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 [off-list ref] wrote:

quoted

+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.

quoted

+       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...

quoted

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

quoted

+       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