Yama: add RCU to drop read locking

[cascardo/linux.git] / security / yama / yama_lsm.c

diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index b4c2984..70cd85e 100644 (file)
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -30,6 +30,7 @@ struct ptrace_relation {
        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 DEFINE_SPINLOCK(ptracer_relations_lock);
 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;
 
-       spin_unlock_bh(&ptracer_relations_lock);
-       if (added != relation)
-               kfree(added);
+       list_add_rcu(&added->node, &ptracer_relations);
 
-       return rc;
+out:
+       rcu_read_unlock();
+       spin_unlock_bh(&ptracer_relations_lock);
+       return 0;
 }
 
 /**
@@ -84,15 +84,18 @@ static int yama_ptracer_add(struct task_struct *tracer,
 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 @@ static int ptracer_exception_found(struct task_struct *tracer,
        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 @@ static int ptracer_exception_found(struct task_struct *tracer,
        if (found && (parent == NULL || task_is_descendant(parent, tracer)))
                rc = 1;
        rcu_read_unlock();
-       spin_unlock_bh(&ptracer_relations_lock);
 
        return rc;
 }