1 /*
2 * Copyright 2012 Daniel Drown
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 *
16 * getroute.c - get an ip route
17 */
18 #include <string.h>
19 #include <errno.h>
20
21 #include <sys/socket.h>
22 #include <linux/netlink.h>
23 #include <linux/rtnetlink.h>
24 #include <arpa/inet.h>
25
26 #include <netlink/handlers.h>
27 #include <netlink/msg.h>
28
29 #include "getroute.h"
30 #include "netlink_callbacks.h"
31 #include "netlink_msg.h"
32
33 /* function: get_default_route_cb
34 * finds the default route with the request family and out interface and saves the gateway
35 * msg - netlink message
36 * data - (struct default_route_data) requested filters and response storage
37 */
get_default_route_cb(struct nl_msg * msg,void * data)38 static int get_default_route_cb(struct nl_msg *msg, void *data) {
39 struct rtmsg *rt_p;
40 struct rtattr *rta_p;
41 int rta_len;
42 struct default_route_data *default_route = data;
43 union anyip *this_gateway = NULL;
44 ssize_t this_gateway_size;
45 int this_interface_id = -1;
46
47 if(default_route->reply_found_route) { // we already found our route
48 return NL_OK;
49 }
50
51 rt_p = (struct rtmsg *)nlmsg_data(nlmsg_hdr(msg));
52 if(rt_p->rtm_dst_len != 0) { // not a default route
53 return NL_OK;
54 }
55 if((rt_p->rtm_family != default_route->request_family) || (rt_p->rtm_table != RT_TABLE_MAIN)) { // not a route we care about
56 return NL_OK;
57 }
58
59 rta_p = (struct rtattr *)RTM_RTA(rt_p);
60 rta_len = RTM_PAYLOAD(nlmsg_hdr(msg));
61 for(; RTA_OK(rta_p, rta_len); rta_p = RTA_NEXT(rta_p, rta_len)) {
62 switch(rta_p->rta_type) {
63 case RTA_GATEWAY:
64 this_gateway = RTA_DATA(rta_p);
65 this_gateway_size = RTA_PAYLOAD(rta_p);
66 break;
67 case RTA_OIF:
68 this_interface_id = *(int *)RTA_DATA(rta_p);
69 break;
70 default:
71 break;
72 }
73 }
74
75 if(this_interface_id == default_route->request_interface_id) {
76 default_route->reply_found_route = 1;
77 if(this_gateway != NULL) {
78 memcpy(&default_route->reply_gateway, this_gateway, this_gateway_size);
79 default_route->reply_has_gateway = 1;
80 } else {
81 default_route->reply_has_gateway = 0;
82 }
83 }
84 return NL_OK;
85 }
86
87 /* function: error_handler
88 * error callback for get_default_route
89 * nla - where the message came from
90 * err - netlink message
91 * arg - (int *) storage for the error number
92 */
error_handler(struct sockaddr_nl * nla,struct nlmsgerr * err,void * arg)93 static int error_handler(struct sockaddr_nl *nla, struct nlmsgerr *err, void *arg) {
94 int *retval = arg;
95 if(err->error < 0) { // error_handler called even on no error (NLMSG_ERROR reply type used)
96 *retval = err->error;
97 }
98 return NL_OK;
99 }
100
101 /* function: get_default_route
102 * finds the first default route with the given family and interface, returns the gateway (if it exists) in the struct
103 * default_route - requested family and interface, and response storage
104 */
get_default_route(struct default_route_data * default_route)105 int get_default_route(struct default_route_data *default_route) {
106 struct rtmsg msg;
107 struct nl_cb *callbacks = NULL;
108 struct nl_msg *nlmsg = NULL;
109 int retval = 0;
110
111 default_route->reply_has_gateway = 0;
112 default_route->reply_found_route = 0;
113
114 memset(&msg,'\0',sizeof(msg));
115 msg.rtm_family = default_route->request_family;
116 msg.rtm_table = RT_TABLE_MAIN;
117 msg.rtm_protocol = RTPROT_KERNEL;
118 msg.rtm_scope = RT_SCOPE_UNIVERSE;
119
120 callbacks = nl_cb_alloc(NL_CB_DEFAULT);
121 if(!callbacks) {
122 retval = -ENOMEM;
123 goto cleanup;
124 }
125 // get_default_route_cb sets the response fields in default_route
126 nl_cb_set(callbacks, NL_CB_VALID, NL_CB_CUSTOM, get_default_route_cb, default_route);
127 nl_cb_err(callbacks, NL_CB_CUSTOM, error_handler, &retval);
128
129 nlmsg = nlmsg_alloc_rtmsg(RTM_GETROUTE, NLM_F_REQUEST | NLM_F_ROOT, &msg);
130 if(!nlmsg) {
131 retval = -ENOMEM;
132 goto cleanup;
133 }
134 send_netlink_msg(nlmsg, callbacks);
135
136 cleanup:
137 if(callbacks)
138 nl_cb_put(callbacks);
139 if(nlmsg)
140 nlmsg_free(nlmsg);
141
142 return retval;
143 }
144