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 12:57:23 -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 11:36 AM, Kees Cook <keescook@...omium.org> wrote:
>> +static struct bpf_map *htab_map_alloc(struct nlattr *attr[BPF_MAP_ATTR_MAX + 1])
>> +{
>> +       struct bpf_htab *htab;
>> +       int err, i;
>> +
>> +       htab = kmalloc(sizeof(*htab), GFP_USER);
>
> I'd prefer kzalloc here.

in this case I agree. will change, since it's not in critical path and we
can waste few cycles zeroing memory.

>> +       err = -ENOMEM;
>> +       htab->buckets = kmalloc(htab->n_buckets * sizeof(struct hlist_head),
>> +                               GFP_USER);
>
> I'd prefer kcalloc here, even though n_buckets can't currently trigger
> an integer overflow.

hmm, I would argue that kmalloc_array is a preferred way, but kcalloc ?
Few lines below the whole array is inited with INIT_HLIST_HEAD...

>> +       for (i = 0; i < htab->n_buckets; i++)
>> +               INIT_HLIST_HEAD(&htab->buckets[i]);

>> +       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
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