Hi Again,
> Or the child can check getppid() == saved_parent_pid after PTRACE_TRACEME.
In fact that's what I did when I tested the new option - the child ran:
volatile long ready = 0;
int saved_parent_pid = getpid();
if(!(son = fork())
{
while(!ready)
{
sched_yield();
if(getppid() != saved_parent_pid)
exit(1);
}
execve(...);
}
ptrace(PTRACE_ATTACH, son, 0, 0);
waitpid(son, ...);
ptrace(PTRACE_SETOPTIONS, son, 0, PTRACE_P_TRACEFORK|PTRACE_O_EXITKILL);
ptrace(PTRACE_POKEDATA, son, &ready, 1);
/* continue tracing */
I also checked that PTRACE_O_EXITKILL is inherited to grandchildren.
Yes, I may also use PTRACE_SEIZE, but since it is not yet documented,
I will need to read the kernel code more to make extra sure it has no
unwanted side effects.
Best Regards,
Amnon.
Oleg Nesterov wrote:
>
> Hi Amnon,
>
> On 11/08, Amnon Shiloh wrote:
> >
> > Thanks for the patch, I tried it and it works nicely!
>
> OK, thanks. I'll wait for other comments a bit and then send
> the patch to Andrew.
>
> > Also, I just noticed that this new option (PTRACE_O_EXITKILL) is not
> > safe with ptrace(PTRACE_TRACEME)+execve, because the parent may die
> > before even having a chance to set PTRACE_O_EXITKILL!
>
> Not safe? I guess you meant that PTRACE_O_EXITKILL can't prevent
> this race? Yes sure. Or the parent can die before it does
> PTRACE_O_EXITKILL.
>
> > However, that's easy to fix by using PTRACE_ATTACH instead.
>
> Or the child can check getppid() == saved_parent_pid after PTRACE_TRACEME.
>
> But if you switch to PTRACE_ATTACH, I'd suggest to use PTRACE_SEIZE.
> Note that, in particular, this allows you to specify the options at
> attach.
>
> As for PF_NO_SIGSTOP, I'll write another email.
>
> Oleg.
>
>
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