Re: suppress page allocation failure warnings from sys_listxattr

From: Andrew Morton
Date: Wed Mar 28 2012 - 22:24:19 EST

On Wed, 28 Mar 2012 22:08:20 -0400 Dave Jones <davej@xxxxxxxxxx> wrote:

> On Wed, Mar 28, 2012 at 07:02:11PM -0700, Andrew Morton wrote:
> > > Also, what happens if something allocates
> > > and sits on a bunch of vmalloc'd memory ? would we start seeing oom kills ?
> >
> > vmalloc() would fail.
> Ok, that's a pretty boring failure mode, so not a big deal probably.
> > > (thinking of the context of my fuzzing tool where a bunch of instances could
> > > feasibly call these syscalls and not sit on huge amounts per thread, but
> > > collectively... I'm wondering if it could be provoked into killing
> > > processes I don't own)
> >
> > umm, if you wanted to deliberately trigger a vmalloc() failure then I
> > guess a good approach would be to locate a vmalloc() site which can
> > persist beyond the syscall (modprobe is a good one!) then exercise it
> > in a way so that there are no N-byte holes left in the arena, then
> > trigger an N-byte vmalloc().
> Well modprobe is root-only, so that's not so bad.

Even if it's root-only, we can still end up with a toasted machine.
Accidentally toasted, not deliberately.

> But it looks like
> key_add (see other thread from this evening) and probably others can be
> called as a user and gobble up vmalloc space. omnomnom.

hm, the keys code appears to prevent the user from reserving more than
20000 bytes of memory total (key_payload_reserve()), so it doesn't look
very useful for screwing up vmalloc().
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