Re: [PATCH 1/1] creds: kill __task_cred()->task_is_dead() validation

[David Howells <dhowells@redhat.com>]

Oleg Nesterov <oleg@redhat.com> wrote:

> commit 8f92054e:
> 
>     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
> found the bugy users in drivers/staging/, the fix already exists.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: David Howells <dhowells@redhat.com>