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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: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook 2012-11-19 15:21:26 -08:00
parent 93b69d437e
commit 235e752789
1 changed files with 42 additions and 7 deletions
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49
security/yama/yama_lsm.c
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@ -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;