cred: remove task_is_dead() from __task_cred() validation
Commit 8f92054e7ca1 ("CRED: Fix __task_cred()'s lockdep check and banner
comment"):
add the following validation condition:
task->exit_state >= 0
to permit the access if the target task is dead and therefore
unable to change its own credentials.
OK, but afaics currently this can only help wait_task_zombie() which calls
__task_cred() without rcu lock.
Remove this validation and change wait_task_zombie() to use task_uid()
instead. This means we do rcu_read_lock() only to shut up the lockdep,
but we already do the same in, say, wait_task_stopped().
task_is_dead() should die, task->exit_state != 0 means that this task has
passed exit_notify(), only do_wait-like code paths should use this.
Unfortunately, we can't kill task_is_dead() right now, it has already
acquired buggy users in drivers/staging. The fix already exists.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 917dc5a..ebbed2c 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -277,17 +277,13 @@
* @task: The task to query
*
* Access the objective credentials of a task. The caller must hold the RCU
- * readlock or the task must be dead and unable to change its own credentials.
+ * readlock.
*
* The result of this function should not be passed directly to get_cred();
* rather get_task_cred() should be used instead.
*/
-#define __task_cred(task) \
- ({ \
- const struct task_struct *__t = (task); \
- rcu_dereference_check(__t->real_cred, \
- task_is_dead(__t)); \
- })
+#define __task_cred(task) \
+ rcu_dereference((task)->real_cred)
/**
* get_current_cred - Get the current task's subjective credentials