Re: [PATCH] proc: Disable /proc/$pid/wchan

[Andrew Morton]

On Thu, 23 Sep 2021 16:31:05 -0700 Kees Cook <keescook@xxxxxxxxxxxx> wrote:

> The /proc/$pid/wchan file has been broken by default on x86_64 for 4
> years now[1].

[1] is hard to decrypt.  I think it would be better if this changelog
were to describe the problem directly, completely and succinctly?

> As this remains a potential leak of either kernel
> addresses (when symbolization fails) or limited observation of kernel
> function progress, just remove the contents for good.
> 
> Unconditionally set the contents to "0" and also mark the wchan
> field in /proc/$pid/stat with 0.
> 
> This leaves kernel/sched/fair.c as the only user of get_wchan(). But
> again, since this was broken for 4 years, was this profiling logic
> actually doing anything useful?

Agree that returning a hard-wired "0\n" is the way to go.