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

[Michal Hocko]

On Wed 19-10-16 15:20:15, Al Viro wrote:
> On Wed, Oct 19, 2016 at 09:59:40PM +0800, Leon Yu wrote:
> > Reading auxv of any kernel thread results in NULL pointer dereferencing in
> > auxv_read() where mm can be NULL or even error code. Fix that by testing mm
> > with IS_ERR_OR_NULL() helper. This is also the original behavior changed by
> > recent commit c5317167854e ("proc: switch auxv to use of __mem_open()").
> 
> What the...  How can it be ERR_PTR(...) after it has passed __mem_open()?
> I agree that we ought to check for NULL mm (the only question is whether it's
> best done by failing open() or by treating the file as empty), but this

I believe failing open is a better approach because even if a particualr
thread has hijacked a mm via use_mm then the output we will provide is
misleading at best. See my suggestion
http://lkml.kernel.org/r/20161019141346.GJ7517@xxxxxxxxxxxxxx
-- 
Michal Hocko
SUSE Labs