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  * 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 }