1
2
3
4
5
6
7
8
9
10
11
12
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#ifndef SIOCBRADDIF
39#include <linux/if_bridge.h>
40#endif
41
42#include "qemu-queue.h"
43
44#include "net/tap-linux.h"
45
46#ifdef CONFIG_LIBCAP
47#include <cap-ng.h>
48#endif
49
50#define DEFAULT_ACL_FILE CONFIG_QEMU_CONFDIR "/bridge.conf"
51
52enum {
53 ACL_ALLOW = 0,
54 ACL_ALLOW_ALL,
55 ACL_DENY,
56 ACL_DENY_ALL,
57};
58
59typedef struct ACLRule {
60 int type;
61 char iface[IFNAMSIZ];
62 QSIMPLEQ_ENTRY(ACLRule) entry;
63} ACLRule;
64
65typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;
66
67static void usage(void)
68{
69 fprintf(stderr,
70 "Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
71}
72
73static int parse_acl_file(const char *filename, ACLList *acl_list)
74{
75 FILE *f;
76 char line[4096];
77 ACLRule *acl_rule;
78
79 f = fopen(filename, "r");
80 if (f == NULL) {
81 return -1;
82 }
83
84 while (fgets(line, sizeof(line), f) != NULL) {
85 char *ptr = line;
86 char *cmd, *arg, *argend;
87
88 while (isspace(*ptr)) {
89 ptr++;
90 }
91
92
93 if (*ptr == '#' || *ptr == 0) {
94 continue;
95 }
96
97 cmd = ptr;
98 arg = strchr(cmd, ' ');
99 if (arg == NULL) {
100 arg = strchr(cmd, '\t');
101 }
102
103 if (arg == NULL) {
104 fprintf(stderr, "Invalid config line:\n %s\n", line);
105 fclose(f);
106 errno = EINVAL;
107 return -1;
108 }
109
110 *arg = 0;
111 arg++;
112 while (isspace(*arg)) {
113 arg++;
114 }
115
116 argend = arg + strlen(arg);
117 while (arg != argend && isspace(*(argend - 1))) {
118 argend--;
119 }
120 *argend = 0;
121
122 if (strcmp(cmd, "deny") == 0) {
123 acl_rule = g_malloc(sizeof(*acl_rule));
124 if (strcmp(arg, "all") == 0) {
125 acl_rule->type = ACL_DENY_ALL;
126 } else {
127 acl_rule->type = ACL_DENY;
128 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
129 }
130 QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
131 } else if (strcmp(cmd, "allow") == 0) {
132 acl_rule = g_malloc(sizeof(*acl_rule));
133 if (strcmp(arg, "all") == 0) {
134 acl_rule->type = ACL_ALLOW_ALL;
135 } else {
136 acl_rule->type = ACL_ALLOW;
137 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
138 }
139 QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
140 } else if (strcmp(cmd, "include") == 0) {
141
142 parse_acl_file(arg, acl_list);
143 } else {
144 fprintf(stderr, "Unknown command `%s'\n", cmd);
145 fclose(f);
146 errno = EINVAL;
147 return -1;
148 }
149 }
150
151 fclose(f);
152
153 return 0;
154}
155
156static bool has_vnet_hdr(int fd)
157{
158 unsigned int features = 0;
159
160 if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
161 return false;
162 }
163
164 if (!(features & IFF_VNET_HDR)) {
165 return false;
166 }
167
168 return true;
169}
170
171static void prep_ifreq(struct ifreq *ifr, const char *ifname)
172{
173 memset(ifr, 0, sizeof(*ifr));
174 snprintf(ifr->ifr_name, IFNAMSIZ, "%s", ifname);
175}
176
177static int send_fd(int c, int fd)
178{
179 char msgbuf[CMSG_SPACE(sizeof(fd))];
180 struct msghdr msg = {
181 .msg_control = msgbuf,
182 .msg_controllen = sizeof(msgbuf),
183 };
184 struct cmsghdr *cmsg;
185 struct iovec iov;
186 char req[1] = { 0x00 };
187
188 cmsg = CMSG_FIRSTHDR(&msg);
189 cmsg->cmsg_level = SOL_SOCKET;
190 cmsg->cmsg_type = SCM_RIGHTS;
191 cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
192 msg.msg_controllen = cmsg->cmsg_len;
193
194 iov.iov_base = req;
195 iov.iov_len = sizeof(req);
196
197 msg.msg_iov = &iov;
198 msg.msg_iovlen = 1;
199 memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
200
201 return sendmsg(c, &msg, 0);
202}
203
204#ifdef CONFIG_LIBCAP
205static int drop_privileges(void)
206{
207
208 capng_clear(CAPNG_SELECT_BOTH);
209
210 if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE | CAPNG_PERMITTED,
211 CAP_NET_ADMIN) < 0) {
212 return -1;
213 }
214
215
216
217 if (capng_change_id(getuid(), getgid(), CAPNG_CLEAR_BOUNDING)) {
218 return -1;
219 }
220
221 return 0;
222}
223#endif
224
225int main(int argc, char **argv)
226{
227 struct ifreq ifr;
228#ifndef SIOCBRADDIF
229 unsigned long ifargs[4];
230#endif
231 int ifindex;
232 int fd, ctlfd, unixfd = -1;
233 int use_vnet = 0;
234 int mtu;
235 const char *bridge = NULL;
236 char iface[IFNAMSIZ];
237 int index;
238 ACLRule *acl_rule;
239 ACLList acl_list;
240 int access_allowed, access_denied;
241 int ret = EXIT_SUCCESS;
242
243#ifdef CONFIG_LIBCAP
244
245
246 if (geteuid() == 0 && getuid() != geteuid()) {
247 if (drop_privileges() == -1) {
248 fprintf(stderr, "failed to drop privileges\n");
249 return 1;
250 }
251 }
252#endif
253
254
255 for (index = 1; index < argc; index++) {
256 if (strcmp(argv[index], "--use-vnet") == 0) {
257 use_vnet = 1;
258 } else if (strncmp(argv[index], "--br=", 5) == 0) {
259 bridge = &argv[index][5];
260 } else if (strncmp(argv[index], "--fd=", 5) == 0) {
261 unixfd = atoi(&argv[index][5]);
262 } else {
263 usage();
264 return EXIT_FAILURE;
265 }
266 }
267
268 if (bridge == NULL || unixfd == -1) {
269 usage();
270 return EXIT_FAILURE;
271 }
272
273
274 QSIMPLEQ_INIT(&acl_list);
275 if (parse_acl_file(DEFAULT_ACL_FILE, &acl_list) == -1) {
276 fprintf(stderr, "failed to parse default acl file `%s'\n",
277 DEFAULT_ACL_FILE);
278 ret = EXIT_FAILURE;
279 goto cleanup;
280 }
281
282
283
284
285
286 access_allowed = 0;
287 access_denied = 0;
288 QSIMPLEQ_FOREACH(acl_rule, &acl_list, entry) {
289 switch (acl_rule->type) {
290 case ACL_ALLOW_ALL:
291 access_allowed = 1;
292 break;
293 case ACL_ALLOW:
294 if (strcmp(bridge, acl_rule->iface) == 0) {
295 access_allowed = 1;
296 }
297 break;
298 case ACL_DENY_ALL:
299 access_denied = 1;
300 break;
301 case ACL_DENY:
302 if (strcmp(bridge, acl_rule->iface) == 0) {
303 access_denied = 1;
304 }
305 break;
306 }
307 }
308
309 if ((access_allowed == 0) || (access_denied == 1)) {
310 fprintf(stderr, "access denied by acl file\n");
311 ret = EXIT_FAILURE;
312 goto cleanup;
313 }
314
315
316 ctlfd = socket(AF_INET, SOCK_STREAM, 0);
317 if (ctlfd == -1) {
318 fprintf(stderr, "failed to open control socket: %s\n", strerror(errno));
319 ret = EXIT_FAILURE;
320 goto cleanup;
321 }
322
323
324 fd = open("/dev/net/tun", O_RDWR);
325 if (fd == -1) {
326 fprintf(stderr, "failed to open /dev/net/tun: %s\n", strerror(errno));
327 ret = EXIT_FAILURE;
328 goto cleanup;
329 }
330
331
332
333 prep_ifreq(&ifr, "tap%d");
334 ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
335 if (use_vnet && has_vnet_hdr(fd)) {
336 ifr.ifr_flags |= IFF_VNET_HDR;
337 }
338
339 if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
340 fprintf(stderr, "failed to create tun device: %s\n", strerror(errno));
341 ret = EXIT_FAILURE;
342 goto cleanup;
343 }
344
345
346 snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);
347
348
349 prep_ifreq(&ifr, bridge);
350 if (ioctl(ctlfd, SIOCGIFMTU, &ifr) == -1) {
351 fprintf(stderr, "failed to get mtu of bridge `%s': %s\n",
352 bridge, strerror(errno));
353 ret = EXIT_FAILURE;
354 goto cleanup;
355 }
356
357
358 mtu = ifr.ifr_mtu;
359
360
361 prep_ifreq(&ifr, iface);
362 ifr.ifr_mtu = mtu;
363 if (ioctl(ctlfd, SIOCSIFMTU, &ifr) == -1) {
364 fprintf(stderr, "failed to set mtu of device `%s' to %d: %s\n",
365 iface, mtu, strerror(errno));
366 ret = EXIT_FAILURE;
367 goto cleanup;
368 }
369
370
371 prep_ifreq(&ifr, bridge);
372 ifindex = if_nametoindex(iface);
373#ifndef SIOCBRADDIF
374 ifargs[0] = BRCTL_ADD_IF;
375 ifargs[1] = ifindex;
376 ifargs[2] = 0;
377 ifargs[3] = 0;
378 ifr.ifr_data = (void *)ifargs;
379 ret = ioctl(ctlfd, SIOCDEVPRIVATE, &ifr);
380#else
381 ifr.ifr_ifindex = ifindex;
382 ret = ioctl(ctlfd, SIOCBRADDIF, &ifr);
383#endif
384 if (ret == -1) {
385 fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
386 iface, bridge, strerror(errno));
387 ret = EXIT_FAILURE;
388 goto cleanup;
389 }
390
391
392 prep_ifreq(&ifr, iface);
393 if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
394 fprintf(stderr, "failed to get interface flags for `%s': %s\n",
395 iface, strerror(errno));
396 ret = EXIT_FAILURE;
397 goto cleanup;
398 }
399
400 ifr.ifr_flags |= IFF_UP;
401 if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
402 fprintf(stderr, "failed to bring up interface `%s': %s\n",
403 iface, strerror(errno));
404 ret = EXIT_FAILURE;
405 goto cleanup;
406 }
407
408
409 if (send_fd(unixfd, fd) == -1) {
410 fprintf(stderr, "failed to write fd to unix socket: %s\n",
411 strerror(errno));
412 ret = EXIT_FAILURE;
413 goto cleanup;
414 }
415
416
417
418
419
420cleanup:
421
422 while ((acl_rule = QSIMPLEQ_FIRST(&acl_list)) != NULL) {
423 QSIMPLEQ_REMOVE_HEAD(&acl_list, entry);
424 g_free(acl_rule);
425 }
426
427 return ret;
428}
429
