Re: [PATCH] proc: fix NULL dereference when reading /proc/<pid>/auxv

From: Leon Yu
Date: Thu Oct 20 2016 - 08:33:48 EST

On Thu, Oct 20, 2016 at 1:17 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> So here is my RFC as an alternative. Thoughts? Please note that we
> currently have only very few users of use_mm() API in the kernel
> so a risk of a regression is not really high. usb/gadget are using it
> only temporarily. The remaining is vhost which operates on a remote mm
> and I have no idea whether somebody might abuse /proc/vhost/mem or
> anything - let's add Michael to the CC list. I am pretty sure nobody
> abuse oom_reaper proc directory as this one is pretty new and such a
> usage would be pretty much undefined as the reaper unmaps the address
> space.

With this patch I cannot tell the difference between a) the thread is
exiting and b) it's a kernel thread,
besides, getting "no such process" while the kthread does exist is a
bit confusing.

IMO, reading /proc/<kthread_pid>/auxv and getting empty output are
quite straightforward,
it doesn't seem to be that "abusive".