_uid(&root_user): &root_user
	// new->user: (kmem_cache#16-oX (struct cred))->user: &root_user
	// get_uid(&root_user): &root_user
	get_uid(new->user);

	// get_uid 에서 한일:
	// (&(&root_user)->__count)->counter: 2

	// get_uid 에서 한일:
	// (&(&root_user)->__count)->counter: 3

	// new->user_ns: (kmem_cache#16-oX (struct cred))->user_ns: &init_user_ns
	// get_user_ns(&init_user_ns): &init_user_ns
	// new->user_ns: (kmem_cache#16-oX (struct cred))->user_ns: &init_user_ns
	// get_user_ns(&init_user_ns): &init_user_ns
	get_user_ns(new->user_ns);

#ifdef CONFIG_KEYS // CONFIG_KEYS=n
	key_get(new->session_keyring);
	key_get(new->process_keyring);
	key_get(new->thread_keyring);
	key_get(new->request_key_auth);
#endif

#ifdef CONFIG_SECURITY // CONFIG_SECURITY=n
	new->security = NULL;
#endif

	// new: kmem_cache#16-oX (struct cred), old: &init_cred, GFP_KERNEL: 0xD0
	// security_prepare_creds(kmem_cache#16-oX (struct cred), &init_cred, 0xD0): 0
	// new: kmem_cache#16-oX (struct cred), old: &init_cred, GFP_KERNEL: 0xD0
	// security_prepare_creds(kmem_cache#16-oX (struct cred), &init_cred, 0xD0): 0
	if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
		goto error;

	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)
	validate_creds(new); // null function

	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)
	return new;
	// return kmem_cache#16-oX (struct cred)
	// return kmem_cache#16-oX (struct cred)

error:
	abort_creds(new);
	return NULL;
}
EXPORT_SYMBOL(prepare_creds);

/*
 * Prepare credentials for current to perform an execve()
 * - The caller must hold ->cred_guard_mutex
 */
struct cred *prepare_exec_creds(void)
{
	struct cred *new;

	new = prepare_creds();
	if (!new)
		return new;

#ifdef CONFIG_KEYS
	/* newly exec'd tasks don't get a thread keyring */
	key_put(new->thread_keyring);
	new->thread_keyring = NULL;

	/* inherit the session keyring; new process keyring */
	key_put(new->process_keyring);
	new->process_keyring = NULL;
#endif

	return new;
}

/*
 * Copy credentials for the new process created by fork()
 *
 * We share if we can, but under some circumstances we have to generate a new
 * set.
 *
 * The new process gets the current process's subjective credentials as its
 * objective and subjective credentials
 */
// ARM10C 20160910
// p: kmem_cache#15-oX (struct task_struct), clone_flags: 0x00800B00
// ARM10C 20170524
// p: kmem_cache#15-oX (struct task_struct), clone_flags: 0x00800700
int copy_creds(struct task_struct *p, unsigned long clone_flags)
{
	struct cred *new;
	int ret;

	// clone_flags: 0x00800B00, CLONE_THREAD: 0x00010000
	// clone_flags: 0x00800700, CLONE_THREAD: 0x00010000
	if (
#ifdef CONFIG_KEYS // CONFIG_KEYS=n
		!p->cred->thread_keyring &&
#endif
		clone_flags & CLONE_THREAD
	    ) {
		p->real_cred = get_cred(p->cred);
		get_cred(p->cred);
		alter_cred_subscribers(p->cred, 2);
		kdebug("share_creds(%p{%d,%d})",
		       p->cred, atomic_read(&p->cred->usage),
		       read_cred_subscribers(p->cred));
		atomic_inc(&p->cred->user->processes);
		return 0;
	}

	// prepare_creds(): kmem_cache#16-oX (struct cred)
	// prepare_creds(): kmem_cache#16-oX (struct cred)
	new = prepare_creds();
	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)

	// prepare_creds 에서 한일:
	// struct cred 만큼의 메모리를 할당 받음
	// kmem_cache#16-oX (struct cred)
	//
	// kmem_cache#16-oX (struct cred) 에 init_cred 에 있는 맴버값 전부를 복사함
	// (&(kmem_cache#16-oX (struct cred))->usage)->counter: 1
	// (&(&init_groups)->usage)->counter: 3
	// (&(&root_user)->__count)->counter: 2

	// prepare_creds 에서 한일:
	// struct cred 만큼의 메모리를 할당 받음
	// kmem_cache#16-oX (struct cred)
	//
	// kmem_cache#16-oX (struct cred) 에 init_cred 에 있는 맴버값 전부를 복사함
	// (&(kmem_cache#16-oX (struct cred))->usage)->counter: 1
	// (&(&init_groups)->usage)->counter: 4
	// (&(&root_user)->__count)->counter: 3

	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)
	if (!new)
		return -ENOMEM;

	// clone_flags: 0x00800B00, CLONE_NEWUSER: 0x10000000
	// clone_flags: 0x00800700, CLONE_NEWUSER: 0x10000000
	if (clone_flags & CLONE_NEWUSER) {
		ret = create_user_ns(new);
		if (ret < 0)
			goto error_put;
	}

#ifdef CONFIG_KEYS // CONFIG_KEYS=n
	/* new threads get their own thread keyrings if their parent already
	 * had one */
	if (new->thread_keyring) {
		key_put(new->thread_keyring);
		new->thread_keyring = NULL;
		if (clone_flags & CLONE_THREAD)
			install_thread_keyring_to_cred(new);
	}

	/* The process keyring is only shared between the threads in a process;
	 * anything outside of those threads doesn't inherit.
	 */
	if (!(clone_flags & CLONE_THREAD)) {
		key_put(new->process_keyring);
		new->process_keyring = NULL;
	}
#endif

	// new: kmem_cache#16-oX (struct cred),
	// new->user: (kmem_cache#16-oX (struct cred))->user: &root_user,
	// &new->user->processes: &(&root_user)->processes
	// new: kmem_cache#16-oX (struct cred),
	// new->user: (kmem_cache#16-oX (struct cred))->user: &root_user,
	// &new->user->processes: &(&root_user)->processes
	atomic_inc(&new->user->processes);

	// atomic_inc 에서 한일:
	// (&(&root_user)->processes)->counter: 2

	// atomic_inc 에서 한일:
	// (&(&root_user)->processes)->counter: 3

	// p->cred: (kmem_cache#15-oX (struct task_struct))->cred,
	// p->real_cred: (kmem_cache#15-oX (struct task_struct))->real_cred,
	// new: kmem_cache#16-oX (struct cred), get_cred(kmem_cache#16-oX (struct cred)): kmem_cache#16-oX (struct cred)
	// p->cred: (kmem_cache#15-oX (struct task_struct))->cred,
	// p->real_cred: (kmem_cache#15-oX (struct task_struct))->real_cred,
	// new: kmem_cache#16-oX (struct cred), get_cred(kmem_cache#16-oX (struct cred)): kmem_cache#16-oX (struct cred)
	p->cred = p->real_cred = get_cred(new);
	// p->cred: (kmem_cache#15-oX (struct task_struct))->cred: kmem_cache#16-oX (struct cred)
	// p->real_cred: (kmem_cache#15-oX (struct task_struct))->real_cred: kmem_cache#16-oX (struct cred)
	// p->cred: (kmem_cache#15-oX (struct task_struct))->cred: kmem_cache#16-oX (struct cred)
	// p->real_cred: (kmem_cache#15-oX (struct task_struct))->real_cred: kmem_cache#16-oX (struct cred)

	// get_cred 에서 한일:
	// (&(kmem_cache#16-oX (struct cred))->usage)->counter: 2

	// get_cred 에서 한일:
	// (&(kmem_cache#16-oX (struct cred))->usage)->counter: 2

	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)
	alter_cred_subscribers(new, 2); // null function

	// new: kmem_cache#16-oX (struct cred)
	// new: kmem_cache#16-oX (struct cred)
	validate_creds(new); // null function

	return 0;
	// return 0
	// return 0

error_put:
	put_cred(new);
	return ret;
}

static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
{
	const struct user_namespace *set_ns = set->user_ns;
	const struct user_namespace *subset_ns = subset->user_ns;

	/* If the two credentials are in the same user namespace see if
	 * the capabilities of subset are a subset of set.
	 */
	if (set_ns == subset_ns)
		return cap_issubset(subset->cap_permitted, set->cap_permitted);

	/* The credentials are in a different user namespaces
	 * therefore one is a subset of the other only if a set is an
	 * ancestor of subset and set->euid is owner of subset or one
	 * of subsets ancestors.
	 */
	for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
		if ((set_ns == subset_ns->parent)  &&
		    uid_eq(subset_ns->owner, set->euid))
			return true;
	}

	return false;
}

/**
 * commit_creds - Install new credentials upon the current task
 * @new: The credentials to be assigned
 *
 * Install a new set of credentials to the current task, using RCU to replace
 * the old set.  Both the objective and the subjective credentials pointers are
 * updated.  This function may not be called if the subjective credentials are
 * in an overridden state.
 *
 * This function eats the caller's reference to the new credentials.
 *
 * Always returns 0 thus allowing this function to be tail-called at the end
 * of, say, sys_setgid().
 */
int commit_creds(struct cred *new)
{
	struct task_struct *task = current;
	const struct cred *old = task->real_cred;

	kdebug("commit_creds(%p{%d,%d})", new,
	       atomic_read(&new->usage),
	       read_cred_subscribers(new));

	BUG_ON(task->cred != old);
#ifdef CONFIG_DEBUG_CREDENTIALS
	BUG_ON(read_cred_subscribers(old) < 2);
	validate_creds(old);
	validate_creds(new);
#endif
	BUG_ON(atomic_read(&new->usage) < 1);

	get_cred(new); /* we will require a ref for the subj creds too */

	/* dumpability changes */
	if (!uid_eq(old->euid, new->euid) ||
	    !gid_eq(old->egid, new->egid) ||
	    !uid_eq(old->fsuid, new->fsuid) ||
	    !gid_eq(old->fsgid, new->fsgid) ||
	    !cred_cap_issubset(old, new)) {
		if (task->mm)
			set_dumpable(task->mm, suid_dumpable);
		task->pdeath_signal = 0;
		smp_wmb();
	}

	/* alter the thread keyring */
	if (!uid_eq(new->fsuid, old->fsuid))
		key_fsuid_changed(task);
	if (!gid_eq(new->fsgid, old->fsgid))
		key_fsgid_changed(task);

	/* do it
	 * RLIMIT_NPROC limits on user->processes have already been checked
	 * in set_user().
	 */
	alter_cred_subscribers(new, 2);
	if (new->user != old->user)
		atomic_inc(&new->user->processes);
	rcu_assign_pointer(task->real_cred, new);
	rcu_assign_pointer(task->cred, new);
	if (new->user != old->user)
		atomic_dec(&old->user->processes);
	alter_cred_subscribers(old, -2);

	/* send notifications */
	if (!uid_eq(new->uid,   old->uid)  ||
	    !uid_eq(new->euid,  old->euid) ||
	    !uid_eq(new->suid,  old->suid) ||
	    !uid_eq(new->fsuid, old->fsuid))
		proc_id_connector(task, PROC_EVENT_UID);

	if (!gid_eq(new->gid,   old->gid)  ||
	    !gid_eq(new->egid,  old->egid) ||
	    !gid_eq(new->sgid,  old->sgid) ||
	    !gid_eq(new->fsgid, old->fsgid))
		proc_id_connector(task, PROC_EVENT_GID);

	/* release the old obj and subj refs both */
	put_cred(old);
	put_cred(old);
	return 0;
}
EXPORT_SYMBOL(commit_creds);

/**
 * abort_creds - Discard a set of credentials and unlock the current task
 * @new: The credentials that were going to be applied
 *
 * Discard a set of credentials that were under construction and unlock the
 * current task.
 */
void abort_creds(struct cred *new)
{
	kdebug("abort_creds(%p{%d,%d})", new,
	       atomic_read(&new->usage),
	       read_cred_subscribers(new));

#ifdef CONFIG_DEBUG_CREDENTIALS
	BUG_ON(read_cred_subscribers(new) != 0);
#endif
	BUG_ON(atomic_read(&new->usage) < 1);
	put_cred(new);
}
EXPORT_SYMBOL(abort_creds);

/**
 * override_creds - Override the current process's subjective credentials
 * @new: The credentials to be assigned
 *
 * Install a set of temporary override subjective credentials on the current
 * process, returning the old set for later reversion.
 */
const struct cred *override_creds(const struct cred *new)
{
	const struct cred *old = current->cred;

	kdebug("override_creds(%p{%d,%d})", new,
	       atomic_read(&new->usage),
	       read_cred_subscribers(new));

	validate_creds(old);
	validate_creds(new);
	get_cred(new);
	alter_cred_subscribers(new, 1);
	rcu_assign_pointer(current->cred, new);
	alter_cred_subscribers(old, -1);

	kdebug("override_creds() = %p{%d,%d}", old,
	       atomic_read(&old->usage),
	       read_cred_subscribers(old));
	return old;
}
EXPORT_SYMBOL(override_creds);

/**
 * revert_creds - Revert a temporary subjective credentials override
 * @old: The credentials to be restored
 *
 * Revert a temporary set of override subjective credentials to an old set,
 * discarding the override set.
 */
void revert_creds(const struct cred *old)
{
	const struct cred *override = current->cred;

	kdebug("revert_creds(%p{%d,%d})", old,
	       atomic_read(&old->usage),
	       read_cred_subscribers(old));

	validate_creds(old);
	validate_creds(override);
	alter_cred_subscribers(old, 1);
	rcu_assign_pointer(current->cred, old);
	alter_cred_subscribers(override, -1);
	put_cred(override);
}
EXPORT_SYMBOL(revert_creds);

/*
 * initialise the credentials stuff
 */
// ARM10C 20150919
void __init cred_init(void)
{
	/* allocate a slab in which we can store credentials */
	// sizeof(struct cred): 92 bytes, SLAB_HWCACHE_ALIGN: 0x00002000UL, SLAB_PANIC: 0x00040000UL
	// kmem_cache_create("cred_jar", 92, 0, 0x00042000, NULL): kmem_cache#16
	cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
				     0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
	// cred_jar: kmem_cache#16
}

/**
 * prepare_kernel_cred - Prepare a set of credentials for a kernel service
 * @daemon: A userspace daemon to be used as a reference
 *
 * Prepare a set of credentials for a kernel service.  This can then be used to
 * override a task's own credentials so that work can be done on behalf of that
 * task that requires a different subjective context.
 *
 * @daemon is used to provide a base for the security record, but can be NULL.
 * If @daemon is supplied, then the security data will be derived from that;
 * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
 *
 * The caller may change these controls afterwards if desired.
 *
 * Returns the new credentials or NULL if out of memory.
 *
 * Does not take, and does not return holding current->cred_replace_mutex.
 */
struct cred *prepare_kernel_cred(struct task_struct *daemon)
{
	const struct cred *old;
	struct cred *new;

	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
	if (!new)
		return NULL;

	kdebug("prepare_kernel_cred() alloc %p", new);

	if (daemon)
		old = get_task_cred(daemon);
	else
		old = get_cred(&init_cred);

	validate_creds(old);

	*new = *old;
	atomic_set(&new->usage, 1);
	set_cred_subscribers(new, 0);
	get_uid(new->user);
	get_user_ns(new->user_ns);
	get_group_info(new->group_info);

#ifdef CONFIG_KEYS
	new->session_keyring = NULL;
	new->process_keyring = NULL;
	new->thread_keyring = NULL;
	new->request_key_auth = NULL;
	new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
#endif

#ifdef CONFIG_SECURITY
	new->security = NULL;
#endif
	if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
		goto error;

	put_cred(old);
	validate_creds(new);
	return new;

error:
	put_cred(new);
	put_cred(old);
	return NULL;
}
EXPORT_SYMBOL(prepare_kernel_cred);

/**
 * set_security_override - Set the security ID in a set of credentials
 * @new: The credentials to alter
 * @secid: The LSM security ID to set
 *
 * Set the LSM security ID in a set of credentials so that the subjective
 * security is overridden when an alternative set of credentials is used.
 */
int set_security_override(struct cred *new, u32 secid)
{
	return security_kernel_act_as(new, secid);
}
EXPORT_SYMBOL(set_security_override);

/**
 * set_security_override_from_ctx - Set the security ID in a set of credentials
 * @new: The credentials to alter
 * @secctx: The LSM security context to generate the security ID from.
 *
 * Set the LSM security ID in a set of credentials so that the subjective
 * security is overridden when an alternative set of credentials is used.  The
 * security ID is specified in string form as a security context to be
 * interpreted by the LSM.
 */
int set_security_override_from_ctx(struct cred *new, const char *secctx)
{
	u32 secid;
	int ret;

	ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
	if (ret < 0)
		return ret;

	return set_security_override(new, secid);
}
EXPORT_SYMBOL(set_security_override_from_ctx);

/**
 * set_create_files_as - Set the LSM file create context in a set of credentials
 * @new: The credentials to alter
 * @inode: The inode to take the context from
 *
 * Change the LSM file creation context in a set of credentials to be the same
 * as the object context of the specified inode, so that the new inodes have
 * the same MAC context as that inode.
 */
int set_create_files_as(struct cred *new, struct inode *inode)
{
	new->fsuid = inode->i_uid;
	new->fsgid = inode->i_gid;
	return security_kernel_create_files_as(new, inode);
}
EXPORT_SYMBOL(set_create_files_as);

#ifdef CONFIG_DEBUG_CREDENTIALS

bool creds_are_invalid(const struct cred *cred)
{
	if (cred->magic != CRED_MAGIC)
		return true;
#ifdef CONFIG_SECURITY_SELINUX
	/*
	 * cred->security == NULL if security_cred_alloc_blank() or
	 * security_prepare_creds() returned an error.
	 */
	if (selinux_is_enabled() && cred->security) {
		if ((unsigned long) cred->security < PAGE_SIZE)
			return true;
		if ((*(u32 *)cred->security & 0xffffff00) ==
		    (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
			return true;
	}
#endif
	return false;
}
EXPORT_SYMBOL(creds_are_invalid);

/*
 * dump invalid credentials
 */
static void dump_invalid_creds(const struct cred *cred, const char *label,
			       const struct task_struct *tsk)
{
	printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
	       label, cred,
	       cred == &init_cred ? "[init]" : "",
	       cred == tsk->real_cred ? "[real]" : "",
	       cred == tsk->cred ? "[eff]" : "");
	printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
	       cred->magic, cred->put_addr);
	printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
	       atomic_read(&cred->usage),
	       read_cred_subscribers(cred));
	printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
		from_kuid_munged(&init_user_ns, cred->uid),
		from_kuid_munged(&init_user_ns, cred->euid),
		from_kuid_munged(&init_user_ns, cred->suid),
		from_kuid_munged(&init_user_ns, cred->fsuid));
	printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
		from_kgid_munged(&init_user_ns, cred->gid),
		from_kgid_munged(&init_user_ns, cred->egid),
		from_kgid_munged(&init_user_ns, cred->sgid),
		from_kgid_munged(&init_user_ns, cred->fsgid));
#ifdef CONFIG_SECURITY
	printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
	if ((unsigned long) cred->security >= PAGE_SIZE &&
	    (((unsigned long) cred->security & 0xffffff00) !=
	     (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
		printk(KERN_ERR "CRED: ->security {%x, %x}\n",
		       ((u32*)cred->security)[0],
		       ((u32*)cred->security)[1]);
#endif
}

/*
 * report use of invalid credentials
 */
void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
{
	printk(KERN_ERR "CRED: Invalid credentials\n");
	printk(KERN_ERR "CRED: At %s:%u\n", file, line);
	dump_invalid_creds(cred, "Specified", current);
	BUG();
}
EXPORT_SYMBOL(__invalid_creds);

/*
 * check the credentials on a process
 */
void __validate_process_creds(struct task_struct *tsk,
			      const char *file, unsigned line)
{
	if (tsk->cred == tsk->real_cred) {
		if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
			     creds_are_invalid(tsk->cred)))
			goto invalid_creds;
	} else {
		if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
			     read_cred_subscribers(tsk->cred) < 1 ||
			     creds_are_invalid(tsk->real_cred) ||
			     creds_are_invalid(tsk->cred)))
			goto invalid_creds;
	}
	return;

invalid_creds:
	printk(KERN_ERR "CRED: Invalid process credentials\n");
	printk(KERN_ERR "CRED: At %s:%u\n", file, line);

	dump_invalid_creds(tsk->real_cred, "Real", tsk);
	if (tsk->cred != tsk->real_cred)
		dump_invalid_creds(tsk->cred, "Effective", tsk);
	else
		printk(KERN_ERR "CRED: Effective creds == Real creds\n");
	BUG();
}
EXPORT_SYMBOL(__validate_process_creds);

/*
 * check creds for do_exit()
 */
void validate_creds_for_do_exit(struct task_struct *tsk)
{
	kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
	       tsk->real_cred, tsk->cred,
	       atomic_read(&tsk->cred->usage),
	       read_cred_subscribers(tsk->cred));

	__validate_process_creds(tsk, __FILE__, __LINE__);
}

#endif /* CONFIG_DEBUG_CREDENTIALS */