xref: /openbmc/qemu/qemu-bridge-helper.c (revision b14df228) 
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 
68 static void usage(void)
69 {
70     fprintf(stderr,
71             "Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
72 }
73 
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 
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 
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 
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
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 
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