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Date: Mon, 19 Nov 2012 15:34:59 -0800
From: Kees Cook <keescook@...omium.org>
To: linux-kernel@...r.kernel.org
Cc: James Morris <james.l.morris@...cle.com>,
Kees Cook <keescook@...omium.org>,
John Johansen <john.johansen@...onical.com>,
"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
Eric Paris <eparis@...hat.com>,
linux-security-module@...r.kernel.org
Subject: [PATCH] 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.
Cc: Sasha Levin <sasha.levin@...cle.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
security/yama/yama_lsm.c | 43 ++++++++++++++++++++++++++++++++++++-------
1 file changed, 36 insertions(+), 7 deletions(-)
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 17da6ca..1cba901 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -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 +38,27 @@ 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);
+ list_for_each_entry_rcu(relation, &ptracer_relations, node) {
+ if (relation->invalid) {
+ list_del_rcu(&relation->node);
+ kfree_rcu(relation, rcu);
+ }
+ }
+ 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
@@ -57,9 +80,12 @@ 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);
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);
@@ -70,7 +96,7 @@ static int yama_ptracer_add(struct task_struct *tracer,
list_add_rcu(&added->node, &ptracer_relations);
out:
- spin_unlock_bh(&ptracer_relations_lock);
+ spin_unlock(&ptracer_relations_lock);
return 0;
}
@@ -84,15 +110,15 @@ static void yama_ptracer_del(struct task_struct *tracer,
{
struct ptrace_relation *relation;
- spin_lock_bh(&ptracer_relations_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;
+ schedule_work(&yama_relation_work);
}
}
- spin_unlock_bh(&ptracer_relations_lock);
}
/**
@@ -219,12 +245,15 @@ 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;
--
1.7.9.5
--
Kees Cook
Chrome OS Security
--
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