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
  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
  52 enum {
  53     ACL_ALLOW = 0,
  54     ACL_ALLOW_ALL,
  55     ACL_DENY,
  56     ACL_DENY_ALL,
  57 };
  58
  59 typedef struct ACLRule {
  60     int type;
  61     char iface[IFNAMSIZ];
  62     QSIMPLEQ_ENTRY(ACLRule) entry;
  63 } ACLRule;
  64
  65 typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;
  66
  67 static void usage(void)
  68 {
  69     fprintf(stderr,
  70             "Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
  71 }
  72
  73 static 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 (g_ascii_isspace(*ptr)) {
  89             ptr++;
  90         }
  91
  92         /* skip comments and empty lines */
  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 (g_ascii_isspace(*arg)) {
 113             arg++;
 114         }
 115
 116         argend = arg + strlen(arg);
 117         while (arg != argend && g_ascii_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             /* ignore errors */
 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
 156 static 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
 171 static 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
 177 static 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
 205 static int drop_privileges(void)
 206 {
 207     /* clear all capabilities */
 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     /* change to calling user's real uid and gid, retaining supplemental
 216      * groups and CAP_NET_ADMIN */
 217     if (capng_change_id(getuid(), getgid(), CAPNG_CLEAR_BOUNDING)) {
 218         return -1;
 219     }
 220
 221     return 0;
 222 }
 223 #endif
 224
 225 int 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 = -1, ctlfd = -1, 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     /* if we're run from an suid binary, immediately drop privileges preserving
 245      * cap_net_admin */
 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     /* parse arguments */
 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     /* parse default acl file */
 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     /* validate bridge against acl -- default policy is to deny
 283      * according acl policy if we have a deny and allow both
 284      * then deny should always win over allow
 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     /* open a socket to use to control the network interfaces */
 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     /* open the tap device */
 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     /* request a tap device, disable PI, and add vnet header support if
 332      * requested and it's available. */
 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     /* save tap device name */
 346     snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);
 347
 348     /* get the mtu of the bridge */
 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     /* save mtu */
 358     mtu = ifr.ifr_mtu;
 359
 360     /* set the mtu of the interface based on the bridge */
 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     /* Linux uses the lowest enslaved MAC address as the MAC address of
 371      * the bridge.  Set MAC address to a high value so that it doesn't
 372      * affect the MAC address of the bridge.
 373      */
 374     if (ioctl(ctlfd, SIOCGIFHWADDR, &ifr) < 0) {
 375         fprintf(stderr, "failed to get MAC address of device `%s': %s\n",
 376                 iface, strerror(errno));
 377         ret = EXIT_FAILURE;
 378         goto cleanup;
 379     }
 380     ifr.ifr_hwaddr.sa_data[0] = 0xFE;
 381     if (ioctl(ctlfd, SIOCSIFHWADDR, &ifr) < 0) {
 382         fprintf(stderr, "failed to set MAC address of device `%s': %s\n",
 383                 iface, strerror(errno));
 384         ret = EXIT_FAILURE;
 385         goto cleanup;
 386     }
 387
 388     /* add the interface to the bridge */
 389     prep_ifreq(&ifr, bridge);
 390     ifindex = if_nametoindex(iface);
 391 #ifndef SIOCBRADDIF
 392     ifargs[0] = BRCTL_ADD_IF;
 393     ifargs[1] = ifindex;
 394     ifargs[2] = 0;
 395     ifargs[3] = 0;
 396     ifr.ifr_data = (void *)ifargs;
 397     ret = ioctl(ctlfd, SIOCDEVPRIVATE, &ifr);
 398 #else
 399     ifr.ifr_ifindex = ifindex;
 400     ret = ioctl(ctlfd, SIOCBRADDIF, &ifr);
 401 #endif
 402     if (ret == -1) {
 403         fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
 404                 iface, bridge, strerror(errno));
 405         ret = EXIT_FAILURE;
 406         goto cleanup;
 407     }
 408
 409     /* bring the interface up */
 410     prep_ifreq(&ifr, iface);
 411     if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
 412         fprintf(stderr, "failed to get interface flags for `%s': %s\n",
 413                 iface, strerror(errno));
 414         ret = EXIT_FAILURE;
 415         goto cleanup;
 416     }
 417
 418     ifr.ifr_flags |= IFF_UP;
 419     if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
 420         fprintf(stderr, "failed to bring up interface `%s': %s\n",
 421                 iface, strerror(errno));
 422         ret = EXIT_FAILURE;
 423         goto cleanup;
 424     }
 425
 426     /* write fd to the domain socket */
 427     if (send_fd(unixfd, fd) == -1) {
 428         fprintf(stderr, "failed to write fd to unix socket: %s\n",
 429                 strerror(errno));
 430         ret = EXIT_FAILURE;
 431         goto cleanup;
 432     }
 433
 434     /* ... */
 435
 436     /* profit! */
 437
 438 cleanup:
 439     if (fd >= 0) {
 440         close(fd);
 441     }
 442     if (ctlfd >= 0) {
 443         close(ctlfd);
 444     }
 445     while ((acl_rule = QSIMPLEQ_FIRST(&acl_list)) != NULL) {
 446         QSIMPLEQ_REMOVE_HEAD(&acl_list, entry);
 447         g_free(acl_rule);
 448     }
 449
 450     return ret;
 451 }