br_stp_bpdu.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *	Spanning tree protocol; BPDU handling
 *	Linux ethernet bridge
 *
 *	Authors:
 *	Lennert Buytenhek		<[email protected]>
 */

#include <linux/kernel.h>
#include <linux/netfilter_bridge.h>
#include <linux/etherdevice.h>
#include <linux/llc.h>
#include <linux/slab.h>
#include <linux/pkt_sched.h>
#include <net/net_namespace.h>
#include <net/llc.h>
#include <net/llc_pdu.h>
#include <net/stp.h>
#include <linux/unaligned.h>

#include "br_private.h"
#include "br_private_stp.h"

#define STP_HZ		256

#define LLC_RESERVE sizeof(struct llc_pdu_un)

static int br_send_bpdu_finish(struct net *net, struct sock *sk,
			       struct sk_buff *skb)
{
	return dev_queue_xmit(skb);
}

static void br_send_bpdu(struct net_bridge_port *p,
			 const unsigned char *data, int length)
{
	struct sk_buff *skb;

	skb = dev_alloc_skb(length+LLC_RESERVE);
	if (!skb)
		return;

	skb->dev = p->dev;
	skb->protocol = htons(ETH_P_802_2);
	skb->priority = TC_PRIO_CONTROL;

	skb_reserve(skb, LLC_RESERVE);
	__skb_put_data(skb, data, length);

	llc_pdu_header_init(skb, LLC_PDU_TYPE_U, LLC_SAP_BSPAN,
			    LLC_SAP_BSPAN, LLC_PDU_CMD);
	llc_pdu_init_as_ui_cmd(skb);

	llc_mac_hdr_init(skb, p->dev->dev_addr, p->br->group_addr);

	skb_reset_mac_header(skb);

	NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_OUT,
		dev_net(p->dev), NULL, skb, NULL, skb->dev,
		br_send_bpdu_finish);
}

static inline void br_set_ticks(unsigned char *dest, int j)
{
	unsigned long ticks = (STP_HZ * j)/ HZ;

	put_unaligned_be16(ticks, dest);
}

static inline int br_get_ticks(const unsigned char *src)
{
	unsigned long ticks = get_unaligned_be16(src);

	return DIV_ROUND_UP(ticks * HZ, STP_HZ);
}

/* called under bridge lock */
void br_send_config_bpdu(struct net_bridge_port *p, struct br_config_bpdu *bpdu)
{
	unsigned char buf[35];

	if (p->br->stp_enabled != BR_KERNEL_STP)
		return;

	buf[0] = 0;
	buf[1] = 0;
	buf[2] = 0;
	buf[3] = BPDU_TYPE_CONFIG;
	buf[4] = (bpdu->topology_change ? 0x01 : 0) |
		(bpdu->topology_change_ack ? 0x80 : 0);
	buf[5] = bpdu->root.prio[0];
	buf[6] = bpdu->root.prio[1];
	buf[7] = bpdu->root.addr[0];
	buf[8] = bpdu->root.addr[1];
	buf[9] = bpdu->root.addr[2];
	buf[10] = bpdu->root.addr[3];
	buf[11] = bpdu->root.addr[4];
	buf[12] = bpdu->root.addr[5];
	buf[13] = (bpdu->root_path_cost >> 24) & 0xFF;
	buf[14] = (bpdu->root_path_cost >> 16) & 0xFF;
	buf[15] = (bpdu->root_path_cost >> 8) & 0xFF;
	buf[16] = bpdu->root_path_cost & 0xFF;
	buf[17] = bpdu->bridge_id.prio[0];
	buf[18] = bpdu->bridge_id.prio[1];
	buf[19] = bpdu->bridge_id.addr[0];
	buf[20] = bpdu->bridge_id.addr[1];
	buf[21] = bpdu->bridge_id.addr[2];
	buf[22] = bpdu->bridge_id.addr[3];
	buf[23] = bpdu->bridge_id.addr[4];
	buf[24] = bpdu->bridge_id.addr[5];
	buf[25] = (bpdu->port_id >> 8) & 0xFF;
	buf[26] = bpdu->port_id & 0xFF;

	br_set_ticks(buf+27, bpdu->message_age);
	br_set_ticks(buf+29, bpdu->max_age);
	br_set_ticks(buf+31, bpdu->hello_time);
	br_set_ticks(buf+33, bpdu->forward_delay);

	br_send_bpdu(p, buf, 35);

	p->stp_xstats.tx_bpdu++;
}

/* called under bridge lock */
void br_send_tcn_bpdu(struct net_bridge_port *p)
{
	unsigned char buf[4];

	if (p->br->stp_enabled != BR_KERNEL_STP)
		return;

	buf[0] = 0;
	buf[1] = 0;
	buf[2] = 0;
	buf[3] = BPDU_TYPE_TCN;
	br_send_bpdu(p, buf, 4);

	p->stp_xstats.tx_tcn++;
}

/*
 * Called from llc.
 *
 * NO locks, but rcu_read_lock
 */
void br_stp_rcv(const struct stp_proto *proto, struct sk_buff *skb,
		struct net_device *dev)
{
	struct net_bridge_port *p;
	struct net_bridge *br;
	const unsigned char *buf;

	if (!pskb_may_pull(skb, 4))
		goto err;

	/* compare of protocol id and version */
	buf = skb->data;
	if (buf[0] != 0 || buf[1] != 0 || buf[2] != 0)
		goto err;

	p = br_port_get_check_rcu(dev);
	if (!p)
		goto err;

	br = p->br;
	spin_lock(&br->lock);

	if (br->stp_enabled != BR_KERNEL_STP)
		goto out;

	if (!(br->dev->flags & IFF_UP))
		goto out;

	if (p->state == BR_STATE_DISABLED)
		goto out;

	if (!ether_addr_equal(eth_hdr(skb)->h_dest, br->group_addr))
		goto out;

	if (p->flags & BR_BPDU_GUARD) {
		br_notice(br, "BPDU received on blocked port %u(%s)\n",
			  (unsigned int) p->port_no, p->dev->name);
		br_stp_disable_port(p);
		goto out;
	}

	buf = skb_pull(skb, 3);

	if (buf[0] == BPDU_TYPE_CONFIG) {
		struct br_config_bpdu bpdu;

		if (!pskb_may_pull(skb, 32))
			goto out;

		buf = skb->data;
		bpdu.topology_change = (buf[1] & 0x01) ? 1 : 0;
		bpdu.topology_change_ack = (buf[1] & 0x80) ? 1 : 0;

		bpdu.root.prio[0] = buf[2];
		bpdu.root.prio[1] = buf[3];
		bpdu.root.addr[0] = buf[4];
		bpdu.root.addr[1] = buf[5];
		bpdu.root.addr[2] = buf[6];
		bpdu.root.addr[3] = buf[7];
		bpdu.root.addr[4] = buf[8];
		bpdu.root.addr[5] = buf[9];
		bpdu.root_path_cost =
			(buf[10] << 24) |
			(buf[11] << 16) |
			(buf[12] << 8) |
			buf[13];
		bpdu.bridge_id.prio[0] = buf[14];
		bpdu.bridge_id.prio[1] = buf[15];
		bpdu.bridge_id.addr[0] = buf[16];
		bpdu.bridge_id.addr[1] = buf[17];
		bpdu.bridge_id.addr[2] = buf[18];
		bpdu.bridge_id.addr[3] = buf[19];
		bpdu.bridge_id.addr[4] = buf[20];
		bpdu.bridge_id.addr[5] = buf[21];
		bpdu.port_id = (buf[22] << 8) | buf[23];

		bpdu.message_age = br_get_ticks(buf+24);
		bpdu.max_age = br_get_ticks(buf+26);
		bpdu.hello_time = br_get_ticks(buf+28);
		bpdu.forward_delay = br_get_ticks(buf+30);

		if (bpdu.message_age > bpdu.max_age) {
			if (net_ratelimit())
				br_notice(p->br,
					  "port %u config from %pM"
					  " (message_age %ul > max_age %ul)\n",
					  p->port_no,
					  eth_hdr(skb)->h_source,
					  bpdu.message_age, bpdu.max_age);
			goto out;
		}

		br_received_config_bpdu(p, &bpdu);
	} else if (buf[0] == BPDU_TYPE_TCN) {
		br_received_tcn_bpdu(p);
	}
 out:
	spin_unlock(&br->lock);
 err:
	kfree_skb(skb);
}