Re: [PATCH 1/1] ptrace: Get tracer PID without reliance on the proc FS

[Oleg Nesterov <oleg@redhat.com>]

Forgot to ask...

Do you really want the tracer's pid or can PTRACE_TRACER/whatever
simply return the !!current->ptrace boolean? The changelog should
probably explain this too.

On 09/06, Oleg Nesterov wrote:
>
> Add cc's. Perhaps someone else can ack/nack the intent...
>
> This (trivial) patch is obviously buggy, but fixable. I won't argue
> if it can help userspace.
>
> On 09/05, Roman Kisel wrote:
> >
> > For debugging, it might be useful to run the debug trap
> > instruction to break into the debugger. To detect the debugger
> > presence, the kernel provides the `/proc/self/status` pseudo-file
> > that needs to be searched for the "TracerPid:" string.
> >
> > Provide a prctl command that returns the PID of the tracer if any.
>
> prctl?
>
> > That allows for much simpler logic in the user land, and makes it
> > possible to detect tracer presence even if PROC_FS is not enabled.
>
> You should probably move the links from 0/1 to the changelog to make
> it more convincing.
>
> > +	if (request == PTRACE_TRACER) {
> > +		rcu_read_lock();
> > +		tracer = ptrace_parent(current);
> > +		ret = tracer ? task_pid_nr_ns(tracer,
> > +					task_active_pid_ns(current->parent)) : -ESRCH;
>
> The namespace is wrong, we need task_active_pid_ns(current). So this
> code should simply do task_tgid_vnr(tracer) like sys_getppid() does.
> And to me it would be better to return 0 if !current->ptrace.
>
> > +		rcu_read_unlock();
> > +		goto out;
>
> Wrong, this code runs after "child = find_get_task_by_vpid(pid);" above.
>
> And why? perhaps the intent was to check if this child is traced, not
> current?
>
> Oleg.
>