devmap: Use bpf_map_area_alloc() for allocating hash buckets

Syzkaller discovered that creating a hash of type devmap_hash with a large
number of entries can hit the memory allocator limit for allocating
contiguous memory regions. There's really no reason to use kmalloc_array()
directly in the devmap code, so just switch it to the existing
bpf_map_area_alloc() function that is used elsewhere.

Fixes: 6f9d451 ("xdp: Add devmap_hash map type for looking up devices by hashed index")
Reported-by: Xiumei Mu <xmu@redhat.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200616142829.114173-1-toke@redhat.com

kernel/bpf/devmap.c

@@ -86,12 +86,13 @@ static DEFINE_PER_CPU(struct list_head, dev_flush_list);
 static DEFINE_SPINLOCK(dev_map_lock);
 static LIST_HEAD(dev_map_list);
 
-static struct hlist_head *dev_map_create_hash(unsigned int entries)
+static struct hlist_head *dev_map_create_hash(unsigned int entries,
+					      int numa_node)
 {
 	int i;
 	struct hlist_head *hash;
 
-	hash = kmalloc_array(entries, sizeof(*hash), GFP_KERNEL);
+	hash = bpf_map_area_alloc(entries * sizeof(*hash), numa_node);
 	if (hash != NULL)
 		for (i = 0; i < entries; i++)
 			INIT_HLIST_HEAD(&hash[i]);
@@ -145,7 +146,8 @@ static int dev_map_init_map(struct bpf_dtab *dtab, union bpf_attr *attr)
 		return -EINVAL;
 
 	if (attr->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
-		dtab->dev_index_head = dev_map_create_hash(dtab->n_buckets);
+		dtab->dev_index_head = dev_map_create_hash(dtab->n_buckets,
+							   dtab->map.numa_node);
 		if (!dtab->dev_index_head)
 			goto free_charge;
 
@@ -232,7 +234,7 @@ static void dev_map_free(struct bpf_map *map)
 			}
 		}
 
-		kfree(dtab->dev_index_head);
+		bpf_map_area_free(dtab->dev_index_head);
 	} else {
 		for (i = 0; i < dtab->map.max_entries; i++) {
 			struct bpf_dtab_netdev *dev;