Commit 8f92054e7c ("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>
43e13cc107