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

[Alexei Starovoitov]

On Wed, Jul 23, 2014 at 11:36 AM, Kees Cook <keescook@xxxxxxxxxxxx> 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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