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Commit 235e7527 authored by Kees Cook's avatar Kees Cook
Browse files

Yama: remove locking from delete path 



Instead of locking the list during a delete, mark entries as invalid
and trigger a workqueue to clean them up. This lets us easily handle
task_free from interrupt context.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 93b69d43

security/yama/yama_lsm.c

+42 −7
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#include <linux/ptrace.h>

#include <linux/prctl.h>

#include <linux/ratelimit.h>

#include <linux/workqueue.h>



#define YAMA_SCOPE_DISABLED	0

#define YAMA_SCOPE_RELATIONAL	1
@@ -29,6 +30,7 @@ static int ptrace_scope = YAMA_SCOPE_RELATIONAL; 
struct ptrace_relation {

	struct task_struct *tracer;

	struct task_struct *tracee;

	bool invalid;

	struct list_head node;

	struct rcu_head rcu;

};
@@ -36,6 +38,29 @@ struct ptrace_relation { 
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);



/**

 * 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
@@ -57,10 +82,13 @@ static int yama_ptracer_add(struct task_struct *tracer, 


	added->tracee = tracee;

	added->tracer = tracer;

	added->invalid = false;



	spin_lock_bh(&ptracer_relations_lock);

	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);
@@ -72,7 +100,7 @@ static int yama_ptracer_add(struct task_struct *tracer, 


out:

	rcu_read_unlock();

	spin_unlock_bh(&ptracer_relations_lock);

	spin_unlock(&ptracer_relations_lock);

	return 0;

}
@@ -85,18 +113,22 @@ static void yama_ptracer_del(struct task_struct *tracer, 
			     struct task_struct *tracee)

{

	struct ptrace_relation *relation;

	bool marked = false;



	spin_lock_bh(&ptracer_relations_lock);

	rcu_read_lock();

	list_for_each_entry_rcu(relation, &ptracer_relations, node) {

		if (relation->invalid)

			continue;

		if (relation->tracee == tracee ||

		    (tracer && relation->tracer == tracer)) {

			list_del_rcu(&relation->node);

			kfree_rcu(relation, rcu);

			relation->invalid = true;

			marked = true;

		}

	}

	rcu_read_unlock();

	spin_unlock_bh(&ptracer_relations_lock);



	if (marked)

		schedule_work(&yama_relation_work);

}



/**
@@ -223,12 +255,15 @@ static int ptracer_exception_found(struct task_struct *tracer, 
	rcu_read_lock();

	if (!thread_group_leader(tracee))

		tracee = rcu_dereference(tracee->group_leader);

	list_for_each_entry_rcu(relation, &ptracer_relations, node)

	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;