Re: [PATCH 2/4] ptrace: ensure arch_ptrace/ptrace_request can neverrace with SIGKILL

[Linus Torvalds]

On Sun, Jan 20, 2013 at 11:25 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> +
> +static void ptrace_unfreeze_traced(struct task_struct *task)
> +{
> +       if (task->state != __TASK_TRACED)
> +               return;
> +
> +       if (WARN_ON(!task->ptrace || task->parent != current))
> +               return;

This WARN_ON() is bogus.

Because you added the warning, you then need to make the callers check
for the whole PTRACE_UNATTACH.

So I think you should just remove the WARN_ON(), and then just call
ptrace_unfreeze_traced() unconditionally after you've successfully
done a ptrace_check_attach(). Just to keep the code simpler.

Also, in your corrected version, you had

+               if (!wait_task_inactive(child, __TASK_TRACED)) {
+                       /* This can only happen if may_ptrace_stop() fails */
+                       WARN_ON(child->state == __TASK_TRACED);
+                       ret = -ESRCH;

where I actually think that the comment is not really helpful. It
doesn't really explain what he child can do to get to ptrace_stop() in
the first place, and what that does to the child state...

               Linus
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