net/802/stp.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *      STP SAP demux
   4  *
   5  *      Copyright (c) 2008 Patrick McHardy <kaber@trash.net>
   6  */
   7 #include <linux/mutex.h>
   8 #include <linux/skbuff.h>
   9 #include <linux/etherdevice.h>
  10 #include <linux/llc.h>
  11 #include <linux/slab.h>
  12 #include <linux/module.h>
  13 #include <net/llc.h>
  14 #include <net/llc_pdu.h>
  15 #include <net/stp.h>
  16
  17 /* 01:80:c2:00:00:20 - 01:80:c2:00:00:2F */
  18 #define GARP_ADDR_MIN   0x20
  19 #define GARP_ADDR_MAX   0x2F
  20 #define GARP_ADDR_RANGE (GARP_ADDR_MAX - GARP_ADDR_MIN)
  21
  22 static const struct stp_proto __rcu *garp_protos[GARP_ADDR_RANGE + 1] __read_mostly;
  23 static const struct stp_proto __rcu *stp_proto __read_mostly;
  24
  25 static struct llc_sap *sap __read_mostly;
  26 static unsigned int sap_registered;
  27 static DEFINE_MUTEX(stp_proto_mutex);
  28
  29 /* Called under rcu_read_lock from LLC */
  30 static int stp_pdu_rcv(struct sk_buff *skb, struct net_device *dev,
  31                        struct packet_type *pt, struct net_device *orig_dev)
  32 {
  33         const struct ethhdr *eh = eth_hdr(skb);
  34         const struct llc_pdu_un *pdu = llc_pdu_un_hdr(skb);
  35         const struct stp_proto *proto;
  36
  37         if (pdu->ssap != LLC_SAP_BSPAN ||
  38             pdu->dsap != LLC_SAP_BSPAN ||
  39             pdu->ctrl_1 != LLC_PDU_TYPE_U)
  40                 goto err;
  41
  42         if (eh->h_dest[5] >= GARP_ADDR_MIN && eh->h_dest[5] <= GARP_ADDR_MAX) {
  43                 proto = rcu_dereference(garp_protos[eh->h_dest[5] -
  44                                                     GARP_ADDR_MIN]);
  45                 if (proto &&
  46                     !ether_addr_equal(eh->h_dest, proto->group_address))
  47                         goto err;
  48         } else
  49                 proto = rcu_dereference(stp_proto);
  50
  51         if (!proto)
  52                 goto err;
  53
  54         proto->rcv(proto, skb, dev);
  55         return 0;
  56
  57 err:
  58         kfree_skb(skb);
  59         return 0;
  60 }
  61
  62 int stp_proto_register(const struct stp_proto *proto)
  63 {
  64         int err = 0;
  65
  66         mutex_lock(&stp_proto_mutex);
  67         if (sap_registered++ == 0) {
  68                 sap = llc_sap_open(LLC_SAP_BSPAN, stp_pdu_rcv);
  69                 if (!sap) {
  70                         err = -ENOMEM;
  71                         goto out;
  72                 }
  73         }
  74         if (is_zero_ether_addr(proto->group_address))
  75                 rcu_assign_pointer(stp_proto, proto);
  76         else
  77                 rcu_assign_pointer(garp_protos[proto->group_address[5] -
  78                                                GARP_ADDR_MIN], proto);
  79 out:
  80         mutex_unlock(&stp_proto_mutex);
  81         return err;
  82 }
  83 EXPORT_SYMBOL_GPL(stp_proto_register);
  84
  85 void stp_proto_unregister(const struct stp_proto *proto)
  86 {
  87         mutex_lock(&stp_proto_mutex);
  88         if (is_zero_ether_addr(proto->group_address))
  89                 RCU_INIT_POINTER(stp_proto, NULL);
  90         else
  91                 RCU_INIT_POINTER(garp_protos[proto->group_address[5] -
  92                                                GARP_ADDR_MIN], NULL);
  93         synchronize_rcu();
  94
  95         if (--sap_registered == 0)
  96                 llc_sap_put(sap);
  97         mutex_unlock(&stp_proto_mutex);
  98 }
  99 EXPORT_SYMBOL_GPL(stp_proto_unregister);
 100
 101 MODULE_DESCRIPTION("SAP demux for IEEE 802.1D Spanning Tree Protocol (STP)");
 102 MODULE_LICENSE("GPL");