linux-kernel - Re: suppress page allocation failure warnings from sys

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Message-Id: <20120328192804.7326bce9.akpm@linux-foundation.org>
Date:	Wed, 28 Mar 2012 19:28:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>
Cc:	Joe Perches <joe@...ches.com>, Dave Chinner <david@...morbit.com>,
	viro@...iv.linux.org.uk,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: suppress page allocation failure warnings from sys_listxattr

On Wed, 28 Mar 2012 22:08:20 -0400 Dave Jones <davej@...hat.com> 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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