[linux-2.6-block.git] / security / yama / yama_lsm.c

/*
 * 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;

			rcu_read_lock();
			tracer = find_task_by_vpid(arg2);
			if (tracer)
				get_task_struct(tracer);
			else
				rc = -EINVAL;
			rcu_read_unlock();

			if (tracer) {
				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 is 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 (!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;
	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_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_init_sysctl();
}
Commit	Line	Data
2d514487 KC	1	/*
	2	* Yama Linux Security Module
	3	*
	4	* Author: Kees Cook <keescook@chromium.org>
	5	*
	6	* Copyright (C) 2010 Canonical, Ltd.
	7	* Copyright (C) 2011 The Chromium OS Authors.
	8	*
	9	* This program is free software; you can redistribute it and/or modify
	10	* it under the terms of the GNU General Public License version 2, as
	11	* published by the Free Software Foundation.
	12	*
	13	*/
	14
3c4ed7bd	15	#include <linux/lsm_hooks.h>
2d514487 KC	16	#include <linux/sysctl.h>
	17	#include <linux/ptrace.h>
	18	#include <linux/prctl.h>
	19	#include <linux/ratelimit.h>
235e7527	20	#include <linux/workqueue.h>
8a56038c	21	#include <linux/string_helpers.h>
dca6b414 JH	22	#include <linux/task_work.h>
	23	#include <linux/sched.h>
	24	#include <linux/spinlock.h>
2d514487	25
389da25f KC	26	#define YAMA_SCOPE_DISABLED 0
	27	#define YAMA_SCOPE_RELATIONAL 1
	28	#define YAMA_SCOPE_CAPABILITY 2
	29	#define YAMA_SCOPE_NO_ATTACH 3
	30
	31	static int ptrace_scope = YAMA_SCOPE_RELATIONAL;
2d514487 KC	32
	33	/* describe a ptrace relationship for potential exception */
	34	struct ptrace_relation {
	35	struct task_struct *tracer;
	36	struct task_struct *tracee;
235e7527	37	bool invalid;
2d514487	38	struct list_head node;
93b69d43	39	struct rcu_head rcu;
2d514487 KC	40	};
	41
	42	static LIST_HEAD(ptracer_relations);
	43	static DEFINE_SPINLOCK(ptracer_relations_lock);
	44
235e7527 KC	45	static void yama_relation_cleanup(struct work_struct *work);
	46	static DECLARE_WORK(yama_relation_work, yama_relation_cleanup);
	47
dca6b414 JH	48	struct access_report_info {
	49	struct callback_head work;
	50	const char *access;
	51	struct task_struct *target;
	52	struct task_struct *agent;
	53	};
	54
	55	static void __report_access(struct callback_head *work)
8a56038c	56	{
dca6b414 JH	57	struct access_report_info *info =
dca6b414 JH	58	container_of(work, struct access_report_info, work);
8a56038c KC	59	char target_cmd, agent_cmd;
8a56038c KC	60
dca6b414 JH	61	target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL);
dca6b414 JH	62	agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL);
8a56038c KC	63
	64	pr_notice_ratelimited(
	65	"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
dca6b414 JH	66	info->access, target_cmd, info->target->pid, agent_cmd,
dca6b414 JH	67	info->agent->pid);
8a56038c KC	68
	69	kfree(agent_cmd);
	70	kfree(target_cmd);
dca6b414 JH	71
	72	put_task_struct(info->agent);
	73	put_task_struct(info->target);
	74	kfree(info);
	75	}
	76
	77	/* defers execution because cmdline access can sleep */
	78	static void report_access(const char access, struct task_struct target,
	79	struct task_struct *agent)
	80	{
	81	struct access_report_info *info;
	82	char agent_comm[sizeof(agent->comm)];
	83
	84	assert_spin_locked(&target->alloc_lock); /* for target->comm */
	85
	86	if (current->flags & PF_KTHREAD) {
	87	/* I don't think kthreads call task_work_run() before exiting.
	88	* Imagine angry ranting about procfs here.
	89	*/
	90	pr_notice_ratelimited(
	91	"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
	92	access, target->comm, target->pid,
	93	get_task_comm(agent_comm, agent), agent->pid);
	94	return;
	95	}
	96
	97	info = kmalloc(sizeof(*info), GFP_ATOMIC);
	98	if (!info)
	99	return;
	100	init_task_work(&info->work, __report_access);
	101	get_task_struct(target);
	102	get_task_struct(agent);
	103	info->access = access;
	104	info->target = target;
	105	info->agent = agent;
	106	if (task_work_add(current, &info->work, true) == 0)
	107	return; /* success */
	108
	109	WARN(1, "report_access called from exiting task");
	110	put_task_struct(target);
	111	put_task_struct(agent);
	112	kfree(info);
8a56038c KC	113	}
8a56038c KC	114
235e7527 KC	115	/**
	116	* yama_relation_cleanup - remove invalid entries from the relation list
	117	*
	118	*/
	119	static void yama_relation_cleanup(struct work_struct *work)
	120	{
	121	struct ptrace_relation *relation;
	122
	123	spin_lock(&ptracer_relations_lock);
	124	rcu_read_lock();
	125	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
	126	if (relation->invalid) {
	127	list_del_rcu(&relation->node);
	128	kfree_rcu(relation, rcu);
	129	}
	130	}
	131	rcu_read_unlock();
	132	spin_unlock(&ptracer_relations_lock);
	133	}
	134
2d514487 KC	135	/**
	136	* yama_ptracer_add - add/replace an exception for this tracer/tracee pair
	137	* @tracer: the task_struct of the process doing the ptrace
	138	* @tracee: the task_struct of the process to be ptraced
	139	*
	140	* Each tracee can have, at most, one tracer registered. Each time this
	141	* is called, the prior registered tracer will be replaced for the tracee.
	142	*
	143	* Returns 0 if relationship was added, -ve on error.
	144	*/
	145	static int yama_ptracer_add(struct task_struct *tracer,
	146	struct task_struct *tracee)
	147	{
93b69d43	148	struct ptrace_relation relation, added;
2d514487 KC	149
	150	added = kmalloc(sizeof(*added), GFP_KERNEL);
	151	if (!added)
	152	return -ENOMEM;
	153
93b69d43 KC	154	added->tracee = tracee;
93b69d43 KC	155	added->tracer = tracer;
235e7527	156	added->invalid = false;
93b69d43	157
235e7527	158	spin_lock(&ptracer_relations_lock);
93b69d43 KC	159	rcu_read_lock();
93b69d43 KC	160	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
235e7527 KC	161	if (relation->invalid)
235e7527 KC	162	continue;
93b69d43 KC	163	if (relation->tracee == tracee) {
	164	list_replace_rcu(&relation->node, &added->node);
	165	kfree_rcu(relation, rcu);
	166	goto out;
2d514487	167	}
2d514487	168	}
2d514487	169
93b69d43	170	list_add_rcu(&added->node, &ptracer_relations);
2d514487	171
93b69d43 KC	172	out:
93b69d43 KC	173	rcu_read_unlock();
235e7527	174	spin_unlock(&ptracer_relations_lock);
93b69d43	175	return 0;
2d514487 KC	176	}
	177
	178	/**
	179	* yama_ptracer_del - remove exceptions related to the given tasks
	180	* @tracer: remove any relation where tracer task matches
	181	* @tracee: remove any relation where tracee task matches
	182	*/
	183	static void yama_ptracer_del(struct task_struct *tracer,
	184	struct task_struct *tracee)
	185	{
93b69d43	186	struct ptrace_relation *relation;
235e7527	187	bool marked = false;
2d514487	188
93b69d43 KC	189	rcu_read_lock();
93b69d43 KC	190	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
235e7527 KC	191	if (relation->invalid)
235e7527 KC	192	continue;
2d514487	193	if (relation->tracee == tracee \|\|
bf06189e	194	(tracer && relation->tracer == tracer)) {
235e7527 KC	195	relation->invalid = true;
235e7527 KC	196	marked = true;
2d514487	197	}
93b69d43 KC	198	}
93b69d43 KC	199	rcu_read_unlock();
235e7527 KC	200
	201	if (marked)
	202	schedule_work(&yama_relation_work);
2d514487 KC	203	}
	204
	205	/**
	206	* yama_task_free - check for task_pid to remove from exception list
	207	* @task: task being removed
	208	*/
c6993e4a	209	void yama_task_free(struct task_struct *task)
2d514487 KC	210	{
	211	yama_ptracer_del(task, task);
	212	}
	213
	214	/**
	215	* yama_task_prctl - check for Yama-specific prctl operations
	216	* @option: operation
	217	* @arg2: argument
	218	* @arg3: argument
	219	* @arg4: argument
	220	* @arg5: argument
	221	*
	222	* Return 0 on success, -ve on error. -ENOSYS is returned when Yama
	223	* does not handle the given option.
	224	*/
c6993e4a	225	int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
2d514487 KC	226	unsigned long arg4, unsigned long arg5)
2d514487 KC	227	{
b1d9e6b0	228	int rc = -ENOSYS;
2d514487 KC	229	struct task_struct *myself = current;
2d514487 KC	230
2d514487 KC	231	switch (option) {
	232	case PR_SET_PTRACER:
	233	/* Since a thread can call prctl(), find the group leader
	234	* before calling _add() or _del() on it, since we want
	235	* process-level granularity of control. The tracer group
	236	* leader checking is handled later when walking the ancestry
	237	* at the time of PTRACE_ATTACH check.
	238	*/
	239	rcu_read_lock();
	240	if (!thread_group_leader(myself))
	241	myself = rcu_dereference(myself->group_leader);
	242	get_task_struct(myself);
	243	rcu_read_unlock();
	244
	245	if (arg2 == 0) {
	246	yama_ptracer_del(NULL, myself);
	247	rc = 0;
2e4930eb	248	} else if (arg2 == PR_SET_PTRACER_ANY \|\| (int)arg2 == -1) {
bf06189e	249	rc = yama_ptracer_add(NULL, myself);
2d514487 KC	250	} else {
	251	struct task_struct *tracer;
	252
	253	rcu_read_lock();
	254	tracer = find_task_by_vpid(arg2);
	255	if (tracer)
	256	get_task_struct(tracer);
	257	else
	258	rc = -EINVAL;
	259	rcu_read_unlock();
	260
	261	if (tracer) {
	262	rc = yama_ptracer_add(tracer, myself);
	263	put_task_struct(tracer);
	264	}
	265	}
	266
	267	put_task_struct(myself);
	268	break;
	269	}
	270
	271	return rc;
	272	}
	273
	274	/**
	275	* task_is_descendant - walk up a process family tree looking for a match
	276	* @parent: the process to compare against while walking up from child
	277	* @child: the process to start from while looking upwards for parent
	278	*
	279	* Returns 1 if child is a descendant of parent, 0 if not.
	280	*/
	281	static int task_is_descendant(struct task_struct *parent,
	282	struct task_struct *child)
	283	{
	284	int rc = 0;
	285	struct task_struct *walker = child;
	286
	287	if (!parent \|\| !child)
	288	return 0;
	289
	290	rcu_read_lock();
	291	if (!thread_group_leader(parent))
	292	parent = rcu_dereference(parent->group_leader);
	293	while (walker->pid > 0) {
	294	if (!thread_group_leader(walker))
	295	walker = rcu_dereference(walker->group_leader);
	296	if (walker == parent) {
	297	rc = 1;
	298	break;
	299	}
	300	walker = rcu_dereference(walker->real_parent);
	301	}
	302	rcu_read_unlock();
	303
	304	return rc;
	305	}
	306
	307	/**
	308	* ptracer_exception_found - tracer registered as exception for this tracee
	309	* @tracer: the task_struct of the process attempting ptrace
	310	* @tracee: the task_struct of the process to be ptraced
	311	*
	312	* Returns 1 if tracer has is ptracer exception ancestor for tracee.
	313	*/
314	static int ptracer_exception_found(struct task_struct *tracer,
315	struct task_struct *tracee)
316	{
317	int rc = 0;
318	struct ptrace_relation *relation;
319	struct task_struct *parent = NULL;
bf06189e	320	bool found = false;
2d514487	321
2d514487 KC	322	rcu_read_lock();
	323	if (!thread_group_leader(tracee))
	324	tracee = rcu_dereference(tracee->group_leader);
235e7527 KC	325	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
	326	if (relation->invalid)
	327	continue;
2d514487 KC	328	if (relation->tracee == tracee) {
2d514487 KC	329	parent = relation->tracer;
bf06189e	330	found = true;
2d514487 KC	331	break;
2d514487 KC	332	}
235e7527	333	}
2d514487	334
bf06189e	335	if (found && (parent == NULL \|\| task_is_descendant(parent, tracer)))
2d514487 KC	336	rc = 1;
2d514487 KC	337	rcu_read_unlock();
2d514487 KC	338
	339	return rc;
	340	}
	341
	342	/**
	343	* yama_ptrace_access_check - validate PTRACE_ATTACH calls
	344	* @child: task that current task is attempting to ptrace
	345	* @mode: ptrace attach mode
	346	*
	347	* Returns 0 if following the ptrace is allowed, -ve on error.
	348	*/
b1d9e6b0	349	static int yama_ptrace_access_check(struct task_struct *child,
2d514487 KC	350	unsigned int mode)
2d514487 KC	351	{
b1d9e6b0	352	int rc = 0;
2d514487 KC	353
2d514487 KC	354	/* require ptrace target be a child of ptracer on attach */
3dfb7d8c	355	if (mode & PTRACE_MODE_ATTACH) {
389da25f KC	356	switch (ptrace_scope) {
	357	case YAMA_SCOPE_DISABLED:
	358	/* No additional restrictions. */
	359	break;
	360	case YAMA_SCOPE_RELATIONAL:
4c44aaaf	361	rcu_read_lock();
389da25f KC	362	if (!task_is_descendant(current, child) &&
389da25f KC	363	!ptracer_exception_found(current, child) &&
4c44aaaf	364	!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
389da25f	365	rc = -EPERM;
4c44aaaf	366	rcu_read_unlock();
389da25f KC	367	break;
389da25f KC	368	case YAMA_SCOPE_CAPABILITY:
4c44aaaf EB	369	rcu_read_lock();
4c44aaaf EB	370	if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
389da25f	371	rc = -EPERM;
4c44aaaf	372	rcu_read_unlock();
389da25f KC	373	break;
	374	case YAMA_SCOPE_NO_ATTACH:
	375	default:
	376	rc = -EPERM;
	377	break;
	378	}
	379	}
2d514487	380
8a56038c KC	381	if (rc && (mode & PTRACE_MODE_NOAUDIT) == 0)
8a56038c KC	382	report_access("attach", child, current);
2d514487 KC	383
	384	return rc;
	385	}
	386
9d8dad74 KC	387	/**
	388	* yama_ptrace_traceme - validate PTRACE_TRACEME calls
	389	* @parent: task that will become the ptracer of the current task
	390	*
	391	* Returns 0 if following the ptrace is allowed, -ve on error.
	392	*/
c6993e4a	393	int yama_ptrace_traceme(struct task_struct *parent)
9d8dad74	394	{
b1d9e6b0	395	int rc = 0;
9d8dad74 KC	396
	397	/* Only disallow PTRACE_TRACEME on more aggressive settings. */
	398	switch (ptrace_scope) {
	399	case YAMA_SCOPE_CAPABILITY:
eddc0a3a	400	if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE))
9d8dad74 KC	401	rc = -EPERM;
	402	break;
	403	case YAMA_SCOPE_NO_ATTACH:
	404	rc = -EPERM;
	405	break;
	406	}
	407
dca6b414 JH	408	if (rc) {
dca6b414 JH	409	task_lock(current);
8a56038c	410	report_access("traceme", current, parent);
dca6b414 JH	411	task_unlock(current);
dca6b414 JH	412	}
9d8dad74 KC	413
	414	return rc;
	415	}
	416
b1d9e6b0	417	static struct security_hook_list yama_hooks[] = {
e20b043a CS	418	LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check),
	419	LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme),
	420	LSM_HOOK_INIT(task_prctl, yama_task_prctl),
	421	LSM_HOOK_INIT(task_free, yama_task_free),
2d514487	422	};
b1d9e6b0	423
2d514487	424	#ifdef CONFIG_SYSCTL
389da25f KC	425	static int yama_dointvec_minmax(struct ctl_table *table, int write,
	426	void __user buffer, size_t lenp, loff_t *ppos)
	427	{
41a4695c	428	struct ctl_table table_copy;
389da25f KC	429
	430	if (write && !capable(CAP_SYS_PTRACE))
	431	return -EPERM;
	432
389da25f	433	/* Lock the max value if it ever gets set. */
41a4695c KC	434	table_copy = *table;
	435	if ((int )table_copy.data == (int )table_copy.extra2)
	436	table_copy.extra1 = table_copy.extra2;
389da25f	437
41a4695c	438	return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
389da25f KC	439	}
389da25f KC	440
2d514487	441	static int zero;
389da25f	442	static int max_scope = YAMA_SCOPE_NO_ATTACH;
2d514487 KC	443
	444	struct ctl_path yama_sysctl_path[] = {
	445	{ .procname = "kernel", },
	446	{ .procname = "yama", },
	447	{ }
	448	};
	449
	450	static struct ctl_table yama_sysctl_table[] = {
	451	{
	452	.procname = "ptrace_scope",
	453	.data = &ptrace_scope,
	454	.maxlen = sizeof(int),
	455	.mode = 0644,
389da25f	456	.proc_handler = yama_dointvec_minmax,
2d514487	457	.extra1 = &zero,
389da25f	458	.extra2 = &max_scope,
2d514487 KC	459	},
	460	{ }
	461	};
730daa16	462	static void __init yama_init_sysctl(void)
2d514487	463	{
2d514487 KC	464	if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
2d514487 KC	465	panic("Yama: sysctl registration failed.\n");
2d514487	466	}
730daa16 KC	467	#else
	468	static inline void yama_init_sysctl(void) { }
	469	#endif /* CONFIG_SYSCTL */
2d514487	470
730daa16 KC	471	void __init yama_add_hooks(void)
	472	{
	473	pr_info("Yama: becoming mindful.\n");
	474	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks));
	475	yama_init_sysctl();
	476	}