• Oleg Nesterov's avatar
    cred: remove task_is_dead() from __task_cred() validation · 43e13cc1
    Oleg Nesterov authored
    Commit 8f92054e ("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: default avatarOleg Nesterov <oleg@redhat.com>
    Reviewed-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
    Acked-by: default avatarDavid 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: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    43e13cc1
cred.h 11.7 KB