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 * Known shortcomings:
17 * - There is no manual page
18 * - The syntax of the ACL file is not documented anywhere
19 * - parse_acl_file() doesn't report fopen() failure properly, fails
20 * to check ferror() after fgets() failure, arbitrarily truncates
21 * long lines, handles whitespace inconsistently, error messages
22 * don't point to the offending file and line, errors in included
23 * files are reported, but otherwise ignored, ...
24 */
25
26 #include "qemu/osdep.h"
27
28
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 #ifndef SIOCBRADDIF
39 #include <linux/if_bridge.h>
40 #endif
41
42 #include "qemu/queue.h"
43 #include "qemu/cutils.h"
44
45 #include "net/tap-linux.h"
46
47 #ifdef CONFIG_LIBCAP_NG
48 #include <cap-ng.h>
49 #endif
50
51 #define DEFAULT_ACL_FILE CONFIG_QEMU_CONFDIR "/bridge.conf"
52
53 enum {
54 ACL_ALLOW = 0,
55 ACL_ALLOW_ALL,
56 ACL_DENY,
57 ACL_DENY_ALL,
58 };
59
60 typedef struct ACLRule {
61 int type;
62 char iface[IFNAMSIZ];
63 QSIMPLEQ_ENTRY(ACLRule) entry;
64 } ACLRule;
65
66 typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;
67
usage(void)68 static void usage(void)
69 {
70 fprintf(stderr,
71 "Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
72 }
73
parse_acl_file(const char * filename,ACLList * acl_list)74 static int parse_acl_file(const char *filename, ACLList *acl_list)
75 {
76 FILE *f;
77 char line[4096];
78 ACLRule *acl_rule;
79
80 f = fopen(filename, "r");
81 if (f == NULL) {
82 return -1;
83 }
84
85 while (fgets(line, sizeof(line), f) != NULL) {
86 char *ptr = line;
87 char *cmd, *arg, *argend;
88
89 while (g_ascii_isspace(*ptr)) {
90 ptr++;
91 }
92
93 /* skip comments and empty lines */
94 if (*ptr == '#' || *ptr == 0) {
95 continue;
96 }
97
98 cmd = ptr;
99 arg = strchr(cmd, ' ');
100 if (arg == NULL) {
101 arg = strchr(cmd, '\t');
102 }
103
104 if (arg == NULL) {
105 fprintf(stderr, "Invalid config line:\n %s\n", line);
106 goto err;
107 }
108
109 *arg = 0;
110 arg++;
111 while (g_ascii_isspace(*arg)) {
112 arg++;
113 }
114
115 argend = arg + strlen(arg);
116 while (arg != argend && g_ascii_isspace(*(argend - 1))) {
117 argend--;
118 }
119 *argend = 0;
120
121 if (!g_str_equal(cmd, "include") && strlen(arg) >= IFNAMSIZ) {
122 fprintf(stderr, "name `%s' too long: %zu\n", arg, strlen(arg));
123 goto err;
124 }
125
126 if (strcmp(cmd, "deny") == 0) {
127 acl_rule = g_malloc(sizeof(*acl_rule));
128 if (strcmp(arg, "all") == 0) {
129 acl_rule->type = ACL_DENY_ALL;
130 } else {
131 acl_rule->type = ACL_DENY;
132 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
133 }
134 QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
135 } else if (strcmp(cmd, "allow") == 0) {
136 acl_rule = g_malloc(sizeof(*acl_rule));
137 if (strcmp(arg, "all") == 0) {
138 acl_rule->type = ACL_ALLOW_ALL;
139 } else {
140 acl_rule->type = ACL_ALLOW;
141 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
142 }
143 QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
144 } else if (strcmp(cmd, "include") == 0) {
145 /* ignore errors */
146 parse_acl_file(arg, acl_list);
147 } else {
148 fprintf(stderr, "Unknown command `%s'\n", cmd);
149 goto err;
150 }
151 }
152
153 fclose(f);
154 return 0;
155
156 err:
157 fclose(f);
158 errno = EINVAL;
159 return -1;
160
161 }
162
has_vnet_hdr(int fd)163 static bool has_vnet_hdr(int fd)
164 {
165 unsigned int features = 0;
166
167 if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
168 return false;
169 }
170
171 if (!(features & IFF_VNET_HDR)) {
172 return false;
173 }
174
175 return true;
176 }
177
prep_ifreq(struct ifreq * ifr,const char * ifname)178 static void prep_ifreq(struct ifreq *ifr, const char *ifname)
179 {
180 memset(ifr, 0, sizeof(*ifr));
181 snprintf(ifr->ifr_name, IFNAMSIZ, "%s", ifname);
182 }
183
send_fd(int c,int fd)184 static int send_fd(int c, int fd)
185 {
186 char msgbuf[CMSG_SPACE(sizeof(fd))];
187 struct msghdr msg = {
188 .msg_control = msgbuf,
189 .msg_controllen = sizeof(msgbuf),
190 };
191 struct cmsghdr *cmsg;
192 struct iovec iov;
193 char req[1] = { 0x00 };
194
195 cmsg = CMSG_FIRSTHDR(&msg);
196 cmsg->cmsg_level = SOL_SOCKET;
197 cmsg->cmsg_type = SCM_RIGHTS;
198 cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
199 msg.msg_controllen = cmsg->cmsg_len;
200
201 iov.iov_base = req;
202 iov.iov_len = sizeof(req);
203
204 msg.msg_iov = &iov;
205 msg.msg_iovlen = 1;
206 memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
207
208 return sendmsg(c, &msg, 0);
209 }
210
211 #ifdef CONFIG_LIBCAP_NG
drop_privileges(void)212 static int drop_privileges(void)
213 {
214 /* clear all capabilities */
215 capng_clear(CAPNG_SELECT_BOTH);
216
217 if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE | CAPNG_PERMITTED,
218 CAP_NET_ADMIN) < 0) {
219 return -1;
220 }
221
222 /* change to calling user's real uid and gid, retaining supplemental
223 * groups and CAP_NET_ADMIN */
224 if (capng_change_id(getuid(), getgid(), CAPNG_CLEAR_BOUNDING)) {
225 return -1;
226 }
227
228 return 0;
229 }
230 #endif
231
main(int argc,char ** argv)232 int main(int argc, char **argv)
233 {
234 struct ifreq ifr;
235 #ifndef SIOCBRADDIF
236 unsigned long ifargs[4];
237 #endif
238 int ifindex;
239 int fd = -1, ctlfd = -1, unixfd = -1;
240 int use_vnet = 0;
241 int mtu;
242 const char *bridge = NULL;
243 char iface[IFNAMSIZ];
244 int index;
245 ACLRule *acl_rule;
246 ACLList acl_list;
247 int access_allowed, access_denied;
248 int ret = EXIT_SUCCESS;
249 g_autofree char *acl_file = NULL;
250
251 #ifdef CONFIG_LIBCAP_NG
252 /* if we're run from an suid binary, immediately drop privileges preserving
253 * cap_net_admin */
254 if (geteuid() == 0 && getuid() != geteuid()) {
255 if (drop_privileges() == -1) {
256 fprintf(stderr, "failed to drop privileges\n");
257 return 1;
258 }
259 }
260 #endif
261
262 qemu_init_exec_dir(argv[0]);
263
264 /* parse arguments */
265 for (index = 1; index < argc; index++) {
266 if (strcmp(argv[index], "--use-vnet") == 0) {
267 use_vnet = 1;
268 } else if (strncmp(argv[index], "--br=", 5) == 0) {
269 bridge = &argv[index][5];
270 } else if (strncmp(argv[index], "--fd=", 5) == 0) {
271 unixfd = atoi(&argv[index][5]);
272 } else {
273 usage();
274 return EXIT_FAILURE;
275 }
276 }
277
278 if (bridge == NULL || unixfd == -1) {
279 usage();
280 return EXIT_FAILURE;
281 }
282 if (strlen(bridge) >= IFNAMSIZ) {
283 fprintf(stderr, "name `%s' too long: %zu\n", bridge, strlen(bridge));
284 return EXIT_FAILURE;
285 }
286
287 /* parse default acl file */
288 QSIMPLEQ_INIT(&acl_list);
289 acl_file = get_relocated_path(DEFAULT_ACL_FILE);
290 if (parse_acl_file(acl_file, &acl_list) == -1) {
291 fprintf(stderr, "failed to parse default acl file `%s'\n",
292 acl_file);
293 ret = EXIT_FAILURE;
294 goto cleanup;
295 }
296
297 /* validate bridge against acl -- default policy is to deny
298 * according acl policy if we have a deny and allow both
299 * then deny should always win over allow
300 */
301 access_allowed = 0;
302 access_denied = 0;
303 QSIMPLEQ_FOREACH(acl_rule, &acl_list, entry) {
304 switch (acl_rule->type) {
305 case ACL_ALLOW_ALL:
306 access_allowed = 1;
307 break;
308 case ACL_ALLOW:
309 if (strcmp(bridge, acl_rule->iface) == 0) {
310 access_allowed = 1;
311 }
312 break;
313 case ACL_DENY_ALL:
314 access_denied = 1;
315 break;
316 case ACL_DENY:
317 if (strcmp(bridge, acl_rule->iface) == 0) {
318 access_denied = 1;
319 }
320 break;
321 }
322 }
323
324 if ((access_allowed == 0) || (access_denied == 1)) {
325 fprintf(stderr, "access denied by acl file\n");
326 ret = EXIT_FAILURE;
327 goto cleanup;
328 }
329
330 /* open a socket to use to control the network interfaces */
331 ctlfd = socket(AF_INET, SOCK_STREAM, 0);
332 if (ctlfd == -1) {
333 fprintf(stderr, "failed to open control socket: %s\n", strerror(errno));
334 ret = EXIT_FAILURE;
335 goto cleanup;
336 }
337
338 /* open the tap device */
339 fd = open("/dev/net/tun", O_RDWR);
340 if (fd == -1) {
341 fprintf(stderr, "failed to open /dev/net/tun: %s\n", strerror(errno));
342 ret = EXIT_FAILURE;
343 goto cleanup;
344 }
345
346 /* request a tap device, disable PI, and add vnet header support if
347 * requested and it's available. */
348 prep_ifreq(&ifr, "tap%d");
349 ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
350 if (use_vnet && has_vnet_hdr(fd)) {
351 ifr.ifr_flags |= IFF_VNET_HDR;
352 }
353
354 if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
355 fprintf(stderr, "failed to create tun device: %s\n", strerror(errno));
356 ret = EXIT_FAILURE;
357 goto cleanup;
358 }
359
360 /* save tap device name */
361 snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);
362
363 /* get the mtu of the bridge */
364 prep_ifreq(&ifr, bridge);
365 if (ioctl(ctlfd, SIOCGIFMTU, &ifr) == -1) {
366 fprintf(stderr, "failed to get mtu of bridge `%s': %s\n",
367 bridge, strerror(errno));
368 ret = EXIT_FAILURE;
369 goto cleanup;
370 }
371
372 /* save mtu */
373 mtu = ifr.ifr_mtu;
374
375 /* set the mtu of the interface based on the bridge */
376 prep_ifreq(&ifr, iface);
377 ifr.ifr_mtu = mtu;
378 if (ioctl(ctlfd, SIOCSIFMTU, &ifr) == -1) {
379 fprintf(stderr, "failed to set mtu of device `%s' to %d: %s\n",
380 iface, mtu, strerror(errno));
381 ret = EXIT_FAILURE;
382 goto cleanup;
383 }
384
385 /* Linux uses the lowest enslaved MAC address as the MAC address of
386 * the bridge. Set MAC address to a high value so that it doesn't
387 * affect the MAC address of the bridge.
388 */
389 if (ioctl(ctlfd, SIOCGIFHWADDR, &ifr) < 0) {
390 fprintf(stderr, "failed to get MAC address of device `%s': %s\n",
391 iface, strerror(errno));
392 ret = EXIT_FAILURE;
393 goto cleanup;
394 }
395 ifr.ifr_hwaddr.sa_data[0] = 0xFE;
396 if (ioctl(ctlfd, SIOCSIFHWADDR, &ifr) < 0) {
397 fprintf(stderr, "failed to set MAC address of device `%s': %s\n",
398 iface, strerror(errno));
399 ret = EXIT_FAILURE;
400 goto cleanup;
401 }
402
403 /* add the interface to the bridge */
404 prep_ifreq(&ifr, bridge);
405 ifindex = if_nametoindex(iface);
406 #ifndef SIOCBRADDIF
407 ifargs[0] = BRCTL_ADD_IF;
408 ifargs[1] = ifindex;
409 ifargs[2] = 0;
410 ifargs[3] = 0;
411 ifr.ifr_data = (void *)ifargs;
412 ret = ioctl(ctlfd, SIOCDEVPRIVATE, &ifr);
413 #else
414 ifr.ifr_ifindex = ifindex;
415 ret = ioctl(ctlfd, SIOCBRADDIF, &ifr);
416 #endif
417 if (ret == -1) {
418 fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
419 iface, bridge, strerror(errno));
420 ret = EXIT_FAILURE;
421 goto cleanup;
422 }
423
424 /* bring the interface up */
425 prep_ifreq(&ifr, iface);
426 if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
427 fprintf(stderr, "failed to get interface flags for `%s': %s\n",
428 iface, strerror(errno));
429 ret = EXIT_FAILURE;
430 goto cleanup;
431 }
432
433 ifr.ifr_flags |= IFF_UP;
434 if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
435 fprintf(stderr, "failed to bring up interface `%s': %s\n",
436 iface, strerror(errno));
437 ret = EXIT_FAILURE;
438 goto cleanup;
439 }
440
441 /* write fd to the domain socket */
442 if (send_fd(unixfd, fd) == -1) {
443 fprintf(stderr, "failed to write fd to unix socket: %s\n",
444 strerror(errno));
445 ret = EXIT_FAILURE;
446 goto cleanup;
447 }
448
449 /* ... */
450
451 /* profit! */
452
453 cleanup:
454 if (fd >= 0) {
455 close(fd);
456 }
457 if (ctlfd >= 0) {
458 close(ctlfd);
459 }
460 while ((acl_rule = QSIMPLEQ_FIRST(&acl_list)) != NULL) {
461 QSIMPLEQ_REMOVE_HEAD(&acl_list, entry);
462 g_free(acl_rule);
463 }
464
465 return ret;
466 }
467