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 
11 #include "utils/common.h"
12 #include "common/dhcp.h"
13 #include "l2_packet/l2_packet.h"
14 #include "hostapd.h"
15 #include "sta_info.h"
16 #include "ap_drv_ops.h"
17 #include "x_snoop.h"
18 #include "dhcp_snoop.h"
19 
20 
ipaddr_str(u32 addr)21 static const char * ipaddr_str(u32 addr)
22 {
23 	static char buf[17];
24 
25 	os_snprintf(buf, sizeof(buf), "%u.%u.%u.%u",
26 		    (addr >> 24) & 0xff, (addr >> 16) & 0xff,
27 		    (addr >> 8) & 0xff, addr & 0xff);
28 	return buf;
29 }
30 
31 
handle_dhcp(void * ctx,const u8 * src_addr,const u8 * buf,size_t len)32 static void handle_dhcp(void *ctx, const u8 *src_addr, const u8 *buf,
33 			size_t len)
34 {
35 	struct hostapd_data *hapd = ctx;
36 	const struct bootp_pkt *b;
37 	struct sta_info *sta;
38 	int exten_len;
39 	const u8 *end, *pos;
40 	int res, msgtype = 0, prefixlen = 32;
41 	u32 subnet_mask = 0;
42 	u16 tot_len;
43 
44 	exten_len = len - ETH_HLEN - (sizeof(*b) - sizeof(b->exten));
45 	if (exten_len < 4)
46 		return;
47 
48 	b = (const struct bootp_pkt *) &buf[ETH_HLEN];
49 	tot_len = ntohs(b->iph.tot_len);
50 	if (tot_len > (unsigned int) (len - ETH_HLEN))
51 		return;
52 
53 	if (WPA_GET_BE32(b->exten) != DHCP_MAGIC)
54 		return;
55 
56 	/* Parse DHCP options */
57 	end = (const u8 *) b + tot_len;
58 	pos = &b->exten[4];
59 	while (pos < end && *pos != DHCP_OPT_END) {
60 		const u8 *opt = pos++;
61 
62 		if (*opt == DHCP_OPT_PAD)
63 			continue;
64 
65 		if (pos >= end || 1 + *pos > end - pos)
66 			break;
67 		pos += *pos + 1;
68 		if (pos >= end)
69 			break;
70 
71 		switch (*opt) {
72 		case DHCP_OPT_SUBNET_MASK:
73 			if (opt[1] == 4)
74 				subnet_mask = WPA_GET_BE32(&opt[2]);
75 			if (subnet_mask == 0)
76 				return;
77 			while (!(subnet_mask & 0x1)) {
78 				subnet_mask >>= 1;
79 				prefixlen--;
80 			}
81 			break;
82 		case DHCP_OPT_MSG_TYPE:
83 			if (opt[1])
84 				msgtype = opt[2];
85 			break;
86 		default:
87 			break;
88 		}
89 	}
90 
91 	if (hapd->conf->disable_dgaf && is_broadcast_ether_addr(buf)) {
92 		for (sta = hapd->sta_list; sta; sta = sta->next) {
93 			if (!(sta->flags & WLAN_STA_AUTHORIZED))
94 				continue;
95 			x_snoop_mcast_to_ucast_convert_send(hapd, sta,
96 							    (u8 *) buf, len);
97 		}
98 	}
99 
100 	if (msgtype == DHCPACK) {
101 		if (b->your_ip == 0)
102 			return;
103 
104 		/* DHCPACK for DHCPREQUEST */
105 		sta = ap_get_sta(hapd, b->hw_addr);
106 		if (!sta)
107 			return;
108 
109 		wpa_printf(MSG_DEBUG, "dhcp_snoop: Found DHCPACK for " MACSTR
110 			   " @ IPv4 address %s/%d",
111 			   MAC2STR(sta->addr),
112 			   ipaddr_str(be_to_host32(b->your_ip)),
113 			   prefixlen);
114 
115 		if (sta->ipaddr == b->your_ip)
116 			return;
117 
118 		if (sta->ipaddr != 0) {
119 			wpa_printf(MSG_DEBUG,
120 				   "dhcp_snoop: Removing IPv4 address %s from the ip neigh table",
121 				   ipaddr_str(be_to_host32(sta->ipaddr)));
122 			hostapd_drv_br_delete_ip_neigh(hapd, 4,
123 						       (u8 *) &sta->ipaddr);
124 		}
125 
126 		res = hostapd_drv_br_add_ip_neigh(hapd, 4, (u8 *) &b->your_ip,
127 						  prefixlen, sta->addr);
128 		if (res) {
129 			wpa_printf(MSG_DEBUG,
130 				   "dhcp_snoop: Adding ip neigh table failed: %d",
131 				   res);
132 			return;
133 		}
134 		sta->ipaddr = b->your_ip;
135 	}
136 }
137 
138 
dhcp_snoop_init(struct hostapd_data * hapd)139 int dhcp_snoop_init(struct hostapd_data *hapd)
140 {
141 	hapd->sock_dhcp = x_snoop_get_l2_packet(hapd, handle_dhcp,
142 						L2_PACKET_FILTER_DHCP);
143 	if (hapd->sock_dhcp == NULL) {
144 		wpa_printf(MSG_DEBUG,
145 			   "dhcp_snoop: Failed to initialize L2 packet processing for DHCP packet: %s",
146 			   strerror(errno));
147 		return -1;
148 	}
149 
150 	return 0;
151 }
152 
153 
dhcp_snoop_deinit(struct hostapd_data * hapd)154 void dhcp_snoop_deinit(struct hostapd_data *hapd)
155 {
156 	l2_packet_deinit(hapd->sock_dhcp);
157 	hapd->sock_dhcp = NULL;
158 }
159