security/yama/yama_lsm.c - third_party/linux - Git at Google

 /*
  * Yama Linux Security Module
  *
  * Author: Kees Cook <keescook@chromium.org>
  *
  * Copyright (C) 2010 Canonical, Ltd.
  * Copyright (C) 2011 The Chromium OS Authors.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2, as
  * published by the Free Software Foundation.
  *
  */

 #include <linux/lsm_hooks.h>
 #include <linux/sysctl.h>
 #include <linux/ptrace.h>
 #include <linux/prctl.h>
 #include <linux/ratelimit.h>
 #include <linux/workqueue.h>
 #include <linux/string_helpers.h>
 #include <linux/task_work.h>
 #include <linux/sched.h>
 #include <linux/spinlock.h>

 #define YAMA_SCOPE_DISABLED	0
 #define YAMA_SCOPE_RELATIONAL	1
 #define YAMA_SCOPE_CAPABILITY	2
 #define YAMA_SCOPE_NO_ATTACH	3

 static int ptrace_scope = YAMA_SCOPE_RELATIONAL;

 /* describe a ptrace relationship for potential exception */
 struct ptrace_relation {
 	struct task_struct *tracer;
 	struct task_struct *tracee;
 	bool invalid;
 	struct list_head node;
 	struct rcu_head rcu;
 };

 static LIST_HEAD(ptracer_relations);
 static DEFINE_SPINLOCK(ptracer_relations_lock);

 static void yama_relation_cleanup(struct work_struct *work);
 static DECLARE_WORK(yama_relation_work, yama_relation_cleanup);

 struct access_report_info {
 	struct callback_head work;
 	const char *access;
 	struct task_struct *target;
 	struct task_struct *agent;
 };

 static void __report_access(struct callback_head *work)
 {
 	struct access_report_info *info =
 		container_of(work, struct access_report_info, work);
 	char *target_cmd, *agent_cmd;

 	target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL);
 	agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL);

 	pr_notice_ratelimited(
 		"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
 		info->access, target_cmd, info->target->pid, agent_cmd,
 		info->agent->pid);

 	kfree(agent_cmd);
 	kfree(target_cmd);

 	put_task_struct(info->agent);
 	put_task_struct(info->target);
 	kfree(info);
 }

 /* defers execution because cmdline access can sleep */
 static void report_access(const char *access, struct task_struct *target,
 				struct task_struct *agent)
 {
 	struct access_report_info *info;
 	char agent_comm[sizeof(agent->comm)];

 	assert_spin_locked(&target->alloc_lock); /* for target->comm */

 	if (current->flags & PF_KTHREAD) {
 		/* I don't think kthreads call task_work_run() before exiting.
 		 * Imagine angry ranting about procfs here.
 		 */
 		pr_notice_ratelimited(
 		    "ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
 		    access, target->comm, target->pid,
 		    get_task_comm(agent_comm, agent), agent->pid);
 		return;
 	}

 	info = kmalloc(sizeof(*info), GFP_ATOMIC);
 	if (!info)
 		return;
 	init_task_work(&info->work, __report_access);
 	get_task_struct(target);
 	get_task_struct(agent);
 	info->access = access;
 	info->target = target;
 	info->agent = agent;
 	if (task_work_add(current, &info->work, true) == 0)
 		return; /* success */

 	WARN(1, "report_access called from exiting task");
 	put_task_struct(target);
 	put_task_struct(agent);
 	kfree(info);
 }

 /**
  * yama_relation_cleanup - remove invalid entries from the relation list
  *
  */
 static void yama_relation_cleanup(struct work_struct *work)
 {
 	struct ptrace_relation *relation;

 	spin_lock(&ptracer_relations_lock);
 	rcu_read_lock();
 	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
 		if (relation->invalid) {
 			list_del_rcu(&relation->node);
 			kfree_rcu(relation, rcu);
 		}
 	}
 	rcu_read_unlock();
 	spin_unlock(&ptracer_relations_lock);
 }

 /**
  * yama_ptracer_add - add/replace an exception for this tracer/tracee pair
  * @tracer: the task_struct of the process doing the ptrace
  * @tracee: the task_struct of the process to be ptraced
  *
  * Each tracee can have, at most, one tracer registered. Each time this
  * is called, the prior registered tracer will be replaced for the tracee.
  *
  * Returns 0 if relationship was added, -ve on error.
  */
 static int yama_ptracer_add(struct task_struct *tracer,
 			    struct task_struct *tracee)
 {
 	struct ptrace_relation *relation, *added;

 	added = kmalloc(sizeof(*added), GFP_KERNEL);
 	if (!added)
 		return -ENOMEM;

 	added->tracee = tracee;
 	added->tracer = tracer;
 	added->invalid = false;

 	spin_lock(&ptracer_relations_lock);
 	rcu_read_lock();
 	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
 		if (relation->invalid)
 			continue;
 		if (relation->tracee == tracee) {
 			list_replace_rcu(&relation->node, &added->node);
 			kfree_rcu(relation, rcu);
 			goto out;
 		}
 	}

 	list_add_rcu(&added->node, &ptracer_relations);

 out:
 	rcu_read_unlock();
 	spin_unlock(&ptracer_relations_lock);
 	return 0;
 }

 /**
  * yama_ptracer_del - remove exceptions related to the given tasks
  * @tracer: remove any relation where tracer task matches
  * @tracee: remove any relation where tracee task matches
  */
 static void yama_ptracer_del(struct task_struct *tracer,
 			     struct task_struct *tracee)
 {
 	struct ptrace_relation *relation;
 	bool marked = false;

 	rcu_read_lock();
 	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
 		if (relation->invalid)
 			continue;
 		if (relation->tracee == tracee ||
 		    (tracer && relation->tracer == tracer)) {
 			relation->invalid = true;
 			marked = true;
 		}
 	}
 	rcu_read_unlock();

 	if (marked)
 		schedule_work(&yama_relation_work);
 }

 /**
  * yama_task_free - check for task_pid to remove from exception list
  * @task: task being removed
  */
 void yama_task_free(struct task_struct *task)
 {
 	yama_ptracer_del(task, task);
 }

 /**
  * yama_task_prctl - check for Yama-specific prctl operations
  * @option: operation
  * @arg2: argument
  * @arg3: argument
  * @arg4: argument
  * @arg5: argument
  *
  * Return 0 on success, -ve on error.  -ENOSYS is returned when Yama
  * does not handle the given option.
  */
 int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 			   unsigned long arg4, unsigned long arg5)
 {
 	int rc = -ENOSYS;
 	struct task_struct *myself = current;

 	switch (option) {
 	case PR_SET_PTRACER:
 		/* Since a thread can call prctl(), find the group leader
 		 * before calling _add() or _del() on it, since we want
 		 * process-level granularity of control. The tracer group
 		 * leader checking is handled later when walking the ancestry
 		 * at the time of PTRACE_ATTACH check.
 		 */
 		rcu_read_lock();
 		if (!thread_group_leader(myself))
 			myself = rcu_dereference(myself->group_leader);
 		get_task_struct(myself);
 		rcu_read_unlock();

 		if (arg2 == 0) {
 			yama_ptracer_del(NULL, myself);
 			rc = 0;
 		} else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) {
 			rc = yama_ptracer_add(NULL, myself);
 		} else {
 			struct task_struct *tracer;

 			tracer = find_get_task_by_vpid(arg2);
 			if (!tracer) {
 				rc = -EINVAL;
 			} else {
 				rc = yama_ptracer_add(tracer, myself);
 				put_task_struct(tracer);
 			}
 		}

 		put_task_struct(myself);
 		break;
 	}

 	return rc;
 }

 /**
  * task_is_descendant - walk up a process family tree looking for a match
  * @parent: the process to compare against while walking up from child
  * @child: the process to start from while looking upwards for parent
  *
  * Returns 1 if child is a descendant of parent, 0 if not.
  */
 static int task_is_descendant(struct task_struct *parent,
 			      struct task_struct *child)
 {
 	int rc = 0;
 	struct task_struct *walker = child;

 	if (!parent || !child)
 		return 0;

 	rcu_read_lock();
 	if (!thread_group_leader(parent))
 		parent = rcu_dereference(parent->group_leader);
 	while (walker->pid > 0) {
 		if (!thread_group_leader(walker))
 			walker = rcu_dereference(walker->group_leader);
 		if (walker == parent) {
 			rc = 1;
 			break;
 		}
 		walker = rcu_dereference(walker->real_parent);
 	}
 	rcu_read_unlock();

 	return rc;
 }

 /**
  * ptracer_exception_found - tracer registered as exception for this tracee
  * @tracer: the task_struct of the process attempting ptrace
  * @tracee: the task_struct of the process to be ptraced
  *
  * Returns 1 if tracer has a ptracer exception ancestor for tracee.
  */
 static int ptracer_exception_found(struct task_struct *tracer,
 				   struct task_struct *tracee)
 {
 	int rc = 0;
 	struct ptrace_relation *relation;
 	struct task_struct *parent = NULL;
 	bool found = false;

 	rcu_read_lock();

 	/*
 	 * If there's already an active tracing relationship, then make an
 	 * exception for the sake of other accesses, like process_vm_rw().
 	 */
 	parent = ptrace_parent(tracee);
 	if (parent != NULL && same_thread_group(parent, tracer)) {
 		rc = 1;
 		goto unlock;
 	}

 	/* Look for a PR_SET_PTRACER relationship. */
 	if (!thread_group_leader(tracee))
 		tracee = rcu_dereference(tracee->group_leader);
 	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
 		if (relation->invalid)
 			continue;
 		if (relation->tracee == tracee) {
 			parent = relation->tracer;
 			found = true;
 			break;
 		}
 	}

 	if (found && (parent == NULL || task_is_descendant(parent, tracer)))
 		rc = 1;

 unlock:
 	rcu_read_unlock();

 	return rc;
 }

 /**
  * yama_ptrace_access_check - validate PTRACE_ATTACH calls
  * @child: task that current task is attempting to ptrace
  * @mode: ptrace attach mode
  *
  * Returns 0 if following the ptrace is allowed, -ve on error.
  */
 static int yama_ptrace_access_check(struct task_struct *child,
 				    unsigned int mode)
 {
 	int rc = 0;

 	/* require ptrace target be a child of ptracer on attach */
 	if (mode & PTRACE_MODE_ATTACH) {
 		switch (ptrace_scope) {
 		case YAMA_SCOPE_DISABLED:
 			/* No additional restrictions. */
 			break;
 		case YAMA_SCOPE_RELATIONAL:
 			rcu_read_lock();
 			if (!task_is_descendant(current, child) &&
 			    !ptracer_exception_found(current, child) &&
 			    !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
 				rc = -EPERM;
 			rcu_read_unlock();
 			break;
 		case YAMA_SCOPE_CAPABILITY:
 			rcu_read_lock();
 			if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
 				rc = -EPERM;
 			rcu_read_unlock();
 			break;
 		case YAMA_SCOPE_NO_ATTACH:
 		default:
 			rc = -EPERM;
 			break;
 		}
 	}

 	if (rc && (mode & PTRACE_MODE_NOAUDIT) == 0)
 		report_access("attach", child, current);

 	return rc;
 }

 /**
  * yama_ptrace_traceme - validate PTRACE_TRACEME calls
  * @parent: task that will become the ptracer of the current task
  *
  * Returns 0 if following the ptrace is allowed, -ve on error.
  */
 int yama_ptrace_traceme(struct task_struct *parent)
 {
 	int rc = 0;

 	/* Only disallow PTRACE_TRACEME on more aggressive settings. */
 	switch (ptrace_scope) {
 	case YAMA_SCOPE_CAPABILITY:
 		if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE))
 			rc = -EPERM;
 		break;
 	case YAMA_SCOPE_NO_ATTACH:
 		rc = -EPERM;
 		break;
 	}

 	if (rc) {
 		task_lock(current);
 		report_access("traceme", current, parent);
 		task_unlock(current);
 	}

 	return rc;
 }

 static struct security_hook_list yama_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check),
 	LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme),
 	LSM_HOOK_INIT(task_prctl, yama_task_prctl),
 	LSM_HOOK_INIT(task_free, yama_task_free),
 };

 #ifdef CONFIG_SYSCTL
 static int yama_dointvec_minmax(struct ctl_table *table, int write,
 				void __user *buffer, size_t *lenp, loff_t *ppos)
 {
 	struct ctl_table table_copy;

 	if (write && !capable(CAP_SYS_PTRACE))
 		return -EPERM;

 	/* Lock the max value if it ever gets set. */
 	table_copy = *table;
 	if (*(int *)table_copy.data == *(int *)table_copy.extra2)
 		table_copy.extra1 = table_copy.extra2;

 	return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
 }

 static int zero;
 static int max_scope = YAMA_SCOPE_NO_ATTACH;

 struct ctl_path yama_sysctl_path[] = {
 	{ .procname = "kernel", },
 	{ .procname = "yama", },
 	{ }
 };

 static struct ctl_table yama_sysctl_table[] = {
 	{
 		.procname       = "ptrace_scope",
 		.data           = &ptrace_scope,
 		.maxlen         = sizeof(int),
 		.mode           = 0644,
 		.proc_handler   = yama_dointvec_minmax,
 		.extra1         = &zero,
 		.extra2         = &max_scope,
 	},
 	{ }
 };
 static void __init yama_init_sysctl(void)
 {
 	if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
 		panic("Yama: sysctl registration failed.\n");
 }
 #else
 static inline void yama_init_sysctl(void) { }
 #endif /* CONFIG_SYSCTL */

 void __init yama_add_hooks(void)
 {
 	pr_info("Yama: becoming mindful.\n");
 	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama");
 	yama_init_sysctl();
 }
	/*
	* Yama Linux Security Module
	*
	* Author: Kees Cook <keescook@chromium.org>
	*
	* Copyright (C) 2010 Canonical, Ltd.
	* Copyright (C) 2011 The Chromium OS Authors.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2, as
	* published by the Free Software Foundation.
	*
	*/

	#include <linux/lsm_hooks.h>
	#include <linux/sysctl.h>
	#include <linux/ptrace.h>
	#include <linux/prctl.h>
	#include <linux/ratelimit.h>
	#include <linux/workqueue.h>
	#include <linux/string_helpers.h>
	#include <linux/task_work.h>
	#include <linux/sched.h>
	#include <linux/spinlock.h>

	#define YAMA_SCOPE_DISABLED 0
	#define YAMA_SCOPE_RELATIONAL 1
	#define YAMA_SCOPE_CAPABILITY 2
	#define YAMA_SCOPE_NO_ATTACH 3

	static int ptrace_scope = YAMA_SCOPE_RELATIONAL;

	/* describe a ptrace relationship for potential exception */
	struct ptrace_relation {
	struct task_struct *tracer;
	struct task_struct *tracee;
	bool invalid;
	struct list_head node;
	struct rcu_head rcu;
	};

	static LIST_HEAD(ptracer_relations);
	static DEFINE_SPINLOCK(ptracer_relations_lock);

	static void yama_relation_cleanup(struct work_struct *work);
	static DECLARE_WORK(yama_relation_work, yama_relation_cleanup);

	struct access_report_info {
	struct callback_head work;
	const char *access;
	struct task_struct *target;
	struct task_struct *agent;
	};

	static void __report_access(struct callback_head *work)
	{
	struct access_report_info *info =
	container_of(work, struct access_report_info, work);
	char target_cmd, agent_cmd;

	target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL);
	agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL);

	pr_notice_ratelimited(
	"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
	info->access, target_cmd, info->target->pid, agent_cmd,
	info->agent->pid);

	kfree(agent_cmd);
	kfree(target_cmd);

	put_task_struct(info->agent);
	put_task_struct(info->target);
	kfree(info);
	}

	/* defers execution because cmdline access can sleep */
	static void report_access(const char access, struct task_struct target,
	struct task_struct *agent)
	{
	struct access_report_info *info;
	char agent_comm[sizeof(agent->comm)];

	assert_spin_locked(&target->alloc_lock); /* for target->comm */

	if (current->flags & PF_KTHREAD) {
	/* I don't think kthreads call task_work_run() before exiting.
	* Imagine angry ranting about procfs here.
	*/
	pr_notice_ratelimited(
	"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
	access, target->comm, target->pid,
	get_task_comm(agent_comm, agent), agent->pid);
	return;
	}

	info = kmalloc(sizeof(*info), GFP_ATOMIC);
	if (!info)
	return;
	init_task_work(&info->work, __report_access);
	get_task_struct(target);
	get_task_struct(agent);
	info->access = access;
	info->target = target;
	info->agent = agent;
	if (task_work_add(current, &info->work, true) == 0)
	return; /* success */

	WARN(1, "report_access called from exiting task");
	put_task_struct(target);
	put_task_struct(agent);
	kfree(info);
	}

	/**
	* yama_relation_cleanup - remove invalid entries from the relation list
	*
	*/
	static void yama_relation_cleanup(struct work_struct *work)
	{
	struct ptrace_relation *relation;

	spin_lock(&ptracer_relations_lock);
	rcu_read_lock();
	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
	if (relation->invalid) {
	list_del_rcu(&relation->node);
	kfree_rcu(relation, rcu);
	}
	}
	rcu_read_unlock();
	spin_unlock(&ptracer_relations_lock);
	}

	/**
	* yama_ptracer_add - add/replace an exception for this tracer/tracee pair
	* @tracer: the task_struct of the process doing the ptrace
	* @tracee: the task_struct of the process to be ptraced
	*
	* Each tracee can have, at most, one tracer registered. Each time this
	* is called, the prior registered tracer will be replaced for the tracee.
	*
	* Returns 0 if relationship was added, -ve on error.
	*/
	static int yama_ptracer_add(struct task_struct *tracer,
	struct task_struct *tracee)
	{
	struct ptrace_relation relation, added;

	added = kmalloc(sizeof(*added), GFP_KERNEL);
	if (!added)
	return -ENOMEM;

	added->tracee = tracee;
	added->tracer = tracer;
	added->invalid = false;

	spin_lock(&ptracer_relations_lock);
	rcu_read_lock();
	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
	if (relation->invalid)
	continue;
	if (relation->tracee == tracee) {
	list_replace_rcu(&relation->node, &added->node);
	kfree_rcu(relation, rcu);
	goto out;
	}
	}

	list_add_rcu(&added->node, &ptracer_relations);

	out:
	rcu_read_unlock();
	spin_unlock(&ptracer_relations_lock);
	return 0;
	}

	/**
	* yama_ptracer_del - remove exceptions related to the given tasks
	* @tracer: remove any relation where tracer task matches
	* @tracee: remove any relation where tracee task matches
	*/
	static void yama_ptracer_del(struct task_struct *tracer,
	struct task_struct *tracee)
	{
	struct ptrace_relation *relation;
	bool marked = false;

	rcu_read_lock();
	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
	if (relation->invalid)
	continue;
	if (relation->tracee == tracee \|\|
	(tracer && relation->tracer == tracer)) {
	relation->invalid = true;
	marked = true;
	}
	}
	rcu_read_unlock();

	if (marked)
	schedule_work(&yama_relation_work);
	}

	/**
	* yama_task_free - check for task_pid to remove from exception list
	* @task: task being removed
	*/
	void yama_task_free(struct task_struct *task)
	{
	yama_ptracer_del(task, task);
	}

	/**
	* yama_task_prctl - check for Yama-specific prctl operations
	* @option: operation
	* @arg2: argument
	* @arg3: argument
	* @arg4: argument
	* @arg5: argument
	*
	* Return 0 on success, -ve on error. -ENOSYS is returned when Yama
	* does not handle the given option.
	*/
	int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
	unsigned long arg4, unsigned long arg5)
	{
	int rc = -ENOSYS;
	struct task_struct *myself = current;

	switch (option) {
	case PR_SET_PTRACER:
	/* Since a thread can call prctl(), find the group leader
	* before calling _add() or _del() on it, since we want
	* process-level granularity of control. The tracer group
	* leader checking is handled later when walking the ancestry
	* at the time of PTRACE_ATTACH check.
	*/
	rcu_read_lock();
	if (!thread_group_leader(myself))
	myself = rcu_dereference(myself->group_leader);
	get_task_struct(myself);
	rcu_read_unlock();

	if (arg2 == 0) {
	yama_ptracer_del(NULL, myself);
	rc = 0;
	} else if (arg2 == PR_SET_PTRACER_ANY \|\| (int)arg2 == -1) {
	rc = yama_ptracer_add(NULL, myself);
	} else {
	struct task_struct *tracer;

	tracer = find_get_task_by_vpid(arg2);
	if (!tracer) {
	rc = -EINVAL;
	} else {
	rc = yama_ptracer_add(tracer, myself);
	put_task_struct(tracer);
	}
	}

	put_task_struct(myself);
	break;
	}

	return rc;
	}

	/**
	* task_is_descendant - walk up a process family tree looking for a match
	* @parent: the process to compare against while walking up from child
	* @child: the process to start from while looking upwards for parent
	*
	* Returns 1 if child is a descendant of parent, 0 if not.
	*/
	static int task_is_descendant(struct task_struct *parent,
	struct task_struct *child)
	{
	int rc = 0;
	struct task_struct *walker = child;

	if (!parent \|\| !child)
	return 0;

	rcu_read_lock();
	if (!thread_group_leader(parent))
	parent = rcu_dereference(parent->group_leader);
	while (walker->pid > 0) {
	if (!thread_group_leader(walker))
	walker = rcu_dereference(walker->group_leader);
	if (walker == parent) {
	rc = 1;
	break;
	}
	walker = rcu_dereference(walker->real_parent);
	}
	rcu_read_unlock();

	return rc;
	}

	/**
	* ptracer_exception_found - tracer registered as exception for this tracee
	* @tracer: the task_struct of the process attempting ptrace
	* @tracee: the task_struct of the process to be ptraced
	*
	* Returns 1 if tracer has a ptracer exception ancestor for tracee.
	*/
	static int ptracer_exception_found(struct task_struct *tracer,
	struct task_struct *tracee)
	{
	int rc = 0;
	struct ptrace_relation *relation;
	struct task_struct *parent = NULL;
	bool found = false;

	rcu_read_lock();

	/*
	* If there's already an active tracing relationship, then make an
	* exception for the sake of other accesses, like process_vm_rw().
	*/
	parent = ptrace_parent(tracee);
	if (parent != NULL && same_thread_group(parent, tracer)) {
	rc = 1;
	goto unlock;
	}

	/* Look for a PR_SET_PTRACER relationship. */
	if (!thread_group_leader(tracee))
	tracee = rcu_dereference(tracee->group_leader);
	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
	if (relation->invalid)
	continue;
	if (relation->tracee == tracee) {
	parent = relation->tracer;
	found = true;
	break;
	}
	}

	if (found && (parent == NULL \|\| task_is_descendant(parent, tracer)))
	rc = 1;

	unlock:
	rcu_read_unlock();

	return rc;
	}

	/**
	* yama_ptrace_access_check - validate PTRACE_ATTACH calls
	* @child: task that current task is attempting to ptrace
	* @mode: ptrace attach mode
	*
	* Returns 0 if following the ptrace is allowed, -ve on error.
	*/
	static int yama_ptrace_access_check(struct task_struct *child,
	unsigned int mode)
	{
	int rc = 0;

	/* require ptrace target be a child of ptracer on attach */
	if (mode & PTRACE_MODE_ATTACH) {
	switch (ptrace_scope) {
	case YAMA_SCOPE_DISABLED:
	/* No additional restrictions. */
	break;
	case YAMA_SCOPE_RELATIONAL:
	rcu_read_lock();
	if (!task_is_descendant(current, child) &&
	!ptracer_exception_found(current, child) &&
	!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
	rc = -EPERM;
	rcu_read_unlock();
	break;
	case YAMA_SCOPE_CAPABILITY:
	rcu_read_lock();
	if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
	rc = -EPERM;
	rcu_read_unlock();
	break;
	case YAMA_SCOPE_NO_ATTACH:
	default:
	rc = -EPERM;
	break;
	}
	}

	if (rc && (mode & PTRACE_MODE_NOAUDIT) == 0)
	report_access("attach", child, current);

	return rc;
	}

	/**
	* yama_ptrace_traceme - validate PTRACE_TRACEME calls
	* @parent: task that will become the ptracer of the current task
	*
	* Returns 0 if following the ptrace is allowed, -ve on error.
	*/
	int yama_ptrace_traceme(struct task_struct *parent)
	{
	int rc = 0;

	/* Only disallow PTRACE_TRACEME on more aggressive settings. */
	switch (ptrace_scope) {
	case YAMA_SCOPE_CAPABILITY:
	if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE))
	rc = -EPERM;
	break;
	case YAMA_SCOPE_NO_ATTACH:
	rc = -EPERM;
	break;
	}

	if (rc) {
	task_lock(current);
	report_access("traceme", current, parent);
	task_unlock(current);
	}

	return rc;
	}

	static struct security_hook_list yama_hooks[] __lsm_ro_after_init = {
	LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check),
	LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme),
	LSM_HOOK_INIT(task_prctl, yama_task_prctl),
	LSM_HOOK_INIT(task_free, yama_task_free),
	};

	#ifdef CONFIG_SYSCTL
	static int yama_dointvec_minmax(struct ctl_table *table, int write,
	void __user buffer, size_t lenp, loff_t *ppos)
	{
	struct ctl_table table_copy;

	if (write && !capable(CAP_SYS_PTRACE))
	return -EPERM;

	/* Lock the max value if it ever gets set. */
	table_copy = *table;
	if ((int )table_copy.data == (int )table_copy.extra2)
	table_copy.extra1 = table_copy.extra2;

	return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
	}

	static int zero;
	static int max_scope = YAMA_SCOPE_NO_ATTACH;

	struct ctl_path yama_sysctl_path[] = {
	{ .procname = "kernel", },
	{ .procname = "yama", },
	{ }
	};

	static struct ctl_table yama_sysctl_table[] = {
	{
	.procname = "ptrace_scope",
	.data = &ptrace_scope,
	.maxlen = sizeof(int),
	.mode = 0644,
	.proc_handler = yama_dointvec_minmax,
	.extra1 = &zero,
	.extra2 = &max_scope,
	},
	{ }
	};
	static void __init yama_init_sysctl(void)
	{
	if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
	panic("Yama: sysctl registration failed.\n");
	}
	#else
	static inline void yama_init_sysctl(void) { }
	#endif /* CONFIG_SYSCTL */

	void __init yama_add_hooks(void)
	{
	pr_info("Yama: becoming mindful.\n");
	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama");
	yama_init_sysctl();
	}