src/ap/dhcp_snoop.c

   1 /*
   2  * DHCP snooping for Proxy ARP
   3  * Copyright (c) 2014, Qualcomm Atheros, Inc.
   4  *
   5  * This software may be distributed under the terms of the BSD license.
   6  * See README for more details.
   7  */
   8
   9 #include "utils/includes.h"
  10 #include <netinet/ip.h>
  11 #include <netinet/udp.h>
  12
  13 #include "utils/common.h"
  14 #include "l2_packet/l2_packet.h"
  15 #include "hostapd.h"
  16 #include "sta_info.h"
  17 #include "ap_drv_ops.h"
  18 #include "x_snoop.h"
  19 #include "dhcp_snoop.h"
  20
  21 struct bootp_pkt {
  22         struct iphdr iph;
  23         struct udphdr udph;
  24         u8 op;
  25         u8 htype;
  26         u8 hlen;
  27         u8 hops;
  28         be32 xid;
  29         be16 secs;
  30         be16 flags;
  31         be32 client_ip;
  32         be32 your_ip;
  33         be32 server_ip;
  34         be32 relay_ip;
  35         u8 hw_addr[16];
  36         u8 serv_name[64];
  37         u8 boot_file[128];
  38         u8 exten[312];
  39 };
  40
  41 #define DHCPACK 5
  42 static const u8 ic_bootp_cookie[] = { 99, 130, 83, 99 };
  43
  44
  45 static void handle_dhcp(void *ctx, const u8 *src_addr, const u8 *buf,
  46                         size_t len)
  47 {
  48         struct hostapd_data *hapd = ctx;
  49         const struct bootp_pkt *b;
  50         struct sta_info *sta;
  51         int exten_len;
  52         const u8 *end, *pos;
  53         int res, msgtype = 0, prefixlen = 32;
  54         u32 subnet_mask = 0;
  55
  56         exten_len = len - ETH_HLEN - (sizeof(*b) - sizeof(b->exten));
  57         if (exten_len < 4)
  58                 return;
  59
  60         b = (const struct bootp_pkt *) &buf[ETH_HLEN];
  61         if (os_memcmp(b->exten, ic_bootp_cookie, ARRAY_SIZE(ic_bootp_cookie)))
  62                 return;
  63
  64         /* Parse DHCP options */
  65         end = (const u8 *) b + ntohs(b->iph.tot_len);
  66         pos = &b->exten[4];
  67         while (pos < end && *pos != 0xff) {
  68                 const u8 *opt = pos++;
  69
  70                 if (*opt == 0) /* padding */
  71                         continue;
  72
  73                 pos += *pos + 1;
  74                 if (pos >= end)
  75                         break;
  76
  77                 switch (*opt) {
  78                 case 1:  /* subnet mask */
  79                         if (opt[1] == 4)
  80                                 subnet_mask = WPA_GET_BE32(&opt[2]);
  81                         if (subnet_mask == 0)
  82                                 return;
  83                         while (!(subnet_mask & 0x1)) {
  84                                 subnet_mask >>= 1;
  85                                 prefixlen--;
  86                         }
  87                         break;
  88                 case 53: /* message type */
  89                         if (opt[1])
  90                                 msgtype = opt[2];
  91                         break;
  92                 default:
  93                         break;
  94                 }
  95         }
  96
  97         if (msgtype == DHCPACK) {
  98                 if (b->your_ip == 0)
  99                         return;
 100
 101                 /* DHCPACK for DHCPREQUEST */
 102                 sta = ap_get_sta(hapd, b->hw_addr);
 103                 if (!sta)
 104                         return;
 105
 106                 wpa_printf(MSG_DEBUG, "dhcp_snoop: Found DHCPACK for " MACSTR
 107                            " @ IPv4 address %X/%d",
 108                            MAC2STR(sta->addr), ntohl(b->your_ip), prefixlen);
 109
 110                 if (sta->ipaddr == b->your_ip)
 111                         return;
 112
 113                 if (sta->ipaddr != 0) {
 114                         wpa_printf(MSG_DEBUG,
 115                                    "dhcp_snoop: Removing IPv4 address %X from the ip neigh table",
 116                                    sta->ipaddr);
 117                         hostapd_drv_br_delete_ip_neigh(hapd, 4,
 118                                                        (u8 *) &sta->ipaddr);
 119                 }
 120
 121                 res = hostapd_drv_br_add_ip_neigh(hapd, 4, (u8 *) &b->your_ip,
 122                                                   prefixlen, sta->addr);
 123                 if (res) {
 124                         wpa_printf(MSG_DEBUG,
 125                                    "dhcp_snoop: Adding ip neigh table failed: %d",
 126                                    res);
 127                         return;
 128                 }
 129                 sta->ipaddr = b->your_ip;
 130         }
 131
 132         if (hapd->conf->disable_dgaf && is_broadcast_ether_addr(buf)) {
 133                 for (sta = hapd->sta_list; sta; sta = sta->next)
 134                         x_snoop_mcast_to_ucast_convert_send(hapd, sta,
 135                                                             (u8 *) buf, len);
 136         }
 137 }
 138
 139
 140 int dhcp_snoop_init(struct hostapd_data *hapd)
 141 {
 142         hapd->sock_dhcp = x_snoop_get_l2_packet(hapd, handle_dhcp,
 143                                                 L2_PACKET_FILTER_DHCP);
 144         if (hapd->sock_dhcp == NULL) {
 145                 wpa_printf(MSG_DEBUG,
 146                            "dhcp_snoop: Failed to initialize L2 packet processing for DHCP packet: %s",
 147                            strerror(errno));
 148                 return -1;
 149         }
 150
 151         return 0;
 152 }
 153
 154
 155 void dhcp_snoop_deinit(struct hostapd_data *hapd)
 156 {
 157         l2_packet_deinit(hapd->sock_dhcp);
 158 }