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Message-Id: <20120410130017.0d20e1b2.akpm@linux-foundation.org>
Date: Tue, 10 Apr 2012 13:00:17 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Will Drewry <wad@...omium.org>
Cc: Indan Zupancic <indan@....nu>, linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org, linux-arch@...r.kernel.org,
linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de, davem@...emloft.net,
hpa@...or.com, mingo@...hat.com, oleg@...hat.com, peterz@...radead.org,
rdunlap@...otime.net, mcgrathr@...omium.org, tglx@...utronix.de,
luto@....edu, eparis@...hat.com, serge.hallyn@...onical.com,
djm@...drot.org, scarybeasts@...il.com, pmoore@...hat.com, corbet@....net,
eric.dumazet@...il.com, markus@...omium.org, coreyb@...ux.vnet.ibm.com,
keescook@...omium.org, jmorris@...ei.org
Subject: Re: [PATCH v17 08/15] seccomp: add system call filtering using BPF
On Mon, 9 Apr 2012 14:59:00 -0500
Will Drewry <wad@...omium.org> wrote:
> >> I think this gives userspace an easy way of causing page allocation
> >> failure warnings, by permitting large kmalloc() attempts. __Add
> >> __GFP_NOWARN?
> >
> > Max is 32kb. sk_attach_filter() in net/core/filter.c is worse,
> > it allocates up to 512kb before even checking the length.
> >
> > What about using GFP_USER (and adding __GFP_NOWARN to GFP_USER) instead?
>
> It looks like GFP_USER|__GFP_NOWARN would make sense here. I'll change it.
I'm not really sure why GFP_USER exists. It's very rarely used, and
most usages are probably inappropriate. To me it means "same as
GFP_HIGHUSER, only don't use highmem". That's relevant to blockdev
pagecache and nothing else as far as I can tell. And good luck working
out what the __GFP_HARDWALL does ;)
This is a regular old allocation of kernel memory - the thing to use
here is GFP_KERNEL|__GFP_NOWARN.
(I'm surprised that we didn't remove __GFP_NOWARN ages ago - warning by
default is pretty obnoxious. But the warning continues to be
occasionally useful and false positives are rare).
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