linux-kernel - Re: [PATCH 03/10] ptrace: implement PTRACE

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Message-ID: <20110520090718.GC31426@htj.dyndns.org>
Date:	Fri, 20 May 2011 11:07:18 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Pedro Alves <pedro@...esourcery.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>, oleg@...hat.com,
	jan.kratochvil@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	indan@....nu, bdonlan@...il.com
Subject: Re: [PATCH 03/10] ptrace: implement PTRACE_SEIZE

Hello, Pedro.

On Fri, May 20, 2011 at 12:00:17AM +0100, Pedro Alves wrote:
> > > UUIC, that opens a race where between SEIZEing and
> > > SETOPTIONS(O_TRACE FORK|VFORK|EXEC...), the tracee can
> > > fork/vfork/clone/exec, without the tracer getting the
> > > nice corresponding PTRACE_EVENT_ events.

Does it matter?  The order of execution isn't even well defined
without synchronization border.  If you want full synchronization, you
can INTERRUPT tracee.

>  SEIZE,execvd,INTERRUPT (SETOPTS on interrupt)
> 
> will make the tracer see a SIGTRAP that 
> 
>  execvd,SEIZE,INTERRUPT
> 
> nor
> 
>  SEIZE,SETOPTS,execvd (SETOPTS on interrupt)
> 
> would cause, isn't it?

Yes, SIGTRAP on exec(2) is nasty but also is scheduled to be removed
if SEIZED.

> Now, if it were possible for the tracer to set the
> default OPTS _before_ PTRACE_ATTACH/PTRACE_SEIZE...

I don't see why that would be necessary.

Thanks.

-- 
tejun
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