Add access control support to qemu bridge helper
[qemu.git] / qemu-bridge-helper.c
1 /*
2 * QEMU Bridge Helper
3 *
4 * Copyright IBM, Corp. 2011
5 *
6 * Authors:
7 * Anthony Liguori <aliguori@us.ibm.com>
8 * Richa Marwaha <rmarwah@linux.vnet.ibm.com>
9 * Corey Bryant <coreyb@linux.vnet.ibm.com>
10 *
11 * This work is licensed under the terms of the GNU GPL, version 2. See
12 * the COPYING file in the top-level directory.
13 *
14 */
15
16 #include "config-host.h"
17
18 #include <stdio.h>
19 #include <errno.h>
20 #include <fcntl.h>
21 #include <unistd.h>
22 #include <string.h>
23 #include <stdlib.h>
24 #include <stdbool.h>
25 #include <ctype.h>
26 #include <glib.h>
27
28 #include <sys/types.h>
29 #include <sys/ioctl.h>
30 #include <sys/socket.h>
31 #include <sys/un.h>
32 #include <sys/prctl.h>
33
34 #include <net/if.h>
35
36 #include <linux/sockios.h>
37
38 #include "qemu-queue.h"
39
40 #include "net/tap-linux.h"
41
42 #define DEFAULT_ACL_FILE CONFIG_QEMU_CONFDIR "/bridge.conf"
43
44 enum {
45 ACL_ALLOW = 0,
46 ACL_ALLOW_ALL,
47 ACL_DENY,
48 ACL_DENY_ALL,
49 };
50
51 typedef struct ACLRule {
52 int type;
53 char iface[IFNAMSIZ];
54 QSIMPLEQ_ENTRY(ACLRule) entry;
55 } ACLRule;
56
57 typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;
58
59 static void usage(void)
60 {
61 fprintf(stderr,
62 "Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
63 }
64
65 static int parse_acl_file(const char *filename, ACLList *acl_list)
66 {
67 FILE *f;
68 char line[4096];
69 ACLRule *acl_rule;
70
71 f = fopen(filename, "r");
72 if (f == NULL) {
73 return -1;
74 }
75
76 while (fgets(line, sizeof(line), f) != NULL) {
77 char *ptr = line;
78 char *cmd, *arg, *argend;
79
80 while (isspace(*ptr)) {
81 ptr++;
82 }
83
84 /* skip comments and empty lines */
85 if (*ptr == '#' || *ptr == 0) {
86 continue;
87 }
88
89 cmd = ptr;
90 arg = strchr(cmd, ' ');
91 if (arg == NULL) {
92 arg = strchr(cmd, '\t');
93 }
94
95 if (arg == NULL) {
96 fprintf(stderr, "Invalid config line:\n %s\n", line);
97 fclose(f);
98 errno = EINVAL;
99 return -1;
100 }
101
102 *arg = 0;
103 arg++;
104 while (isspace(*arg)) {
105 arg++;
106 }
107
108 argend = arg + strlen(arg);
109 while (arg != argend && isspace(*(argend - 1))) {
110 argend--;
111 }
112 *argend = 0;
113
114 if (strcmp(cmd, "deny") == 0) {
115 acl_rule = g_malloc(sizeof(*acl_rule));
116 if (strcmp(arg, "all") == 0) {
117 acl_rule->type = ACL_DENY_ALL;
118 } else {
119 acl_rule->type = ACL_DENY;
120 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
121 }
122 QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
123 } else if (strcmp(cmd, "allow") == 0) {
124 acl_rule = g_malloc(sizeof(*acl_rule));
125 if (strcmp(arg, "all") == 0) {
126 acl_rule->type = ACL_ALLOW_ALL;
127 } else {
128 acl_rule->type = ACL_ALLOW;
129 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
130 }
131 QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
132 } else if (strcmp(cmd, "include") == 0) {
133 /* ignore errors */
134 parse_acl_file(arg, acl_list);
135 } else {
136 fprintf(stderr, "Unknown command `%s'\n", cmd);
137 fclose(f);
138 errno = EINVAL;
139 return -1;
140 }
141 }
142
143 fclose(f);
144
145 return 0;
146 }
147
148 static bool has_vnet_hdr(int fd)
149 {
150 unsigned int features = 0;
151
152 if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
153 return false;
154 }
155
156 if (!(features & IFF_VNET_HDR)) {
157 return false;
158 }
159
160 return true;
161 }
162
163 static void prep_ifreq(struct ifreq *ifr, const char *ifname)
164 {
165 memset(ifr, 0, sizeof(*ifr));
166 snprintf(ifr->ifr_name, IFNAMSIZ, "%s", ifname);
167 }
168
169 static int send_fd(int c, int fd)
170 {
171 char msgbuf[CMSG_SPACE(sizeof(fd))];
172 struct msghdr msg = {
173 .msg_control = msgbuf,
174 .msg_controllen = sizeof(msgbuf),
175 };
176 struct cmsghdr *cmsg;
177 struct iovec iov;
178 char req[1] = { 0x00 };
179
180 cmsg = CMSG_FIRSTHDR(&msg);
181 cmsg->cmsg_level = SOL_SOCKET;
182 cmsg->cmsg_type = SCM_RIGHTS;
183 cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
184 msg.msg_controllen = cmsg->cmsg_len;
185
186 iov.iov_base = req;
187 iov.iov_len = sizeof(req);
188
189 msg.msg_iov = &iov;
190 msg.msg_iovlen = 1;
191 memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
192
193 return sendmsg(c, &msg, 0);
194 }
195
196 int main(int argc, char **argv)
197 {
198 struct ifreq ifr;
199 int fd, ctlfd, unixfd = -1;
200 int use_vnet = 0;
201 int mtu;
202 const char *bridge = NULL;
203 char iface[IFNAMSIZ];
204 int index;
205 ACLRule *acl_rule;
206 ACLList acl_list;
207 int access_allowed, access_denied;
208 int ret = EXIT_SUCCESS;
209
210 /* parse arguments */
211 for (index = 1; index < argc; index++) {
212 if (strcmp(argv[index], "--use-vnet") == 0) {
213 use_vnet = 1;
214 } else if (strncmp(argv[index], "--br=", 5) == 0) {
215 bridge = &argv[index][5];
216 } else if (strncmp(argv[index], "--fd=", 5) == 0) {
217 unixfd = atoi(&argv[index][5]);
218 } else {
219 usage();
220 return EXIT_FAILURE;
221 }
222 }
223
224 if (bridge == NULL || unixfd == -1) {
225 usage();
226 return EXIT_FAILURE;
227 }
228
229 /* parse default acl file */
230 QSIMPLEQ_INIT(&acl_list);
231 if (parse_acl_file(DEFAULT_ACL_FILE, &acl_list) == -1) {
232 fprintf(stderr, "failed to parse default acl file `%s'\n",
233 DEFAULT_ACL_FILE);
234 ret = EXIT_FAILURE;
235 goto cleanup;
236 }
237
238 /* validate bridge against acl -- default policy is to deny
239 * according acl policy if we have a deny and allow both
240 * then deny should always win over allow
241 */
242 access_allowed = 0;
243 access_denied = 0;
244 QSIMPLEQ_FOREACH(acl_rule, &acl_list, entry) {
245 switch (acl_rule->type) {
246 case ACL_ALLOW_ALL:
247 access_allowed = 1;
248 break;
249 case ACL_ALLOW:
250 if (strcmp(bridge, acl_rule->iface) == 0) {
251 access_allowed = 1;
252 }
253 break;
254 case ACL_DENY_ALL:
255 access_denied = 1;
256 break;
257 case ACL_DENY:
258 if (strcmp(bridge, acl_rule->iface) == 0) {
259 access_denied = 1;
260 }
261 break;
262 }
263 }
264
265 if ((access_allowed == 0) || (access_denied == 1)) {
266 fprintf(stderr, "access denied by acl file\n");
267 ret = EXIT_FAILURE;
268 goto cleanup;
269 }
270
271 /* open a socket to use to control the network interfaces */
272 ctlfd = socket(AF_INET, SOCK_STREAM, 0);
273 if (ctlfd == -1) {
274 fprintf(stderr, "failed to open control socket: %s\n", strerror(errno));
275 ret = EXIT_FAILURE;
276 goto cleanup;
277 }
278
279 /* open the tap device */
280 fd = open("/dev/net/tun", O_RDWR);
281 if (fd == -1) {
282 fprintf(stderr, "failed to open /dev/net/tun: %s\n", strerror(errno));
283 ret = EXIT_FAILURE;
284 goto cleanup;
285 }
286
287 /* request a tap device, disable PI, and add vnet header support if
288 * requested and it's available. */
289 prep_ifreq(&ifr, "tap%d");
290 ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
291 if (use_vnet && has_vnet_hdr(fd)) {
292 ifr.ifr_flags |= IFF_VNET_HDR;
293 }
294
295 if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
296 fprintf(stderr, "failed to create tun device: %s\n", strerror(errno));
297 ret = EXIT_FAILURE;
298 goto cleanup;
299 }
300
301 /* save tap device name */
302 snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);
303
304 /* get the mtu of the bridge */
305 prep_ifreq(&ifr, bridge);
306 if (ioctl(ctlfd, SIOCGIFMTU, &ifr) == -1) {
307 fprintf(stderr, "failed to get mtu of bridge `%s': %s\n",
308 bridge, strerror(errno));
309 ret = EXIT_FAILURE;
310 goto cleanup;
311 }
312
313 /* save mtu */
314 mtu = ifr.ifr_mtu;
315
316 /* set the mtu of the interface based on the bridge */
317 prep_ifreq(&ifr, iface);
318 ifr.ifr_mtu = mtu;
319 if (ioctl(ctlfd, SIOCSIFMTU, &ifr) == -1) {
320 fprintf(stderr, "failed to set mtu of device `%s' to %d: %s\n",
321 iface, mtu, strerror(errno));
322 ret = EXIT_FAILURE;
323 goto cleanup;
324 }
325
326 /* add the interface to the bridge */
327 prep_ifreq(&ifr, bridge);
328 ifr.ifr_ifindex = if_nametoindex(iface);
329
330 if (ioctl(ctlfd, SIOCBRADDIF, &ifr) == -1) {
331 fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
332 iface, bridge, strerror(errno));
333 ret = EXIT_FAILURE;
334 goto cleanup;
335 }
336
337 /* bring the interface up */
338 prep_ifreq(&ifr, iface);
339 if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
340 fprintf(stderr, "failed to get interface flags for `%s': %s\n",
341 iface, strerror(errno));
342 ret = EXIT_FAILURE;
343 goto cleanup;
344 }
345
346 ifr.ifr_flags |= IFF_UP;
347 if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
348 fprintf(stderr, "failed to bring up interface `%s': %s\n",
349 iface, strerror(errno));
350 ret = EXIT_FAILURE;
351 goto cleanup;
352 }
353
354 /* write fd to the domain socket */
355 if (send_fd(unixfd, fd) == -1) {
356 fprintf(stderr, "failed to write fd to unix socket: %s\n",
357 strerror(errno));
358 ret = EXIT_FAILURE;
359 goto cleanup;
360 }
361
362 /* ... */
363
364 /* profit! */
365
366 cleanup:
367
368 while ((acl_rule = QSIMPLEQ_FIRST(&acl_list)) != NULL) {
369 QSIMPLEQ_REMOVE_HEAD(&acl_list, entry);
370 g_free(acl_rule);
371 }
372
373 return ret;
374 }