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 (g_ascii_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 (g_ascii_isspace(*arg)) { 103 arg++; 104 } 105 106 argend = arg + strlen(arg); 107 while (arg != argend && g_ascii_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 } 442