Re: [PATCH v17 08/15] seccomp: add system call filtering using BPF

[Will Drewry]

On Tue, Apr 10, 2012 at 3:00 PM, Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 9 Apr 2012 14:59:00 -0500
> Will Drewry <wad@xxxxxxxxxxxx> 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 ;)

I was wildly speculating about it, but maybe I should stop doing that.

> This is a regular old allocation of kernel memory - the thing to use
> here is GFP_KERNEL|__GFP_NOWARN.

Sounds good - I've just changed the patchset to that effect.

> (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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