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             goto err;
 106         }
 107
 108         *arg = 0;
 109         arg++;
 110         while (g_ascii_isspace(*arg)) {
 111             arg++;
 112         }
 113
 114         argend = arg + strlen(arg);
 115         while (arg != argend && g_ascii_isspace(*(argend - 1))) {
 116             argend--;
 117         }
 118         *argend = 0;
 119
 120         if (!g_str_equal(cmd, "include") && strlen(arg) >= IFNAMSIZ) {
 121             fprintf(stderr, "name `%s' too long: %zu\n", arg, strlen(arg));
 122             goto err;
 123         }
 124
 125         if (strcmp(cmd, "deny") == 0) {
 126             acl_rule = g_malloc(sizeof(*acl_rule));
 127             if (strcmp(arg, "all") == 0) {
 128                 acl_rule->type = ACL_DENY_ALL;
 129             } else {
 130                 acl_rule->type = ACL_DENY;
 131                 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
 132             }
 133             QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
 134         } else if (strcmp(cmd, "allow") == 0) {
 135             acl_rule = g_malloc(sizeof(*acl_rule));
 136             if (strcmp(arg, "all") == 0) {
 137                 acl_rule->type = ACL_ALLOW_ALL;
 138             } else {
 139                 acl_rule->type = ACL_ALLOW;
 140                 snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
 141             }
 142             QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
 143         } else if (strcmp(cmd, "include") == 0) {
 144             /* ignore errors */
 145             parse_acl_file(arg, acl_list);
 146         } else {
 147             fprintf(stderr, "Unknown command `%s'\n", cmd);
 148             goto err;
 149         }
 150     }
 151
 152     fclose(f);
 153     return 0;
 154
 155 err:
 156     fclose(f);
 157     errno = EINVAL;
 158     return -1;
 159
 160 }
 161
 162 static bool has_vnet_hdr(int fd)
 163 {
 164     unsigned int features = 0;
 165
 166     if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
 167         return false;
 168     }
 169
 170     if (!(features & IFF_VNET_HDR)) {
 171         return false;
 172     }
 173
 174     return true;
 175 }
 176
 177 static void prep_ifreq(struct ifreq *ifr, const char *ifname)
 178 {
 179     memset(ifr, 0, sizeof(*ifr));
 180     snprintf(ifr->ifr_name, IFNAMSIZ, "%s", ifname);
 181 }
 182
 183 static int send_fd(int c, int fd)
 184 {
 185     char msgbuf[CMSG_SPACE(sizeof(fd))];
 186     struct msghdr msg = {
 187         .msg_control = msgbuf,
 188         .msg_controllen = sizeof(msgbuf),
 189     };
 190     struct cmsghdr *cmsg;
 191     struct iovec iov;
 192     char req[1] = { 0x00 };
 193
 194     cmsg = CMSG_FIRSTHDR(&msg);
 195     cmsg->cmsg_level = SOL_SOCKET;
 196     cmsg->cmsg_type = SCM_RIGHTS;
 197     cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
 198     msg.msg_controllen = cmsg->cmsg_len;
 199
 200     iov.iov_base = req;
 201     iov.iov_len = sizeof(req);
 202
 203     msg.msg_iov = &iov;
 204     msg.msg_iovlen = 1;
 205     memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
 206
 207     return sendmsg(c, &msg, 0);
 208 }
 209
 210 #ifdef CONFIG_LIBCAP
 211 static int drop_privileges(void)
 212 {
 213     /* clear all capabilities */
 214     capng_clear(CAPNG_SELECT_BOTH);
 215
 216     if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE | CAPNG_PERMITTED,
 217                      CAP_NET_ADMIN) < 0) {
 218         return -1;
 219     }
 220
 221     /* change to calling user's real uid and gid, retaining supplemental
 222      * groups and CAP_NET_ADMIN */
 223     if (capng_change_id(getuid(), getgid(), CAPNG_CLEAR_BOUNDING)) {
 224         return -1;
 225     }
 226
 227     return 0;
 228 }
 229 #endif
 230
 231 int main(int argc, char **argv)
 232 {
 233     struct ifreq ifr;
 234 #ifndef SIOCBRADDIF
 235     unsigned long ifargs[4];
 236 #endif
 237     int ifindex;
 238     int fd = -1, ctlfd = -1, unixfd = -1;
 239     int use_vnet = 0;
 240     int mtu;
 241     const char *bridge = NULL;
 242     char iface[IFNAMSIZ];
 243     int index;
 244     ACLRule *acl_rule;
 245     ACLList acl_list;
 246     int access_allowed, access_denied;
 247     int ret = EXIT_SUCCESS;
 248
 249 #ifdef CONFIG_LIBCAP
 250     /* if we're run from an suid binary, immediately drop privileges preserving
 251      * cap_net_admin */
 252     if (geteuid() == 0 && getuid() != geteuid()) {
 253         if (drop_privileges() == -1) {
 254             fprintf(stderr, "failed to drop privileges\n");
 255             return 1;
 256         }
 257     }
 258 #endif
 259
 260     /* parse arguments */
 261     for (index = 1; index < argc; index++) {
 262         if (strcmp(argv[index], "--use-vnet") == 0) {
 263             use_vnet = 1;
 264         } else if (strncmp(argv[index], "--br=", 5) == 0) {
 265             bridge = &argv[index][5];
 266         } else if (strncmp(argv[index], "--fd=", 5) == 0) {
 267             unixfd = atoi(&argv[index][5]);
 268         } else {
 269             usage();
 270             return EXIT_FAILURE;
 271         }
 272     }
 273
 274     if (bridge == NULL || unixfd == -1) {
 275         usage();
 276         return EXIT_FAILURE;
 277     }
 278     if (strlen(bridge) >= IFNAMSIZ) {
 279         fprintf(stderr, "name `%s' too long: %zu\n", bridge, strlen(bridge));
 280         return EXIT_FAILURE;
 281     }
 282
 283     /* parse default acl file */
 284     QSIMPLEQ_INIT(&acl_list);
 285     if (parse_acl_file(DEFAULT_ACL_FILE, &acl_list) == -1) {
 286         fprintf(stderr, "failed to parse default acl file `%s'\n",
 287                 DEFAULT_ACL_FILE);
 288         ret = EXIT_FAILURE;
 289         goto cleanup;
 290     }
 291
 292     /* validate bridge against acl -- default policy is to deny
 293      * according acl policy if we have a deny and allow both
 294      * then deny should always win over allow
 295      */
 296     access_allowed = 0;
 297     access_denied = 0;
 298     QSIMPLEQ_FOREACH(acl_rule, &acl_list, entry) {
 299         switch (acl_rule->type) {
 300         case ACL_ALLOW_ALL:
 301             access_allowed = 1;
 302             break;
 303         case ACL_ALLOW:
 304             if (strcmp(bridge, acl_rule->iface) == 0) {
 305                 access_allowed = 1;
 306             }
 307             break;
 308         case ACL_DENY_ALL:
 309             access_denied = 1;
 310             break;
 311         case ACL_DENY:
 312             if (strcmp(bridge, acl_rule->iface) == 0) {
 313                 access_denied = 1;
 314             }
 315             break;
 316         }
 317     }
 318
 319     if ((access_allowed == 0) || (access_denied == 1)) {
 320         fprintf(stderr, "access denied by acl file\n");
 321         ret = EXIT_FAILURE;
 322         goto cleanup;
 323     }
 324
 325     /* open a socket to use to control the network interfaces */
 326     ctlfd = socket(AF_INET, SOCK_STREAM, 0);
 327     if (ctlfd == -1) {
 328         fprintf(stderr, "failed to open control socket: %s\n", strerror(errno));
 329         ret = EXIT_FAILURE;
 330         goto cleanup;
 331     }
 332
 333     /* open the tap device */
 334     fd = open("/dev/net/tun", O_RDWR);
 335     if (fd == -1) {
 336         fprintf(stderr, "failed to open /dev/net/tun: %s\n", strerror(errno));
 337         ret = EXIT_FAILURE;
 338         goto cleanup;
 339     }
 340
 341     /* request a tap device, disable PI, and add vnet header support if
 342      * requested and it's available. */
 343     prep_ifreq(&ifr, "tap%d");
 344     ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
 345     if (use_vnet && has_vnet_hdr(fd)) {
 346         ifr.ifr_flags |= IFF_VNET_HDR;
 347     }
 348
 349     if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
 350         fprintf(stderr, "failed to create tun device: %s\n", strerror(errno));
 351         ret = EXIT_FAILURE;
 352         goto cleanup;
 353     }
 354
 355     /* save tap device name */
 356     snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);
 357
 358     /* get the mtu of the bridge */
 359     prep_ifreq(&ifr, bridge);
 360     if (ioctl(ctlfd, SIOCGIFMTU, &ifr) == -1) {
 361         fprintf(stderr, "failed to get mtu of bridge `%s': %s\n",
 362                 bridge, strerror(errno));
 363         ret = EXIT_FAILURE;
 364         goto cleanup;
 365     }
 366
 367     /* save mtu */
 368     mtu = ifr.ifr_mtu;
 369
 370     /* set the mtu of the interface based on the bridge */
 371     prep_ifreq(&ifr, iface);
 372     ifr.ifr_mtu = mtu;
 373     if (ioctl(ctlfd, SIOCSIFMTU, &ifr) == -1) {
 374         fprintf(stderr, "failed to set mtu of device `%s' to %d: %s\n",
 375                 iface, mtu, strerror(errno));
 376         ret = EXIT_FAILURE;
 377         goto cleanup;
 378     }
 379
 380     /* Linux uses the lowest enslaved MAC address as the MAC address of
 381      * the bridge.  Set MAC address to a high value so that it doesn't
 382      * affect the MAC address of the bridge.
 383      */
 384     if (ioctl(ctlfd, SIOCGIFHWADDR, &ifr) < 0) {
 385         fprintf(stderr, "failed to get MAC address of device `%s': %s\n",
 386                 iface, strerror(errno));
 387         ret = EXIT_FAILURE;
 388         goto cleanup;
 389     }
 390     ifr.ifr_hwaddr.sa_data[0] = 0xFE;
 391     if (ioctl(ctlfd, SIOCSIFHWADDR, &ifr) < 0) {
 392         fprintf(stderr, "failed to set MAC address of device `%s': %s\n",
 393                 iface, strerror(errno));
 394         ret = EXIT_FAILURE;
 395         goto cleanup;
 396     }
 397
 398     /* add the interface to the bridge */
 399     prep_ifreq(&ifr, bridge);
 400     ifindex = if_nametoindex(iface);
 401 #ifndef SIOCBRADDIF
 402     ifargs[0] = BRCTL_ADD_IF;
 403     ifargs[1] = ifindex;
 404     ifargs[2] = 0;
 405     ifargs[3] = 0;
 406     ifr.ifr_data = (void *)ifargs;
 407     ret = ioctl(ctlfd, SIOCDEVPRIVATE, &ifr);
 408 #else
 409     ifr.ifr_ifindex = ifindex;
 410     ret = ioctl(ctlfd, SIOCBRADDIF, &ifr);
 411 #endif
 412     if (ret == -1) {
 413         fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
 414                 iface, bridge, strerror(errno));
 415         ret = EXIT_FAILURE;
 416         goto cleanup;
 417     }
 418
 419     /* bring the interface up */
 420     prep_ifreq(&ifr, iface);
 421     if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
 422         fprintf(stderr, "failed to get interface flags for `%s': %s\n",
 423                 iface, strerror(errno));
 424         ret = EXIT_FAILURE;
 425         goto cleanup;
 426     }
 427
 428     ifr.ifr_flags |= IFF_UP;
 429     if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
 430         fprintf(stderr, "failed to bring up interface `%s': %s\n",
 431                 iface, strerror(errno));
 432         ret = EXIT_FAILURE;
 433         goto cleanup;
 434     }
 435
 436     /* write fd to the domain socket */
 437     if (send_fd(unixfd, fd) == -1) {
 438         fprintf(stderr, "failed to write fd to unix socket: %s\n",
 439                 strerror(errno));
 440         ret = EXIT_FAILURE;
 441         goto cleanup;
 442     }
 443
 444     /* ... */
 445
 446     /* profit! */
 447
 448 cleanup:
 449     if (fd >= 0) {
 450         close(fd);
 451     }
 452     if (ctlfd >= 0) {
 453         close(ctlfd);
 454     }
 455     while ((acl_rule = QSIMPLEQ_FIRST(&acl_list)) != NULL) {
 456         QSIMPLEQ_REMOVE_HEAD(&acl_list, entry);
 457         g_free(acl_rule);
 458     }
 459
 460     return ret;
 461 }