Yama: add RCU to drop read locking
Stop using spinlocks in the read path. Add RCU list to handle the readers.
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Acked-by: John Johansen <john.johansen@canonical.com>
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index b4c2984..70cd85e 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -30,6 +30,7 @@
struct task_struct *tracer;
struct task_struct *tracee;
struct list_head node;
+ struct rcu_head rcu;
};
static LIST_HEAD(ptracer_relations);
@@ -48,32 +49,31 @@
static int yama_ptracer_add(struct task_struct *tracer,
struct task_struct *tracee)
{
- int rc = 0;
- struct ptrace_relation *added;
- struct ptrace_relation *entry, *relation = NULL;
+ struct ptrace_relation *relation, *added;
added = kmalloc(sizeof(*added), GFP_KERNEL);
if (!added)
return -ENOMEM;
+ added->tracee = tracee;
+ added->tracer = tracer;
+
spin_lock_bh(&ptracer_relations_lock);
- list_for_each_entry(entry, &ptracer_relations, node)
- if (entry->tracee == tracee) {
- relation = entry;
- break;
+ rcu_read_lock();
+ list_for_each_entry_rcu(relation, &ptracer_relations, node) {
+ if (relation->tracee == tracee) {
+ list_replace_rcu(&relation->node, &added->node);
+ kfree_rcu(relation, rcu);
+ goto out;
}
- if (!relation) {
- relation = added;
- relation->tracee = tracee;
- list_add(&relation->node, &ptracer_relations);
}
- relation->tracer = tracer;
+ list_add_rcu(&added->node, &ptracer_relations);
+
+out:
+ rcu_read_unlock();
spin_unlock_bh(&ptracer_relations_lock);
- if (added != relation)
- kfree(added);
-
- return rc;
+ return 0;
}
/**
@@ -84,15 +84,18 @@
static void yama_ptracer_del(struct task_struct *tracer,
struct task_struct *tracee)
{
- struct ptrace_relation *relation, *safe;
+ struct ptrace_relation *relation;
spin_lock_bh(&ptracer_relations_lock);
- list_for_each_entry_safe(relation, safe, &ptracer_relations, node)
+ rcu_read_lock();
+ list_for_each_entry_rcu(relation, &ptracer_relations, node) {
if (relation->tracee == tracee ||
(tracer && relation->tracer == tracer)) {
- list_del(&relation->node);
- kfree(relation);
+ list_del_rcu(&relation->node);
+ kfree_rcu(relation, rcu);
}
+ }
+ rcu_read_unlock();
spin_unlock_bh(&ptracer_relations_lock);
}
@@ -217,11 +220,10 @@
struct task_struct *parent = NULL;
bool found = false;
- spin_lock_bh(&ptracer_relations_lock);
rcu_read_lock();
if (!thread_group_leader(tracee))
tracee = rcu_dereference(tracee->group_leader);
- list_for_each_entry(relation, &ptracer_relations, node)
+ list_for_each_entry_rcu(relation, &ptracer_relations, node)
if (relation->tracee == tracee) {
parent = relation->tracer;
found = true;
@@ -231,7 +233,6 @@
if (found && (parent == NULL || task_is_descendant(parent, tracer)))
rc = 1;
rcu_read_unlock();
- spin_unlock_bh(&ptracer_relations_lock);
return rc;
}