CRED: Fix get_task_cred() and task_state() to not resurrect dead credentials

[net-next-2.6.git] / kernel / cred.c

diff --git a/kernel/cred.c b/kernel/cred.c
index a2d5504fbcc24abb44c44a158521617933df4367..60bc8b1e32e632eb2a51b318f1ae35486d01174f 100644 (file)
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -209,6 +209,31 @@ void exit_creds(struct task_struct *tsk)
        }
 }
 
+/**
+ * get_task_cred - Get another task's objective credentials
+ * @task: The task to query
+ *
+ * Get the objective credentials of a task, pinning them so that they can't go
+ * away.  Accessing a task's credentials directly is not permitted.
+ *
+ * The caller must also make sure task doesn't get deleted, either by holding a
+ * ref on task or by holding tasklist_lock to prevent it from being unlinked.
+ */
+const struct cred *get_task_cred(struct task_struct *task)
+{
+       const struct cred *cred;
+
+       rcu_read_lock();
+
+       do {
+               cred = __task_cred((task));
+               BUG_ON(!cred);
+       } while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));
+
+       rcu_read_unlock();
+       return cred;
+}
+
 /*
  * Allocate blank credentials, such that the credentials can be filled in at a
  * later date without risk of ENOMEM.