lkml.org 
[lkml]   [2016]   [Sep]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach
On Thu, Sep 01, 2016 at 06:46:13PM +0200, Oleg Nesterov wrote:
> On 09/01, Ales Novak wrote:
> >
> > On ptrace_detach(), the TIF_SYSCALL_TRACE in thread->flags of the tracee
> > is not cleared up. This results in the tracehook_report_syscall_* being
> > called (though there's no longer a tracer listening to that) upon its
> > further syscalls.
> >
> > Example scenario - attach "strace" to a running process and kill it (the
> > strace) with SIGKILL. You'll see that the syscall trace hooks are still
> > being called.
>
> We do not really care, if the tracer dies the tracee can be in the
> inconsistent state anyway.
>
> > --- a/kernel/ptrace.c
> > +++ b/kernel/ptrace.c
> > @@ -85,6 +85,7 @@ void __ptrace_unlink(struct task_struct *child)
> > task_clear_jobctl_pending(child, JOBCTL_TRAP_MASK);
> > task_clear_jobctl_trapping(child);
> >
> > + clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
>
> OK, probably this change makes sense anyway, but then you should
> remove another clear_tsk_thread_flag(TIF_SYSCALL_TRACE) in ptrace_detach?

You're right, sorry for not noticing that. Also my changelog was
misleading, I've tried to fix that.

>
> And I'd suggest to move this clear_tsk_thread_flag() up, before
> spin_lock(siglock). Otherwise it looks as if we should clear this flag
> with ->siglock held.

Good point also.

>
> Oleg.
>

--
Ales Novak
SUSE L3
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2016-09-17 09:58    [W:2.240 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site