linux-kernel - Re: [PATCH RFC v2 net-next 08/16] bpf: add hashtable type of BPF maps

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Date:	Wed, 23 Jul 2014 14:42:01 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v2 net-next 08/16] bpf: add hashtable type of BPF maps

On Wed, Jul 23, 2014 at 1:33 PM, Kees Cook <keescook@...omium.org> wrote:
>>
>>>> +       htab->slab_name = kasprintf(GFP_USER, "bpf_htab_%p", htab);
>>>
>>> This leaks a kernel heap memory pointer to userspace. If a unique name
>>> needed, I think map_id should be used instead.
>>
>> it leaks, how? slabinfo is only available to root.
>> The same code exists in conntrack:
>> net/netfilter/nf_conntrack_core.c:1767
>
> Right, in extreme cases, there are system configurations where leaking
> addresses even to root can be considered a bug. There are a lot of
> these situations in the kernel still, that's true. However, if we can
> at all avoid it, I'd really like to avoid adding new ones. Nearly all
> the cases of using a memory pointer is for uniqueness concerns, but I
> think can already get that from the map_id.

ok. fair enough. I think slab name doesn't have to be unique anymore.
It's used to be a requirement in older kernels. If it is ok to reuse now,
I'll just use the same for all hash-type maps.
Advice from slab expert would be great...
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