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

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Yama Linux Security Module
 *
 * Author: Kees Cook <keescook@chromium.org>
 *
 * Copyright (C) 2010 Canonical, Ltd.
 * Copyright (C) 2011 The Chromium OS Authors.
 */

#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, TWA_RESUME) == 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
 */
static 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.
 */
static 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 (!pid_alive(child))
				rc = -EPERM;
			if (!rc && !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.
 */
static 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[] __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 *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 max_scope = YAMA_SCOPE_NO_ATTACH;

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

static int __init yama_init(void)
{
	pr_info("Yama: becoming mindful.\n");
	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama");
	yama_init_sysctl();
	return 0;
}

DEFINE_LSM(yama) = {
	.name = "yama",
	.init = yama_init,
};
Commit	Line	Data
d2912cb1	1	// SPDX-License-Identifier: GPL-2.0-only
2d514487 KC	2	/*
	3	* Yama Linux Security Module
	4	*
	5	* Author: Kees Cook <keescook@chromium.org>
	6	*
	7	* Copyright (C) 2010 Canonical, Ltd.
	8	* Copyright (C) 2011 The Chromium OS Authors.
2d514487 KC	9	*/
2d514487 KC	10
3c4ed7bd	11	#include <linux/lsm_hooks.h>
2d514487 KC	12	#include <linux/sysctl.h>
	13	#include <linux/ptrace.h>
	14	#include <linux/prctl.h>
	15	#include <linux/ratelimit.h>
235e7527	16	#include <linux/workqueue.h>
8a56038c	17	#include <linux/string_helpers.h>
dca6b414 JH	18	#include <linux/task_work.h>
	19	#include <linux/sched.h>
	20	#include <linux/spinlock.h>
2d514487	21
389da25f KC	22	#define YAMA_SCOPE_DISABLED 0
	23	#define YAMA_SCOPE_RELATIONAL 1
	24	#define YAMA_SCOPE_CAPABILITY 2
	25	#define YAMA_SCOPE_NO_ATTACH 3
	26
	27	static int ptrace_scope = YAMA_SCOPE_RELATIONAL;
2d514487 KC	28
	29	/* describe a ptrace relationship for potential exception */
	30	struct ptrace_relation {
	31	struct task_struct *tracer;
	32	struct task_struct *tracee;
235e7527	33	bool invalid;
2d514487	34	struct list_head node;
93b69d43	35	struct rcu_head rcu;
2d514487 KC	36	};
	37
	38	static LIST_HEAD(ptracer_relations);
	39	static DEFINE_SPINLOCK(ptracer_relations_lock);
	40
235e7527 KC	41	static void yama_relation_cleanup(struct work_struct *work);
	42	static DECLARE_WORK(yama_relation_work, yama_relation_cleanup);
	43
dca6b414 JH	44	struct access_report_info {
	45	struct callback_head work;
	46	const char *access;
	47	struct task_struct *target;
	48	struct task_struct *agent;
	49	};
	50
	51	static void __report_access(struct callback_head *work)
8a56038c	52	{
dca6b414 JH	53	struct access_report_info *info =
dca6b414 JH	54	container_of(work, struct access_report_info, work);
8a56038c KC	55	char target_cmd, agent_cmd;
8a56038c KC	56
dca6b414 JH	57	target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL);
dca6b414 JH	58	agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL);
8a56038c KC	59
	60	pr_notice_ratelimited(
	61	"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
dca6b414 JH	62	info->access, target_cmd, info->target->pid, agent_cmd,
dca6b414 JH	63	info->agent->pid);
8a56038c KC	64
	65	kfree(agent_cmd);
	66	kfree(target_cmd);
dca6b414 JH	67
	68	put_task_struct(info->agent);
	69	put_task_struct(info->target);
	70	kfree(info);
	71	}
	72
	73	/* defers execution because cmdline access can sleep */
	74	static void report_access(const char access, struct task_struct target,
	75	struct task_struct *agent)
	76	{
	77	struct access_report_info *info;
	78	char agent_comm[sizeof(agent->comm)];
	79
	80	assert_spin_locked(&target->alloc_lock); /* for target->comm */
	81
	82	if (current->flags & PF_KTHREAD) {
	83	/* I don't think kthreads call task_work_run() before exiting.
	84	* Imagine angry ranting about procfs here.
	85	*/
	86	pr_notice_ratelimited(
	87	"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
	88	access, target->comm, target->pid,
	89	get_task_comm(agent_comm, agent), agent->pid);
	90	return;
	91	}
	92
	93	info = kmalloc(sizeof(*info), GFP_ATOMIC);
	94	if (!info)
	95	return;
	96	init_task_work(&info->work, __report_access);
	97	get_task_struct(target);
	98	get_task_struct(agent);
	99	info->access = access;
	100	info->target = target;
	101	info->agent = agent;
91989c70	102	if (task_work_add(current, &info->work, TWA_RESUME) == 0)
dca6b414 JH	103	return; /* success */
	104
	105	WARN(1, "report_access called from exiting task");
	106	put_task_struct(target);
	107	put_task_struct(agent);
	108	kfree(info);
8a56038c KC	109	}
8a56038c KC	110
235e7527 KC	111	/**
	112	* yama_relation_cleanup - remove invalid entries from the relation list
	113	*
	114	*/
	115	static void yama_relation_cleanup(struct work_struct *work)
	116	{
	117	struct ptrace_relation *relation;
	118
	119	spin_lock(&ptracer_relations_lock);
	120	rcu_read_lock();
	121	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
	122	if (relation->invalid) {
	123	list_del_rcu(&relation->node);
	124	kfree_rcu(relation, rcu);
	125	}
	126	}
	127	rcu_read_unlock();
	128	spin_unlock(&ptracer_relations_lock);
	129	}
	130
2d514487 KC	131	/**
	132	* yama_ptracer_add - add/replace an exception for this tracer/tracee pair
	133	* @tracer: the task_struct of the process doing the ptrace
	134	* @tracee: the task_struct of the process to be ptraced
	135	*
	136	* Each tracee can have, at most, one tracer registered. Each time this
	137	* is called, the prior registered tracer will be replaced for the tracee.
	138	*
	139	* Returns 0 if relationship was added, -ve on error.
	140	*/
	141	static int yama_ptracer_add(struct task_struct *tracer,
	142	struct task_struct *tracee)
	143	{
93b69d43	144	struct ptrace_relation relation, added;
2d514487 KC	145
	146	added = kmalloc(sizeof(*added), GFP_KERNEL);
	147	if (!added)
	148	return -ENOMEM;
	149
93b69d43 KC	150	added->tracee = tracee;
93b69d43 KC	151	added->tracer = tracer;
235e7527	152	added->invalid = false;
93b69d43	153
235e7527	154	spin_lock(&ptracer_relations_lock);
93b69d43 KC	155	rcu_read_lock();
93b69d43 KC	156	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
235e7527 KC	157	if (relation->invalid)
235e7527 KC	158	continue;
93b69d43 KC	159	if (relation->tracee == tracee) {
	160	list_replace_rcu(&relation->node, &added->node);
	161	kfree_rcu(relation, rcu);
	162	goto out;
2d514487	163	}
2d514487	164	}
2d514487	165
93b69d43	166	list_add_rcu(&added->node, &ptracer_relations);
2d514487	167
93b69d43 KC	168	out:
93b69d43 KC	169	rcu_read_unlock();
235e7527	170	spin_unlock(&ptracer_relations_lock);
93b69d43	171	return 0;
2d514487 KC	172	}
	173
	174	/**
	175	* yama_ptracer_del - remove exceptions related to the given tasks
	176	* @tracer: remove any relation where tracer task matches
	177	* @tracee: remove any relation where tracee task matches
	178	*/
	179	static void yama_ptracer_del(struct task_struct *tracer,
	180	struct task_struct *tracee)
	181	{
93b69d43	182	struct ptrace_relation *relation;
235e7527	183	bool marked = false;
2d514487	184
93b69d43 KC	185	rcu_read_lock();
93b69d43 KC	186	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
235e7527 KC	187	if (relation->invalid)
235e7527 KC	188	continue;
2d514487	189	if (relation->tracee == tracee \|\|
bf06189e	190	(tracer && relation->tracer == tracer)) {
235e7527 KC	191	relation->invalid = true;
235e7527 KC	192	marked = true;
2d514487	193	}
93b69d43 KC	194	}
93b69d43 KC	195	rcu_read_unlock();
235e7527 KC	196
	197	if (marked)
	198	schedule_work(&yama_relation_work);
2d514487 KC	199	}
	200
	201	/**
	202	* yama_task_free - check for task_pid to remove from exception list
	203	* @task: task being removed
	204	*/
1aa176ef	205	static void yama_task_free(struct task_struct *task)
2d514487 KC	206	{
	207	yama_ptracer_del(task, task);
	208	}
	209
	210	/**
	211	* yama_task_prctl - check for Yama-specific prctl operations
	212	* @option: operation
	213	* @arg2: argument
	214	* @arg3: argument
	215	* @arg4: argument
	216	* @arg5: argument
	217	*
	218	* Return 0 on success, -ve on error. -ENOSYS is returned when Yama
	219	* does not handle the given option.
	220	*/
1aa176ef	221	static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
2d514487 KC	222	unsigned long arg4, unsigned long arg5)
2d514487 KC	223	{
b1d9e6b0	224	int rc = -ENOSYS;
2d514487 KC	225	struct task_struct *myself = current;
2d514487 KC	226
2d514487 KC	227	switch (option) {
	228	case PR_SET_PTRACER:
	229	/* Since a thread can call prctl(), find the group leader
	230	* before calling _add() or _del() on it, since we want
	231	* process-level granularity of control. The tracer group
	232	* leader checking is handled later when walking the ancestry
	233	* at the time of PTRACE_ATTACH check.
	234	*/
	235	rcu_read_lock();
	236	if (!thread_group_leader(myself))
	237	myself = rcu_dereference(myself->group_leader);
	238	get_task_struct(myself);
	239	rcu_read_unlock();
	240
	241	if (arg2 == 0) {
	242	yama_ptracer_del(NULL, myself);
	243	rc = 0;
2e4930eb	244	} else if (arg2 == PR_SET_PTRACER_ANY \|\| (int)arg2 == -1) {
bf06189e	245	rc = yama_ptracer_add(NULL, myself);
2d514487 KC	246	} else {
	247	struct task_struct *tracer;
	248
2ee08260 MR	249	tracer = find_get_task_by_vpid(arg2);
2ee08260 MR	250	if (!tracer) {
2d514487	251	rc = -EINVAL;
2ee08260	252	} else {
2d514487 KC	253	rc = yama_ptracer_add(tracer, myself);
	254	put_task_struct(tracer);
	255	}
	256	}
	257
	258	put_task_struct(myself);
	259	break;
	260	}
	261
	262	return rc;
	263	}
	264
	265	/**
	266	* task_is_descendant - walk up a process family tree looking for a match
	267	* @parent: the process to compare against while walking up from child
	268	* @child: the process to start from while looking upwards for parent
	269	*
	270	* Returns 1 if child is a descendant of parent, 0 if not.
	271	*/
	272	static int task_is_descendant(struct task_struct *parent,
	273	struct task_struct *child)
	274	{
	275	int rc = 0;
	276	struct task_struct *walker = child;
	277
	278	if (!parent \|\| !child)
	279	return 0;
	280
	281	rcu_read_lock();
	282	if (!thread_group_leader(parent))
	283	parent = rcu_dereference(parent->group_leader);
	284	while (walker->pid > 0) {
	285	if (!thread_group_leader(walker))
	286	walker = rcu_dereference(walker->group_leader);
	287	if (walker == parent) {
	288	rc = 1;
	289	break;
	290	}
	291	walker = rcu_dereference(walker->real_parent);
	292	}
	293	rcu_read_unlock();
	294
	295	return rc;
	296	}
	297
	298	/**
	299	* ptracer_exception_found - tracer registered as exception for this tracee
	300	* @tracer: the task_struct of the process attempting ptrace
	301	* @tracee: the task_struct of the process to be ptraced
	302	*
50523a29	303	* Returns 1 if tracer has a ptracer exception ancestor for tracee.
2d514487 KC	304	*/
	305	static int ptracer_exception_found(struct task_struct *tracer,
	306	struct task_struct *tracee)
	307	{
	308	int rc = 0;
	309	struct ptrace_relation *relation;
	310	struct task_struct *parent = NULL;
bf06189e	311	bool found = false;
2d514487	312
2d514487	313	rcu_read_lock();
50523a29 JS	314
	315	/*
	316	* If there's already an active tracing relationship, then make an
	317	* exception for the sake of other accesses, like process_vm_rw().
	318	*/
	319	parent = ptrace_parent(tracee);
	320	if (parent != NULL && same_thread_group(parent, tracer)) {
	321	rc = 1;
	322	goto unlock;
	323	}
	324
	325	/* Look for a PR_SET_PTRACER relationship. */
2d514487 KC	326	if (!thread_group_leader(tracee))
2d514487 KC	327	tracee = rcu_dereference(tracee->group_leader);
235e7527 KC	328	list_for_each_entry_rcu(relation, &ptracer_relations, node) {
	329	if (relation->invalid)
	330	continue;
2d514487 KC	331	if (relation->tracee == tracee) {
2d514487 KC	332	parent = relation->tracer;
bf06189e	333	found = true;
2d514487 KC	334	break;
2d514487 KC	335	}
235e7527	336	}
2d514487	337
bf06189e	338	if (found && (parent == NULL \|\| task_is_descendant(parent, tracer)))
2d514487	339	rc = 1;
50523a29 JS	340
50523a29 JS	341	unlock:
2d514487	342	rcu_read_unlock();
2d514487 KC	343
	344	return rc;
	345	}
	346
	347	/**
	348	* yama_ptrace_access_check - validate PTRACE_ATTACH calls
	349	* @child: task that current task is attempting to ptrace
	350	* @mode: ptrace attach mode
	351	*
	352	* Returns 0 if following the ptrace is allowed, -ve on error.
	353	*/
b1d9e6b0	354	static int yama_ptrace_access_check(struct task_struct *child,
2d514487 KC	355	unsigned int mode)
2d514487 KC	356	{
b1d9e6b0	357	int rc = 0;
2d514487 KC	358
2d514487 KC	359	/* require ptrace target be a child of ptracer on attach */
3dfb7d8c	360	if (mode & PTRACE_MODE_ATTACH) {
389da25f KC	361	switch (ptrace_scope) {
	362	case YAMA_SCOPE_DISABLED:
	363	/* No additional restrictions. */
	364	break;
	365	case YAMA_SCOPE_RELATIONAL:
4c44aaaf	366	rcu_read_lock();
9474f4e7 KC	367	if (!pid_alive(child))
	368	rc = -EPERM;
	369	if (!rc && !task_is_descendant(current, child) &&
389da25f	370	!ptracer_exception_found(current, child) &&
4c44aaaf	371	!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
389da25f	372	rc = -EPERM;
4c44aaaf	373	rcu_read_unlock();
389da25f KC	374	break;
389da25f KC	375	case YAMA_SCOPE_CAPABILITY:
4c44aaaf EB	376	rcu_read_lock();
4c44aaaf EB	377	if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
389da25f	378	rc = -EPERM;
4c44aaaf	379	rcu_read_unlock();
389da25f KC	380	break;
	381	case YAMA_SCOPE_NO_ATTACH:
	382	default:
	383	rc = -EPERM;
	384	break;
	385	}
	386	}
2d514487	387
8a56038c KC	388	if (rc && (mode & PTRACE_MODE_NOAUDIT) == 0)
8a56038c KC	389	report_access("attach", child, current);
2d514487 KC	390
	391	return rc;
	392	}
	393
9d8dad74 KC	394	/**
	395	* yama_ptrace_traceme - validate PTRACE_TRACEME calls
	396	* @parent: task that will become the ptracer of the current task
	397	*
	398	* Returns 0 if following the ptrace is allowed, -ve on error.
	399	*/
1aa176ef	400	static int yama_ptrace_traceme(struct task_struct *parent)
9d8dad74	401	{
b1d9e6b0	402	int rc = 0;
9d8dad74 KC	403
	404	/* Only disallow PTRACE_TRACEME on more aggressive settings. */
	405	switch (ptrace_scope) {
	406	case YAMA_SCOPE_CAPABILITY:
eddc0a3a	407	if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE))
9d8dad74 KC	408	rc = -EPERM;
	409	break;
	410	case YAMA_SCOPE_NO_ATTACH:
	411	rc = -EPERM;
	412	break;
	413	}
	414
dca6b414 JH	415	if (rc) {
dca6b414 JH	416	task_lock(current);
8a56038c	417	report_access("traceme", current, parent);
dca6b414 JH	418	task_unlock(current);
dca6b414 JH	419	}
9d8dad74 KC	420
	421	return rc;
	422	}
	423
f22f9aaf	424	static struct security_hook_list yama_hooks[] __ro_after_init = {
e20b043a CS	425	LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check),
	426	LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme),
	427	LSM_HOOK_INIT(task_prctl, yama_task_prctl),
	428	LSM_HOOK_INIT(task_free, yama_task_free),
2d514487	429	};
b1d9e6b0	430
2d514487	431	#ifdef CONFIG_SYSCTL
389da25f	432	static int yama_dointvec_minmax(struct ctl_table *table, int write,
32927393	433	void buffer, size_t lenp, loff_t *ppos)
389da25f	434	{
41a4695c	435	struct ctl_table table_copy;
389da25f KC	436
	437	if (write && !capable(CAP_SYS_PTRACE))
	438	return -EPERM;
	439
389da25f	440	/* Lock the max value if it ever gets set. */
41a4695c KC	441	table_copy = *table;
	442	if ((int )table_copy.data == (int )table_copy.extra2)
	443	table_copy.extra1 = table_copy.extra2;
389da25f	444
41a4695c	445	return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
389da25f KC	446	}
389da25f KC	447
389da25f	448	static int max_scope = YAMA_SCOPE_NO_ATTACH;
2d514487	449
2d514487 KC	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,
eec4844f	457	.extra1 = SYSCTL_ZERO,
389da25f	458	.extra2 = &max_scope,
2d514487 KC	459	},
	460	{ }
	461	};
730daa16	462	static void __init yama_init_sysctl(void)
2d514487	463	{
98cfeb8d	464	if (!register_sysctl("kernel/yama", yama_sysctl_table))
2d514487	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
d6aed64b	471	static int __init yama_init(void)
730daa16 KC	472	{
730daa16 KC	473	pr_info("Yama: becoming mindful.\n");
d69dece5	474	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama");
730daa16	475	yama_init_sysctl();
d6aed64b	476	return 0;
730daa16	477	}
d6aed64b KC	478
	479	DEFINE_LSM(yama) = {
	480	.name = "yama",
	481	.init = yama_init,
	482	};