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 #include "qemu/osdep.h"
  17
  18
  19 #include <sys/ioctl.h>
  20 #include <sys/socket.h>
  21 #include <sys/un.h>
  22 #include <sys/prctl.h>
  23
  24 #include <net/if.h>
  25
  26 #include <linux/sockios.h>
  27
  28 #ifndef SIOCBRADDIF
  29 #include <linux/if_bridge.h>
  30 #endif
  31
  32 #include "qemu/queue.h"
  33
  34 #include "net/tap-linux.h"
  35
  36 #ifdef CONFIG_LIBCAP
  37 #include <cap-ng.h>
  38 #endif
  39
  40 #define DEFAULT_ACL_FILE CONFIG_QEMU_CONFDIR "/bridge.conf"
  41
  42 enum {
  43     ACL_ALLOW = 0,
  44     ACL_ALLOW_ALL,
  45     ACL_DENY,
  46     ACL_DENY_ALL,
  47 };
  48
  49 typedef struct ACLRule {
  50     int type;
  51     char iface[IFNAMSIZ];
  52     QSIMPLEQ_ENTRY(ACLRule) entry;
  53 } ACLRule;
  54
  55 typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;
  56
  57 static void usage(void)
  58 {
  59     fprintf(stderr,
  60             "Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
  61 }
  62
  63 static int parse_acl_file(const char *filename, ACLList *acl_list)
  64 {
  65     FILE *f;
  66     char line[4096];
  67     ACLRule *acl_rule;
  68
  69     f = fopen(filename, "r");
  70     if (f == NULL) {
  71         return -1;
  72     }
  73
  74     while (fgets(line, sizeof(line), f) != NULL) {
  75         char *ptr = line;
  76         char *cmd, *arg, *argend;
  77
  78         while (isspace(*ptr)) {
  79             ptr++;
  80         }
  81
  82         /* skip comments and empty lines */
  83         if (*ptr == '#' || *ptr == 0) {
  84             continue;
  85         }
  86
  87         cmd = ptr;
  88         arg = strchr(cmd, ' ');
  89         if (arg == NULL) {
  90             arg = strchr(cmd, '\t');
  91         }
  92
  93         if (arg == NULL) {
  94             fprintf(stderr, "Invalid config line:\n  %s\n", line);
  95             fclose(f);
  96             errno = EINVAL;
  97             return -1;
  98         }
  99
 100         *arg = 0;
 101         arg++;
 102         while (isspace(*arg)) {
 103             arg++;
 104         }
 105
 106         argend = arg + strlen(arg);
 107         while (arg != argend && isspace(*(argend - 1))) {
 108             argend--;
 109         }
 110         *argend = 0;
 111
 112         if (strcmp(cmd, "deny") == 0) {
 113             acl_rule = g_malloc(sizeof(*acl_rule));
 114             if (strcmp(arg, "all") == 0) {
 115                 acl_rule->type = ACL_DENY_ALL;
 116             } else {
 117                 acl_rule->type = ACL_DENY;
 118                 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
 119             }
 120             QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
 121         } else if (strcmp(cmd, "allow") == 0) {
 122             acl_rule = g_malloc(sizeof(*acl_rule));
 123             if (strcmp(arg, "all") == 0) {
 124                 acl_rule->type = ACL_ALLOW_ALL;
 125             } else {
 126                 acl_rule->type = ACL_ALLOW;
 127                 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
 128             }
 129             QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
 130         } else if (strcmp(cmd, "include") == 0) {
 131             /* ignore errors */
 132             parse_acl_file(arg, acl_list);
 133         } else {
 134             fprintf(stderr, "Unknown command `%s'\n", cmd);
 135             fclose(f);
 136             errno = EINVAL;
 137             return -1;
 138         }
 139     }
 140
 141     fclose(f);
 142
 143     return 0;
 144 }
 145
 146 static bool has_vnet_hdr(int fd)
 147 {
 148     unsigned int features = 0;
 149
 150     if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
 151         return false;
 152     }
 153
 154     if (!(features & IFF_VNET_HDR)) {
 155         return false;
 156     }
 157
 158     return true;
 159 }
 160
 161 static void prep_ifreq(struct ifreq *ifr, const char *ifname)
 162 {
 163     memset(ifr, 0, sizeof(*ifr));
 164     snprintf(ifr->ifr_name, IFNAMSIZ, "%s", ifname);
 165 }
 166
 167 static int send_fd(int c, int fd)
 168 {
 169     char msgbuf[CMSG_SPACE(sizeof(fd))];
 170     struct msghdr msg = {
 171         .msg_control = msgbuf,
 172         .msg_controllen = sizeof(msgbuf),
 173     };
 174     struct cmsghdr *cmsg;
 175     struct iovec iov;
 176     char req[1] = { 0x00 };
 177
 178     cmsg = CMSG_FIRSTHDR(&msg);
 179     cmsg->cmsg_level = SOL_SOCKET;
 180     cmsg->cmsg_type = SCM_RIGHTS;
 181     cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
 182     msg.msg_controllen = cmsg->cmsg_len;
 183
 184     iov.iov_base = req;
 185     iov.iov_len = sizeof(req);
 186
 187     msg.msg_iov = &iov;
 188     msg.msg_iovlen = 1;
 189     memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
 190
 191     return sendmsg(c, &msg, 0);
 192 }
 193
 194 #ifdef CONFIG_LIBCAP
 195 static int drop_privileges(void)
 196 {
 197     /* clear all capabilities */
 198     capng_clear(CAPNG_SELECT_BOTH);
 199
 200     if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE | CAPNG_PERMITTED,
 201                      CAP_NET_ADMIN) < 0) {
 202         return -1;
 203     }
 204
 205     /* change to calling user's real uid and gid, retaining supplemental
 206      * groups and CAP_NET_ADMIN */
 207     if (capng_change_id(getuid(), getgid(), CAPNG_CLEAR_BOUNDING)) {
 208         return -1;
 209     }
 210
 211     return 0;
 212 }
 213 #endif
 214
 215 int main(int argc, char **argv)
 216 {
 217     struct ifreq ifr;
 218 #ifndef SIOCBRADDIF
 219     unsigned long ifargs[4];
 220 #endif
 221     int ifindex;
 222     int fd = -1, ctlfd = -1, unixfd = -1;
 223     int use_vnet = 0;
 224     int mtu;
 225     const char *bridge = NULL;
 226     char iface[IFNAMSIZ];
 227     int index;
 228     ACLRule *acl_rule;
 229     ACLList acl_list;
 230     int access_allowed, access_denied;
 231     int ret = EXIT_SUCCESS;
 232
 233 #ifdef CONFIG_LIBCAP
 234     /* if we're run from an suid binary, immediately drop privileges preserving
 235      * cap_net_admin */
 236     if (geteuid() == 0 && getuid() != geteuid()) {
 237         if (drop_privileges() == -1) {
 238             fprintf(stderr, "failed to drop privileges\n");
 239             return 1;
 240         }
 241     }
 242 #endif
 243
 244     /* parse arguments */
 245     for (index = 1; index < argc; index++) {
 246         if (strcmp(argv[index], "--use-vnet") == 0) {
 247             use_vnet = 1;
 248         } else if (strncmp(argv[index], "--br=", 5) == 0) {
 249             bridge = &argv[index][5];
 250         } else if (strncmp(argv[index], "--fd=", 5) == 0) {
 251             unixfd = atoi(&argv[index][5]);
 252         } else {
 253             usage();
 254             return EXIT_FAILURE;
 255         }
 256     }
 257
 258     if (bridge == NULL || unixfd == -1) {
 259         usage();
 260         return EXIT_FAILURE;
 261     }
 262
 263     /* parse default acl file */
 264     QSIMPLEQ_INIT(&acl_list);
 265     if (parse_acl_file(DEFAULT_ACL_FILE, &acl_list) == -1) {
 266         fprintf(stderr, "failed to parse default acl file `%s'\n",
 267                 DEFAULT_ACL_FILE);
 268         ret = EXIT_FAILURE;
 269         goto cleanup;
 270     }
 271
 272     /* validate bridge against acl -- default policy is to deny
 273      * according acl policy if we have a deny and allow both
 274      * then deny should always win over allow
 275      */
 276     access_allowed = 0;
 277     access_denied = 0;
 278     QSIMPLEQ_FOREACH(acl_rule, &acl_list, entry) {
 279         switch (acl_rule->type) {
 280         case ACL_ALLOW_ALL:
 281             access_allowed = 1;
 282             break;
 283         case ACL_ALLOW:
 284             if (strcmp(bridge, acl_rule->iface) == 0) {
 285                 access_allowed = 1;
 286             }
 287             break;
 288         case ACL_DENY_ALL:
 289             access_denied = 1;
 290             break;
 291         case ACL_DENY:
 292             if (strcmp(bridge, acl_rule->iface) == 0) {
 293                 access_denied = 1;
 294             }
 295             break;
 296         }
 297     }
 298
 299     if ((access_allowed == 0) || (access_denied == 1)) {
 300         fprintf(stderr, "access denied by acl file\n");
 301         ret = EXIT_FAILURE;
 302         goto cleanup;
 303     }
 304
 305     /* open a socket to use to control the network interfaces */
 306     ctlfd = socket(AF_INET, SOCK_STREAM, 0);
 307     if (ctlfd == -1) {
 308         fprintf(stderr, "failed to open control socket: %s\n", strerror(errno));
 309         ret = EXIT_FAILURE;
 310         goto cleanup;
 311     }
 312
 313     /* open the tap device */
 314     fd = open("/dev/net/tun", O_RDWR);
 315     if (fd == -1) {
 316         fprintf(stderr, "failed to open /dev/net/tun: %s\n", strerror(errno));
 317         ret = EXIT_FAILURE;
 318         goto cleanup;
 319     }
 320
 321     /* request a tap device, disable PI, and add vnet header support if
 322      * requested and it's available. */
 323     prep_ifreq(&ifr, "tap%d");
 324     ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
 325     if (use_vnet && has_vnet_hdr(fd)) {
 326         ifr.ifr_flags |= IFF_VNET_HDR;
 327     }
 328
 329     if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
 330         fprintf(stderr, "failed to create tun device: %s\n", strerror(errno));
 331         ret = EXIT_FAILURE;
 332         goto cleanup;
 333     }
 334
 335     /* save tap device name */
 336     snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);
 337
 338     /* get the mtu of the bridge */
 339     prep_ifreq(&ifr, bridge);
 340     if (ioctl(ctlfd, SIOCGIFMTU, &ifr) == -1) {
 341         fprintf(stderr, "failed to get mtu of bridge `%s': %s\n",
 342                 bridge, strerror(errno));
 343         ret = EXIT_FAILURE;
 344         goto cleanup;
 345     }
 346
 347     /* save mtu */
 348     mtu = ifr.ifr_mtu;
 349
 350     /* set the mtu of the interface based on the bridge */
 351     prep_ifreq(&ifr, iface);
 352     ifr.ifr_mtu = mtu;
 353     if (ioctl(ctlfd, SIOCSIFMTU, &ifr) == -1) {
 354         fprintf(stderr, "failed to set mtu of device `%s' to %d: %s\n",
 355                 iface, mtu, strerror(errno));
 356         ret = EXIT_FAILURE;
 357         goto cleanup;
 358     }
 359
 360     /* Linux uses the lowest enslaved MAC address as the MAC address of
 361      * the bridge.  Set MAC address to a high value so that it doesn't
 362      * affect the MAC address of the bridge.
 363      */
 364     if (ioctl(ctlfd, SIOCGIFHWADDR, &ifr) < 0) {
 365         fprintf(stderr, "failed to get MAC address of device `%s': %s\n",
 366                 iface, strerror(errno));
 367         ret = EXIT_FAILURE;
 368         goto cleanup;
 369     }
 370     ifr.ifr_hwaddr.sa_data[0] = 0xFE;
 371     if (ioctl(ctlfd, SIOCSIFHWADDR, &ifr) < 0) {
 372         fprintf(stderr, "failed to set MAC address of device `%s': %s\n",
 373                 iface, strerror(errno));
 374         ret = EXIT_FAILURE;
 375         goto cleanup;
 376     }
 377
 378     /* add the interface to the bridge */
 379     prep_ifreq(&ifr, bridge);
 380     ifindex = if_nametoindex(iface);
 381 #ifndef SIOCBRADDIF
 382     ifargs[0] = BRCTL_ADD_IF;
 383     ifargs[1] = ifindex;
 384     ifargs[2] = 0;
 385     ifargs[3] = 0;
 386     ifr.ifr_data = (void *)ifargs;
 387     ret = ioctl(ctlfd, SIOCDEVPRIVATE, &ifr);
 388 #else
 389     ifr.ifr_ifindex = ifindex;
 390     ret = ioctl(ctlfd, SIOCBRADDIF, &ifr);
 391 #endif
 392     if (ret == -1) {
 393         fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
 394                 iface, bridge, strerror(errno));
 395         ret = EXIT_FAILURE;
 396         goto cleanup;
 397     }
 398
 399     /* bring the interface up */
 400     prep_ifreq(&ifr, iface);
 401     if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
 402         fprintf(stderr, "failed to get interface flags for `%s': %s\n",
 403                 iface, strerror(errno));
 404         ret = EXIT_FAILURE;
 405         goto cleanup;
 406     }
 407
 408     ifr.ifr_flags |= IFF_UP;
 409     if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
 410         fprintf(stderr, "failed to bring up interface `%s': %s\n",
 411                 iface, strerror(errno));
 412         ret = EXIT_FAILURE;
 413         goto cleanup;
 414     }
 415
 416     /* write fd to the domain socket */
 417     if (send_fd(unixfd, fd) == -1) {
 418         fprintf(stderr, "failed to write fd to unix socket: %s\n",
 419                 strerror(errno));
 420         ret = EXIT_FAILURE;
 421         goto cleanup;
 422     }
 423
 424     /* ... */
 425
 426     /* profit! */
 427
 428 cleanup:
 429     if (fd >= 0) {
 430         close(fd);
 431     }
 432     if (ctlfd >= 0) {
 433         close(ctlfd);
 434     }
 435     while ((acl_rule = QSIMPLEQ_FIRST(&acl_list)) != NULL) {
 436         QSIMPLEQ_REMOVE_HEAD(&acl_list, entry);
 437         g_free(acl_rule);
 438     }
 439
 440     return ret;
 441 }