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

[Michal Hocko]

On Wed 19-10-16 18:44:29, Oleg Nesterov wrote:
> On 10/19, Michal Hocko wrote:
> >
> > On Wed 19-10-16 18:12:08, Oleg Nesterov wrote:
> > > On 10/19, Michal Hocko wrote:
> > > >
> > > > Why would we even want to open that file if there is no mm struct?
> > >
> > > Agreed this is strange, but I am not sure we can change this old
> > > behaviour. Say, cat /proc/$pid-of-kthread/mem doesn't fail, it shows
> > > the "empty mm".
> >
> > What kind of application would break?
> 
> I have no idea, probably nobody will ever notice this change, just
> I am always nervous when it comes to user-visible changes.
> 
> But why do we want this change? Not that I am going to argue if you
> submit a patch, but personally I see no real point.

I find it much easier to not allow open than a) have a weird side
effects like seeing a hijacked mm and b) risk that similar NULL ptr will
repeat again because all the code paths have to check for it explicitly.
-- 
Michal Hocko
SUSE Labs