net/802/psnap.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *      SNAP data link layer. Derived from 802.2
   4  *
   5  *              Alan Cox <alan@lxorguk.ukuu.org.uk>,
   6  *              from the 802.2 layer by Greg Page.
   7  *              Merged in additions from Greg Page's psnap.c.
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/netdevice.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/slab.h>
  14 #include <net/datalink.h>
  15 #include <net/llc.h>
  16 #include <net/psnap.h>
  17 #include <linux/mm.h>
  18 #include <linux/in.h>
  19 #include <linux/init.h>
  20 #include <linux/rculist.h>
  21
  22 static LIST_HEAD(snap_list);
  23 static DEFINE_SPINLOCK(snap_lock);
  24 static struct llc_sap *snap_sap;
  25
  26 /*
  27  *      Find a snap client by matching the 5 bytes.
  28  */
  29 static struct datalink_proto *find_snap_client(const unsigned char *desc)
  30 {
  31         struct datalink_proto *proto = NULL, *p;
  32
  33         list_for_each_entry_rcu(p, &snap_list, node) {
  34                 if (!memcmp(p->type, desc, 5)) {
  35                         proto = p;
  36                         break;
  37                 }
  38         }
  39         return proto;
  40 }
  41
  42 /*
  43  *      A SNAP packet has arrived
  44  */
  45 static int snap_rcv(struct sk_buff *skb, struct net_device *dev,
  46                     struct packet_type *pt, struct net_device *orig_dev)
  47 {
  48         int rc = 1;
  49         struct datalink_proto *proto;
  50         static struct packet_type snap_packet_type = {
  51                 .type = cpu_to_be16(ETH_P_SNAP),
  52         };
  53
  54         if (unlikely(!pskb_may_pull(skb, 5)))
  55                 goto drop;
  56
  57         rcu_read_lock();
  58         proto = find_snap_client(skb_transport_header(skb));
  59         if (proto) {
  60                 /* Pass the frame on. */
  61                 skb->transport_header += 5;
  62                 skb_pull_rcsum(skb, 5);
  63                 rc = proto->rcvfunc(skb, dev, &snap_packet_type, orig_dev);
  64         }
  65         rcu_read_unlock();
  66
  67         if (unlikely(!proto))
  68                 goto drop;
  69
  70 out:
  71         return rc;
  72
  73 drop:
  74         kfree_skb(skb);
  75         goto out;
  76 }
  77
  78 /*
  79  *      Put a SNAP header on a frame and pass to 802.2
  80  */
  81 static int snap_request(struct datalink_proto *dl,
  82                         struct sk_buff *skb, u8 *dest)
  83 {
  84         memcpy(skb_push(skb, 5), dl->type, 5);
  85         llc_build_and_send_ui_pkt(snap_sap, skb, dest, snap_sap->laddr.lsap);
  86         return 0;
  87 }
  88
  89 /*
  90  *      Set up the SNAP layer
  91  */
  92 EXPORT_SYMBOL(register_snap_client);
  93 EXPORT_SYMBOL(unregister_snap_client);
  94
  95 static const char snap_err_msg[] __initconst =
  96         KERN_CRIT "SNAP - unable to register with 802.2\n";
  97
  98 static int __init snap_init(void)
  99 {
 100         snap_sap = llc_sap_open(0xAA, snap_rcv);
 101         if (!snap_sap) {
 102                 printk(snap_err_msg);
 103                 return -EBUSY;
 104         }
 105
 106         return 0;
 107 }
 108
 109 module_init(snap_init);
 110
 111 static void __exit snap_exit(void)
 112 {
 113         llc_sap_put(snap_sap);
 114 }
 115
 116 module_exit(snap_exit);
 117
 118
 119 /*
 120  *      Register SNAP clients. We don't yet use this for IP.
 121  */
 122 struct datalink_proto *register_snap_client(const unsigned char *desc,
 123                                             int (*rcvfunc)(struct sk_buff *,
 124                                                            struct net_device *,
 125                                                            struct packet_type *,
 126                                                            struct net_device *))
 127 {
 128         struct datalink_proto *proto = NULL;
 129
 130         spin_lock_bh(&snap_lock);
 131
 132         if (find_snap_client(desc))
 133                 goto out;
 134
 135         proto = kmalloc(sizeof(*proto), GFP_ATOMIC);
 136         if (proto) {
 137                 memcpy(proto->type, desc, 5);
 138                 proto->rcvfunc          = rcvfunc;
 139                 proto->header_length    = 5 + 3; /* snap + 802.2 */
 140                 proto->request          = snap_request;
 141                 list_add_rcu(&proto->node, &snap_list);
 142         }
 143 out:
 144         spin_unlock_bh(&snap_lock);
 145
 146         return proto;
 147 }
 148
 149 /*
 150  *      Unregister SNAP clients. Protocols no longer want to play with us ...
 151  */
 152 void unregister_snap_client(struct datalink_proto *proto)
 153 {
 154         spin_lock_bh(&snap_lock);
 155         list_del_rcu(&proto->node);
 156         spin_unlock_bh(&snap_lock);
 157
 158         synchronize_net();
 159
 160         kfree(proto);
 161 }
 162
 163 MODULE_LICENSE("GPL");