lkml.org 
[lkml]   [2011]   [May]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 10/11] ptrace: move JOBCTL_TRAPPING wait to wait(2) and ptrace_check_attach()
On 05/11, Oleg Nesterov wrote:
>
> You know, I'd wish I could find the serious bugs in this patch. The
> code becomes really hairy. -EAGAIN in do_wait() doesn't make it more
> simple ;)

Mwahaha! I seem to see the bug ;)

bool ptrace_wait_trapping(struct task_struct *child)
__releases(&child->sighand->siglock)
__releases(&tasklist_lock)
{
if (likely(!(child->jobctl & JOBCTL_TRAPPING)))
return false;
spin_unlock_irq(&child->sighand->siglock);
get_task_struct(child);
read_unlock(&tasklist_lock);

--> WINDOW

wait_event(current->signal->wait_chldexit,
!(child->jobctl & JOBCTL_TRAPPING));
put_task_struct(child);
return true;
}
When the caller is do_wait(), we can't assume we are the tracer when
we drop tasklist. Original tracer can detach, then another unrelated
process can attach again and provoke JOBCTL_TRAPPING. wait_event()
can hang forever.

Unfortunately, this is easy to fix :/

Oleg.



\
 
 \ /
  Last update: 2011-05-11 19:05    [from the cache]
©2003-2011 Jasper Spaans