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

[Oleg Nesterov <oleg@redhat.com>]

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.