batman-adv: Only read OGM2 tvlv_len after buffer len check

 * batadv_v_ogm_aggr_packet() - checks if there is another OGM aggregated

 * @buff_pos: current position in the skb

 * @packet_len: total length of the skb

 * @tvlv_len: tvlv length of the previously considered OGM

 * @ogm2_packet: potential OGM2 in buffer

 *

 * Return: true if there is enough space for another OGM, false otherwise.

 */

static bool batadv_v_ogm_aggr_packet(int buff_pos, int packet_len,

				     __be16 tvlv_len)

static bool

batadv_v_ogm_aggr_packet(int buff_pos, int packet_len,

			 const struct batadv_ogm2_packet *ogm2_packet)

{

	int next_buff_pos = 0;

	next_buff_pos += buff_pos + BATADV_OGM2_HLEN;

	next_buff_pos += ntohs(tvlv_len);

	/* check if there is enough space for the header */

	next_buff_pos += buff_pos + sizeof(*ogm2_packet);

	if (next_buff_pos > packet_len)

		return false;

	/* check if there is enough space for the optional TVLV */

	next_buff_pos += ntohs(ogm2_packet->tvlv_len);

	return (next_buff_pos <= packet_len) &&

	       (next_buff_pos <= BATADV_MAX_AGGREGATION_BYTES);

	ogm_packet = (struct batadv_ogm2_packet *)skb->data;

	while (batadv_v_ogm_aggr_packet(ogm_offset, skb_headlen(skb),

					ogm_packet->tvlv_len)) {

					ogm_packet)) {

		batadv_v_ogm_process(skb, ogm_offset, if_incoming);

		ogm_offset += BATADV_OGM2_HLEN;