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 #include <glib.h>
  19
  20 #include <sys/ioctl.h>
  21 #include <sys/socket.h>
  22 #include <sys/un.h>
  23 #include <sys/prctl.h>
  24
  25 #include <net/if.h>
  26
  27 #include <linux/sockios.h>
  28
  29 #ifndef SIOCBRADDIF
  30 #include <linux/if_bridge.h>
  31 #endif
  32
  33 #include "qemu/queue.h"
  34
  35 #include "net/tap-linux.h"
  36
  37 #ifdef CONFIG_LIBCAP
  38 #include <cap-ng.h>
  39 #endif
  40
  41 #define DEFAULT_ACL_FILE CONFIG_QEMU_CONFDIR "/bridge.conf"
  42
  43 enum {
  44     ACL_ALLOW = 0,
  45     ACL_ALLOW_ALL,
  46     ACL_DENY,
  47     ACL_DENY_ALL,
  48 };
  49
  50 typedef struct ACLRule {
  51     int type;
  52     char iface[IFNAMSIZ];
  53     QSIMPLEQ_ENTRY(ACLRule) entry;
  54 } ACLRule;
  55
  56 typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;
  57
  58 static void usage(void)
  59 {
  60     fprintf(stderr,
  61             "Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
  62 }
  63
  64 static int parse_acl_file(const char *filename, ACLList *acl_list)
  65 {
  66     FILE *f;
  67     char line[4096];
  68     ACLRule *acl_rule;
  69
  70     f = fopen(filename, "r");
  71     if (f == NULL) {
  72         return -1;
  73     }
  74
  75     while (fgets(line, sizeof(line), f) != NULL) {
  76         char *ptr = line;
  77         char *cmd, *arg, *argend;
  78
  79         while (isspace(*ptr)) {
  80             ptr++;
  81         }
  82
  83         /* skip comments and empty lines */
  84         if (*ptr == '#' || *ptr == 0) {
  85             continue;
  86         }
  87
  88         cmd = ptr;
  89         arg = strchr(cmd, ' ');
  90         if (arg == NULL) {
  91             arg = strchr(cmd, '\t');
  92         }
  93
  94         if (arg == NULL) {
  95             fprintf(stderr, "Invalid config line:\n  %s\n", line);
  96             fclose(f);
  97             errno = EINVAL;
  98             return -1;
  99         }
 100
 101         *arg = 0;
 102         arg++;
 103         while (isspace(*arg)) {
 104             arg++;
 105         }
 106
 107         argend = arg + strlen(arg);
 108         while (arg != argend && isspace(*(argend - 1))) {
 109             argend--;
 110         }
 111         *argend = 0;
 112
 113         if (strcmp(cmd, "deny") == 0) {
 114             acl_rule = g_malloc(sizeof(*acl_rule));
 115             if (strcmp(arg, "all") == 0) {
 116                 acl_rule->type = ACL_DENY_ALL;
 117             } else {
 118                 acl_rule->type = ACL_DENY;
 119                 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
 120             }
 121             QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
 122         } else if (strcmp(cmd, "allow") == 0) {
 123             acl_rule = g_malloc(sizeof(*acl_rule));
 124             if (strcmp(arg, "all") == 0) {
 125                 acl_rule->type = ACL_ALLOW_ALL;
 126             } else {
 127                 acl_rule->type = ACL_ALLOW;
 128                 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
 129             }
 130             QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
 131         } else if (strcmp(cmd, "include") == 0) {
 132             /* ignore errors */
 133             parse_acl_file(arg, acl_list);
 134         } else {
 135             fprintf(stderr, "Unknown command `%s'\n", cmd);
 136             fclose(f);
 137             errno = EINVAL;
 138             return -1;
 139         }
 140     }
 141
 142     fclose(f);
 143
 144     return 0;
 145 }
 146
 147 static bool has_vnet_hdr(int fd)
 148 {
 149     unsigned int features = 0;
 150
 151     if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
 152         return false;
 153     }
 154
 155     if (!(features & IFF_VNET_HDR)) {
 156         return false;
 157     }
 158
 159     return true;
 160 }
 161
 162 static void prep_ifreq(struct ifreq *ifr, const char *ifname)
 163 {
 164     memset(ifr, 0, sizeof(*ifr));
 165     snprintf(ifr->ifr_name, IFNAMSIZ, "%s", ifname);
 166 }
 167
 168 static int send_fd(int c, int fd)
 169 {
 170     char msgbuf[CMSG_SPACE(sizeof(fd))];
 171     struct msghdr msg = {
 172         .msg_control = msgbuf,
 173         .msg_controllen = sizeof(msgbuf),
 174     };
 175     struct cmsghdr *cmsg;
 176     struct iovec iov;
 177     char req[1] = { 0x00 };
 178
 179     cmsg = CMSG_FIRSTHDR(&msg);
 180     cmsg->cmsg_level = SOL_SOCKET;
 181     cmsg->cmsg_type = SCM_RIGHTS;
 182     cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
 183     msg.msg_controllen = cmsg->cmsg_len;
 184
 185     iov.iov_base = req;
 186     iov.iov_len = sizeof(req);
 187
 188     msg.msg_iov = &iov;
 189     msg.msg_iovlen = 1;
 190     memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
 191
 192     return sendmsg(c, &msg, 0);
 193 }
 194
 195 #ifdef CONFIG_LIBCAP
 196 static int drop_privileges(void)
 197 {
 198     /* clear all capabilities */
 199     capng_clear(CAPNG_SELECT_BOTH);
 200
 201     if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE | CAPNG_PERMITTED,
 202                      CAP_NET_ADMIN) < 0) {
 203         return -1;
 204     }
 205
 206     /* change to calling user's real uid and gid, retaining supplemental
 207      * groups and CAP_NET_ADMIN */
 208     if (capng_change_id(getuid(), getgid(), CAPNG_CLEAR_BOUNDING)) {
 209         return -1;
 210     }
 211
 212     return 0;
 213 }
 214 #endif
 215
 216 int main(int argc, char **argv)
 217 {
 218     struct ifreq ifr;
 219 #ifndef SIOCBRADDIF
 220     unsigned long ifargs[4];
 221 #endif
 222     int ifindex;
 223     int fd = -1, ctlfd = -1, unixfd = -1;
 224     int use_vnet = 0;
 225     int mtu;
 226     const char *bridge = NULL;
 227     char iface[IFNAMSIZ];
 228     int index;
 229     ACLRule *acl_rule;
 230     ACLList acl_list;
 231     int access_allowed, access_denied;
 232     int ret = EXIT_SUCCESS;
 233
 234 #ifdef CONFIG_LIBCAP
 235     /* if we're run from an suid binary, immediately drop privileges preserving
 236      * cap_net_admin */
 237     if (geteuid() == 0 && getuid() != geteuid()) {
 238         if (drop_privileges() == -1) {
 239             fprintf(stderr, "failed to drop privileges\n");
 240             return 1;
 241         }
 242     }
 243 #endif
 244
 245     /* parse arguments */
 246     for (index = 1; index < argc; index++) {
 247         if (strcmp(argv[index], "--use-vnet") == 0) {
 248             use_vnet = 1;
 249         } else if (strncmp(argv[index], "--br=", 5) == 0) {
 250             bridge = &argv[index][5];
 251         } else if (strncmp(argv[index], "--fd=", 5) == 0) {
 252             unixfd = atoi(&argv[index][5]);
 253         } else {
 254             usage();
 255             return EXIT_FAILURE;
 256         }
 257     }
 258
 259     if (bridge == NULL || unixfd == -1) {
 260         usage();
 261         return EXIT_FAILURE;
 262     }
 263
 264     /* parse default acl file */
 265     QSIMPLEQ_INIT(&acl_list);
 266     if (parse_acl_file(DEFAULT_ACL_FILE, &acl_list) == -1) {
 267         fprintf(stderr, "failed to parse default acl file `%s'\n",
 268                 DEFAULT_ACL_FILE);
 269         ret = EXIT_FAILURE;
 270         goto cleanup;
 271     }
 272
 273     /* validate bridge against acl -- default policy is to deny
 274      * according acl policy if we have a deny and allow both
 275      * then deny should always win over allow
 276      */
 277     access_allowed = 0;
 278     access_denied = 0;
 279     QSIMPLEQ_FOREACH(acl_rule, &acl_list, entry) {
 280         switch (acl_rule->type) {
 281         case ACL_ALLOW_ALL:
 282             access_allowed = 1;
 283             break;
 284         case ACL_ALLOW:
 285             if (strcmp(bridge, acl_rule->iface) == 0) {
 286                 access_allowed = 1;
 287             }
 288             break;
 289         case ACL_DENY_ALL:
 290             access_denied = 1;
 291             break;
 292         case ACL_DENY:
 293             if (strcmp(bridge, acl_rule->iface) == 0) {
 294                 access_denied = 1;
 295             }
 296             break;
 297         }
 298     }
 299
 300     if ((access_allowed == 0) || (access_denied == 1)) {
 301         fprintf(stderr, "access denied by acl file\n");
 302         ret = EXIT_FAILURE;
 303         goto cleanup;
 304     }
 305
 306     /* open a socket to use to control the network interfaces */
 307     ctlfd = socket(AF_INET, SOCK_STREAM, 0);
 308     if (ctlfd == -1) {
 309         fprintf(stderr, "failed to open control socket: %s\n", strerror(errno));
 310         ret = EXIT_FAILURE;
 311         goto cleanup;
 312     }
 313
 314     /* open the tap device */
 315     fd = open("/dev/net/tun", O_RDWR);
 316     if (fd == -1) {
 317         fprintf(stderr, "failed to open /dev/net/tun: %s\n", strerror(errno));
 318         ret = EXIT_FAILURE;
 319         goto cleanup;
 320     }
 321
 322     /* request a tap device, disable PI, and add vnet header support if
 323      * requested and it's available. */
 324     prep_ifreq(&ifr, "tap%d");
 325     ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
 326     if (use_vnet && has_vnet_hdr(fd)) {
 327         ifr.ifr_flags |= IFF_VNET_HDR;
 328     }
 329
 330     if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
 331         fprintf(stderr, "failed to create tun device: %s\n", strerror(errno));
 332         ret = EXIT_FAILURE;
 333         goto cleanup;
 334     }
 335
 336     /* save tap device name */
 337     snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);
 338
 339     /* get the mtu of the bridge */
 340     prep_ifreq(&ifr, bridge);
 341     if (ioctl(ctlfd, SIOCGIFMTU, &ifr) == -1) {
 342         fprintf(stderr, "failed to get mtu of bridge `%s': %s\n",
 343                 bridge, strerror(errno));
 344         ret = EXIT_FAILURE;
 345         goto cleanup;
 346     }
 347
 348     /* save mtu */
 349     mtu = ifr.ifr_mtu;
 350
 351     /* set the mtu of the interface based on the bridge */
 352     prep_ifreq(&ifr, iface);
 353     ifr.ifr_mtu = mtu;
 354     if (ioctl(ctlfd, SIOCSIFMTU, &ifr) == -1) {
 355         fprintf(stderr, "failed to set mtu of device `%s' to %d: %s\n",
 356                 iface, mtu, strerror(errno));
 357         ret = EXIT_FAILURE;
 358         goto cleanup;
 359     }
 360
 361     /* Linux uses the lowest enslaved MAC address as the MAC address of
 362      * the bridge.  Set MAC address to a high value so that it doesn't
 363      * affect the MAC address of the bridge.
 364      */
 365     if (ioctl(ctlfd, SIOCGIFHWADDR, &ifr) < 0) {
 366         fprintf(stderr, "failed to get MAC address of device `%s': %s\n",
 367                 iface, strerror(errno));
 368         ret = EXIT_FAILURE;
 369         goto cleanup;
 370     }
 371     ifr.ifr_hwaddr.sa_data[0] = 0xFE;
 372     if (ioctl(ctlfd, SIOCSIFHWADDR, &ifr) < 0) {
 373         fprintf(stderr, "failed to set MAC address of device `%s': %s\n",
 374                 iface, strerror(errno));
 375         ret = EXIT_FAILURE;
 376         goto cleanup;
 377     }
 378
 379     /* add the interface to the bridge */
 380     prep_ifreq(&ifr, bridge);
 381     ifindex = if_nametoindex(iface);
 382 #ifndef SIOCBRADDIF
 383     ifargs[0] = BRCTL_ADD_IF;
 384     ifargs[1] = ifindex;
 385     ifargs[2] = 0;
 386     ifargs[3] = 0;
 387     ifr.ifr_data = (void *)ifargs;
 388     ret = ioctl(ctlfd, SIOCDEVPRIVATE, &ifr);
 389 #else
 390     ifr.ifr_ifindex = ifindex;
 391     ret = ioctl(ctlfd, SIOCBRADDIF, &ifr);
 392 #endif
 393     if (ret == -1) {
 394         fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
 395                 iface, bridge, strerror(errno));
 396         ret = EXIT_FAILURE;
 397         goto cleanup;
 398     }
 399
 400     /* bring the interface up */
 401     prep_ifreq(&ifr, iface);
 402     if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
 403         fprintf(stderr, "failed to get interface flags for `%s': %s\n",
 404                 iface, strerror(errno));
 405         ret = EXIT_FAILURE;
 406         goto cleanup;
 407     }
 408
 409     ifr.ifr_flags |= IFF_UP;
 410     if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
 411         fprintf(stderr, "failed to bring up interface `%s': %s\n",
 412                 iface, strerror(errno));
 413         ret = EXIT_FAILURE;
 414         goto cleanup;
 415     }
 416
 417     /* write fd to the domain socket */
 418     if (send_fd(unixfd, fd) == -1) {
 419         fprintf(stderr, "failed to write fd to unix socket: %s\n",
 420                 strerror(errno));
 421         ret = EXIT_FAILURE;
 422         goto cleanup;
 423     }
 424
 425     /* ... */
 426
 427     /* profit! */
 428
 429 cleanup:
 430     if (fd >= 0) {
 431         close(fd);
 432     }
 433     if (ctlfd >= 0) {
 434         close(ctlfd);
 435     }
 436     while ((acl_rule = QSIMPLEQ_FIRST(&acl_list)) != NULL) {
 437         QSIMPLEQ_REMOVE_HEAD(&acl_list, entry);
 438         g_free(acl_rule);
 439     }
 440
 441     return ret;
 442 }