Re: [netfilter-core] kernel panic: Out of memory and no killable processes... (2)

[Michal Hocko]

On Tue 30-01-18 10:02:34, Dmitry Vyukov wrote:
> On Tue, Jan 30, 2018 at 9:28 AM, Kirill A. Shutemov
> <kirill@xxxxxxxxxxxxx> wrote:
> > On Tue, Jan 30, 2018 at 09:11:27AM +0100, Florian Westphal wrote:
> >> Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> >> > On Mon 29-01-18 23:35:22, Florian Westphal wrote:
> >> > > Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
> >> > [...]
> >> > > > I hate what I'm saying, but I guess we need some tunable here.
> >> > > > Not sure what exactly.
> >> > >
> >> > > Would memcg help?
> >> >
> >> > That really depends. I would have to check whether vmalloc path obeys
> >> > __GFP_ACCOUNT (I suspect it does except for page tables allocations but
> >> > that shouldn't be a big deal). But then the other potential problem is
> >> > the life time of the xt_table_info (or other potentially large) data
> >> > structures. Are they bound to any process life time.
> >>
> >> No.
> >
> > Well, IIUC they bound to net namespace life time, so killing all
> > proccesses in the namespace would help to get memory back. :)
> 
> ... unless the namespace is mounted into file system.
> 
> Let's start with NOWARN as that's what kernel generally uses for
> allocations with user-controllable size. ENOMEM is roughly as
> informative as the WARNING message in this case.

You want __GFP_NORETRY but that is not _fully_ supported by kvmalloc
right now. More specifically kvmalloc doesn't guanratee that the request
will not trigger the OOM killer (like regular __GFP_NORETRY). This is
because of internal vmalloc restrictions. If you are however OK to
simply bail out in most cases then __GFP_NORETRY should work reasonably
fine.

> I think we also need to consider setting up memory cgroup for
> syzkaller test processes (we do RLIMIT_AS, but that's weak).

Well, this is not about syzkaller, it merely pointed out a potential
DoS... And that has to be addressed somehow.

-- 
Michal Hocko
SUSE Labs