src/odhcpd.c

   1 /**
   2  * Copyright (C) 2012-2013 Steven Barth <steven@midlink.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License v2 as published by
   6  * the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  *
  13  */
  14
  15 #include <time.h>
  16 #include <errno.h>
  17 #include <fcntl.h>
  18 #include <stdio.h>
  19 #include <resolv.h>
  20 #include <getopt.h>
  21 #include <stddef.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <unistd.h>
  25 #include <signal.h>
  26 #include <stdbool.h>
  27
  28 #include <arpa/inet.h>
  29 #include <net/if.h>
  30 #include <netinet/ip6.h>
  31 #include <netpacket/packet.h>
  32 #include <linux/rtnetlink.h>
  33
  34 #include <sys/socket.h>
  35 #include <sys/ioctl.h>
  36 #include <sys/epoll.h>
  37 #include <sys/types.h>
  38 #include <sys/wait.h>
  39 #include <sys/syscall.h>
  40
  41 #include <libubox/uloop.h>
  42 #include "odhcpd.h"
  43
  44
  45
  46 static int ioctl_sock;
  47 static int rtnl_socket = -1;
  48 static int rtnl_seq = 0;
  49 static int urandom_fd = -1;
  50
  51
  52 static void sighandler(_unused int signal)
  53 {
  54         uloop_end();
  55 }
  56
  57
  58 int main()
  59 {
  60         openlog("odhcpd", LOG_PERROR | LOG_PID, LOG_DAEMON);
  61         setlogmask(LOG_UPTO(LOG_WARNING));
  62         uloop_init();
  63
  64         if (getuid() != 0) {
  65                 syslog(LOG_ERR, "Must be run as root!");
  66                 return 2;
  67         }
  68
  69         ioctl_sock = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);
  70
  71         if ((rtnl_socket = odhcpd_open_rtnl()) < 0) {
  72                 syslog(LOG_ERR, "Unable to open socket: %s", strerror(errno));
  73                 return 2;
  74         }
  75
  76         if ((urandom_fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC)) < 0)
  77                 return 4;
  78
  79         signal(SIGUSR1, SIG_IGN);
  80         signal(SIGINT, sighandler);
  81         signal(SIGTERM, sighandler);
  82
  83         if (init_router())
  84                 return 4;
  85
  86         if (init_dhcpv6())
  87                 return 4;
  88
  89         if (init_ndp())
  90                 return 4;
  91
  92         if (init_dhcpv4())
  93                 return 4;
  94
  95         odhcpd_run();
  96         return 0;
  97 }
  98
  99 int odhcpd_open_rtnl(void)
 100 {
 101         int sock = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
 102
 103         // Connect to the kernel netlink interface
 104         struct sockaddr_nl nl = {.nl_family = AF_NETLINK};
 105         if (connect(sock, (struct sockaddr*)&nl, sizeof(nl))) {
 106                 syslog(LOG_ERR, "Failed to connect to kernel rtnetlink: %s",
 107                                 strerror(errno));
 108                 return -1;
 109         }
 110
 111         return sock;
 112 }
 113
 114
 115 // Read IPv6 MTU for interface
 116 int odhcpd_get_interface_config(const char *ifname, const char *what)
 117 {
 118         char buf[64];
 119         const char *sysctl_pattern = "/proc/sys/net/ipv6/conf/%s/%s";
 120         snprintf(buf, sizeof(buf), sysctl_pattern, ifname, what);
 121
 122         int fd = open(buf, O_RDONLY);
 123         ssize_t len = read(fd, buf, sizeof(buf) - 1);
 124         close(fd);
 125
 126         if (len < 0)
 127                 return -1;
 128
 129         buf[len] = 0;
 130         return atoi(buf);
 131 }
 132
 133
 134 // Read IPv6 MAC for interface
 135 int odhcpd_get_mac(const struct interface *iface, uint8_t mac[6])
 136 {
 137         struct ifreq ifr;
 138         memset(&ifr, 0, sizeof(ifr));
 139         strncpy(ifr.ifr_name, iface->ifname, sizeof(ifr.ifr_name));
 140         if (ioctl(ioctl_sock, SIOCGIFHWADDR, &ifr) < 0)
 141                 return -1;
 142         memcpy(mac, ifr.ifr_hwaddr.sa_data, 6);
 143         return 0;
 144 }
 145
 146
 147 // Forwards a packet on a specific interface
 148 ssize_t odhcpd_send(int socket, struct sockaddr_in6 *dest,
 149                 struct iovec *iov, size_t iov_len,
 150                 const struct interface *iface)
 151 {
 152         // Construct headers
 153         uint8_t cmsg_buf[CMSG_SPACE(sizeof(struct in6_pktinfo))] = {0};
 154         struct msghdr msg = {
 155                 .msg_name = (void *) dest,
 156                 .msg_namelen = sizeof(*dest),
 157                 .msg_iov = iov,
 158                 .msg_iovlen = iov_len,
 159                 .msg_control = cmsg_buf,
 160                 .msg_controllen = sizeof(cmsg_buf),
 161                 .msg_flags = 0
 162         };
 163
 164         // Set control data (define destination interface)
 165         struct cmsghdr *chdr = CMSG_FIRSTHDR(&msg);
 166         chdr->cmsg_level = IPPROTO_IPV6;
 167         chdr->cmsg_type = IPV6_PKTINFO;
 168         chdr->cmsg_len = CMSG_LEN(sizeof(struct in6_pktinfo));
 169         struct in6_pktinfo *pktinfo = (struct in6_pktinfo*)CMSG_DATA(chdr);
 170         pktinfo->ipi6_ifindex = iface->ifindex;
 171
 172         // Also set scope ID if link-local
 173         if (IN6_IS_ADDR_LINKLOCAL(&dest->sin6_addr)
 174                         || IN6_IS_ADDR_MC_LINKLOCAL(&dest->sin6_addr))
 175                 dest->sin6_scope_id = iface->ifindex;
 176
 177         char ipbuf[INET6_ADDRSTRLEN];
 178         inet_ntop(AF_INET6, &dest->sin6_addr, ipbuf, sizeof(ipbuf));
 179
 180         ssize_t sent = sendmsg(socket, &msg, MSG_DONTWAIT);
 181         if (sent < 0)
 182                 syslog(LOG_NOTICE, "Failed to send to %s%%%s (%s)",
 183                                 ipbuf, iface->ifname, strerror(errno));
 184         else
 185                 syslog(LOG_DEBUG, "Sent %li bytes to %s%%%s",
 186                                 (long)sent, ipbuf, iface->ifname);
 187         return sent;
 188 }
 189
 190
 191 int odhcpd_iterate_interface_neighbors(const struct interface *iface,
 192                 void(*cb_neigh)(const struct in6_addr *addr,
 193                                 const struct interface *iface, void *data), void *data)
 194 {
 195         struct {
 196                 struct nlmsghdr nhm;
 197                 struct ndmsg ndm;
 198         } req = {{sizeof(req), RTM_GETNEIGH, NLM_F_REQUEST | NLM_F_DUMP,
 199                         ++rtnl_seq, 0}, {AF_INET6, 0, 0, iface->ifindex, 0, 0, 0}};
 200
 201         if (send(rtnl_socket, &req, sizeof(req), 0) < (ssize_t)sizeof(req))
 202                 return -1;
 203
 204         uint8_t buf[8192];
 205         ssize_t len = 0;
 206
 207         for (struct nlmsghdr *nhm = NULL; ; nhm = NLMSG_NEXT(nhm, len)) {
 208                 while (len < 0 || !NLMSG_OK(nhm, (size_t)len)) {
 209                         len = recv(rtnl_socket, buf, sizeof(buf), 0);
 210                         nhm = (struct nlmsghdr*)buf;
 211                         if (len < 0 || !NLMSG_OK(nhm, (size_t)len)) {
 212                                 if (errno == EINTR)
 213                                         continue;
 214                                 else
 215                                         return -1;
 216                         }
 217                 }
 218
 219                 if (nhm->nlmsg_type != RTM_NEWNEIGH)
 220                         break;
 221
 222                 struct ndmsg *ndm = NLMSG_DATA(nhm);
 223                 if (ndm->ndm_ifindex != iface->ifindex ||
 224                                 !(ndm->ndm_state & (NUD_STALE | NUD_REACHABLE | NUD_PERMANENT)))
 225                         continue;
 226
 227                 struct rtattr *rta = (struct rtattr*)&ndm[1];
 228                 size_t alen = NLMSG_PAYLOAD(nhm, sizeof(*ndm));
 229
 230                 while (RTA_OK(rta, alen)) {
 231                         if (rta->rta_type == NDA_DST &&
 232                                         RTA_PAYLOAD(rta) == sizeof(struct in6_addr)) {
 233                                 cb_neigh(RTA_DATA(rta), iface, data);
 234                                 break;
 235                         } else {
 236                                 rta = RTA_NEXT(rta, alen);
 237                         }
 238                 }
 239
 240         }
 241
 242         return 0;
 243 }
 244
 245
 246 // Detect an IPV6-address currently assigned to the given interface
 247 ssize_t odhcpd_get_interface_addresses(int ifindex,
 248                 struct odhcpd_ipaddr *addrs, size_t cnt)
 249 {
 250         struct {
 251                 struct nlmsghdr nhm;
 252                 struct ifaddrmsg ifa;
 253         } req = {{sizeof(req), RTM_GETADDR, NLM_F_REQUEST | NLM_F_DUMP,
 254                         ++rtnl_seq, 0}, {AF_INET6, 0, 0, 0, ifindex}};
 255         if (send(rtnl_socket, &req, sizeof(req), 0) < (ssize_t)sizeof(req))
 256                 return 0;
 257
 258         uint8_t buf[8192];
 259         ssize_t len = 0, ret = 0;
 260
 261         for (struct nlmsghdr *nhm = NULL; ; nhm = NLMSG_NEXT(nhm, len)) {
 262                 while (len < 0 || !NLMSG_OK(nhm, (size_t)len)) {
 263                         len = recv(rtnl_socket, buf, sizeof(buf), 0);
 264                         nhm = (struct nlmsghdr*)buf;
 265                         if (len < 0 || !NLMSG_OK(nhm, (size_t)len)) {
 266                                 if (errno == EINTR)
 267                                         continue;
 268                                 else
 269                                         return ret;
 270                         }
 271                 }
 272
 273                 if (nhm->nlmsg_type != RTM_NEWADDR)
 274                         break;
 275
 276                 // Skip address but keep clearing socket buffer
 277                 if (ret >= (ssize_t)cnt)
 278                         continue;
 279
 280                 struct ifaddrmsg *ifa = NLMSG_DATA(nhm);
 281                 if (ifa->ifa_scope != RT_SCOPE_UNIVERSE ||
 282                                 (ifindex && ifa->ifa_index != (unsigned)ifindex))
 283                         continue;
 284
 285                 struct rtattr *rta = (struct rtattr*)&ifa[1];
 286                 size_t alen = NLMSG_PAYLOAD(nhm, sizeof(*ifa));
 287                 memset(&addrs[ret], 0, sizeof(addrs[ret]));
 288                 addrs[ret].prefix = ifa->ifa_prefixlen;
 289
 290                 while (RTA_OK(rta, alen)) {
 291                         if (rta->rta_type == IFA_ADDRESS) {
 292                                 memcpy(&addrs[ret].addr, RTA_DATA(rta),
 293                                                 sizeof(struct in6_addr));
 294                         } else if (rta->rta_type == IFA_CACHEINFO) {
 295                                 struct ifa_cacheinfo *ifc = RTA_DATA(rta);
 296                                 addrs[ret].preferred = ifc->ifa_prefered;
 297                                 addrs[ret].valid = ifc->ifa_valid;
 298                         }
 299
 300                         rta = RTA_NEXT(rta, alen);
 301                 }
 302
 303                 if (ifa->ifa_flags & IFA_F_DEPRECATED)
 304                         addrs[ret].preferred = 0;
 305
 306                 ++ret;
 307         }
 308
 309         return ret;
 310 }
 311
 312 int odhcpd_get_preferred_interface_address(int ifindex, struct in6_addr *addr)
 313 {
 314         struct odhcpd_ipaddr ipaddrs[8];
 315         ssize_t ip_cnt = odhcpd_get_interface_addresses(ifindex, ipaddrs, ARRAY_SIZE(ipaddrs));
 316         uint32_t preferred = 0;
 317         int ret = 0;
 318
 319         for (ssize_t i = 0; i < ip_cnt; i++) {
 320                 struct odhcpd_ipaddr *ipaddr = &ipaddrs[i];
 321
 322                 if (ipaddr->preferred > preferred || !preferred) {
 323                         preferred = ipaddr->preferred;
 324                         *addr = ipaddr->addr;
 325                         ret = 1;
 326                 }
 327         }
 328
 329         return ret;
 330 }
 331
 332 void odhcpd_setup_route(const struct in6_addr *addr, int prefixlen,
 333                 const struct interface *iface, const struct in6_addr *gw,
 334                 int metric, bool add)
 335 {
 336         struct req {
 337                 struct nlmsghdr nh;
 338                 struct rtmsg rtm;
 339                 struct rtattr rta_dst;
 340                 struct in6_addr dst_addr;
 341                 struct rtattr rta_oif;
 342                 uint32_t ifindex;
 343                 struct rtattr rta_table;
 344                 uint32_t table;
 345                 struct rtattr rta_prio;
 346                 uint32_t prio;
 347                 struct rtattr rta_gw;
 348                 struct in6_addr gw;
 349         } req = {
 350                 {sizeof(req), 0, NLM_F_REQUEST, ++rtnl_seq, 0},
 351                 {AF_INET6, prefixlen, 0, 0, 0, 0, 0, 0, 0},
 352                 {sizeof(struct rtattr) + sizeof(struct in6_addr), RTA_DST},
 353                 *addr,
 354                 {sizeof(struct rtattr) + sizeof(uint32_t), RTA_OIF},
 355                 iface->ifindex,
 356                 {sizeof(struct rtattr) + sizeof(uint32_t), RTA_TABLE},
 357                 RT_TABLE_MAIN,
 358                 {sizeof(struct rtattr) + sizeof(uint32_t), RTA_PRIORITY},
 359                 metric,
 360                 {sizeof(struct rtattr) + sizeof(struct in6_addr), RTA_GATEWAY},
 361                 IN6ADDR_ANY_INIT,
 362         };
 363
 364         if (gw)
 365                 req.gw = *gw;
 366
 367         if (add) {
 368                 req.nh.nlmsg_type = RTM_NEWROUTE;
 369                 req.nh.nlmsg_flags |= (NLM_F_CREATE | NLM_F_REPLACE);
 370                 req.rtm.rtm_protocol = RTPROT_STATIC;
 371                 req.rtm.rtm_scope = (gw) ? RT_SCOPE_UNIVERSE : RT_SCOPE_LINK;
 372                 req.rtm.rtm_type = RTN_UNICAST;
 373         } else {
 374                 req.nh.nlmsg_type = RTM_DELROUTE;
 375                 req.rtm.rtm_scope = RT_SCOPE_NOWHERE;
 376         }
 377
 378         req.nh.nlmsg_len = (gw) ? sizeof(req) : offsetof(struct req, rta_gw);
 379         send(rtnl_socket, &req, req.nh.nlmsg_len, MSG_DONTWAIT);
 380 }
 381
 382 struct interface* odhcpd_get_interface_by_index(int ifindex)
 383 {
 384         struct interface *iface;
 385         list_for_each_entry(iface, &interfaces, head)
 386                 if (iface->ifindex == ifindex)
 387                         return iface;
 388
 389         return NULL;
 390 }
 391
 392
 393 struct interface* odhcpd_get_interface_by_name(const char *name)
 394 {
 395         struct interface *iface;
 396         list_for_each_entry(iface, &interfaces, head)
 397                 if (!strcmp(iface->ifname, name))
 398                         return iface;
 399
 400         return NULL;
 401 }
 402
 403
 404 struct interface* odhcpd_get_master_interface(void)
 405 {
 406         struct interface *iface;
 407         list_for_each_entry(iface, &interfaces, head)
 408                 if (iface->master)
 409                         return iface;
 410
 411         return NULL;
 412 }
 413
 414
 415 // Convenience function to receive and do basic validation of packets
 416 static void odhcpd_receive_packets(struct uloop_fd *u, _unused unsigned int events)
 417 {
 418         struct odhcpd_event *e = container_of(u, struct odhcpd_event, uloop);
 419
 420         uint8_t data_buf[RELAYD_BUFFER_SIZE], cmsg_buf[128];
 421         union {
 422                 struct sockaddr_in6 in6;
 423                 struct sockaddr_in in;
 424                 struct sockaddr_ll ll;
 425                 struct sockaddr_nl nl;
 426         } addr;
 427
 428         while (true) {
 429                 struct iovec iov = {data_buf, sizeof(data_buf)};
 430                 struct msghdr msg = {
 431                         .msg_name = (void *) &addr,
 432                         .msg_namelen = sizeof(addr),
 433                         .msg_iov = &iov,
 434                         .msg_iovlen = 1,
 435                         .msg_control = cmsg_buf,
 436                         .msg_controllen = sizeof(cmsg_buf),
 437                         .msg_flags = 0
 438                 };
 439
 440                 ssize_t len = recvmsg(u->fd, &msg, MSG_DONTWAIT);
 441                 if (len < 0) {
 442                         if (errno == EAGAIN)
 443                                 break;
 444                         else
 445                                 continue;
 446                 }
 447
 448
 449                 // Extract destination interface
 450                 int destiface = 0;
 451                 int *hlim = NULL;
 452                 void *dest = NULL;
 453                 struct in6_pktinfo *pktinfo;
 454                 struct in_pktinfo *pkt4info;
 455                 for (struct cmsghdr *ch = CMSG_FIRSTHDR(&msg); ch != NULL; ch = CMSG_NXTHDR(&msg, ch)) {
 456                         if (ch->cmsg_level == IPPROTO_IPV6 &&
 457                                         ch->cmsg_type == IPV6_PKTINFO) {
 458                                 pktinfo = (struct in6_pktinfo*)CMSG_DATA(ch);
 459                                 destiface = pktinfo->ipi6_ifindex;
 460                                 dest = &pktinfo->ipi6_addr;
 461                         } else if (ch->cmsg_level == IPPROTO_IP &&
 462                                         ch->cmsg_type == IP_PKTINFO) {
 463                                 pkt4info = (struct in_pktinfo*)CMSG_DATA(ch);
 464                                 destiface = pkt4info->ipi_ifindex;
 465                                 dest = &pkt4info->ipi_addr;
 466                         } else if (ch->cmsg_level == IPPROTO_IPV6 &&
 467                                         ch->cmsg_type == IPV6_HOPLIMIT) {
 468                                 hlim = (int*)CMSG_DATA(ch);
 469                         }
 470                 }
 471
 472                 // Check hoplimit if received
 473                 if (hlim && *hlim != 255)
 474                         continue;
 475
 476                 // Detect interface for packet sockets
 477                 if (addr.ll.sll_family == AF_PACKET)
 478                         destiface = addr.ll.sll_ifindex;
 479
 480                 struct interface *iface =
 481                                 odhcpd_get_interface_by_index(destiface);
 482
 483                 if (!iface && addr.nl.nl_family != AF_NETLINK)
 484                         continue;
 485
 486                 char ipbuf[INET6_ADDRSTRLEN] = "kernel";
 487                 if (addr.ll.sll_family == AF_PACKET &&
 488                                 len >= (ssize_t)sizeof(struct ip6_hdr))
 489                         inet_ntop(AF_INET6, &data_buf[8], ipbuf, sizeof(ipbuf));
 490                 else if (addr.in6.sin6_family == AF_INET6)
 491                         inet_ntop(AF_INET6, &addr.in6.sin6_addr, ipbuf, sizeof(ipbuf));
 492                 else if (addr.in.sin_family == AF_INET)
 493                         inet_ntop(AF_INET, &addr.in.sin_addr, ipbuf, sizeof(ipbuf));
 494
 495                 syslog(LOG_DEBUG, "--");
 496                 syslog(LOG_DEBUG, "Received %li Bytes from %s%%%s", (long)len,
 497                                 ipbuf, (iface) ? iface->ifname : "netlink");
 498
 499                 e->handle_dgram(&addr, data_buf, len, iface, dest);
 500         }
 501 }
 502
 503 // Register events for the multiplexer
 504 int odhcpd_register(struct odhcpd_event *event)
 505 {
 506         event->uloop.cb = odhcpd_receive_packets;
 507         return uloop_fd_add(&event->uloop, ULOOP_READ);
 508 }
 509
 510 void odhcpd_process(struct odhcpd_event *event)
 511 {
 512         odhcpd_receive_packets(&event->uloop, 0);
 513 }
 514
 515 int odhcpd_urandom(void *data, size_t len)
 516 {
 517         return read(urandom_fd, data, len);
 518 }
 519
 520
 521 time_t odhcpd_time(void)
 522 {
 523         struct timespec ts;
 524         syscall(SYS_clock_gettime, CLOCK_MONOTONIC, &ts);
 525         return ts.tv_sec;
 526 }
 527
 528
 529 static const char hexdigits[] = "0123456789abcdef";
 530 static const int8_t hexvals[] = {
 531     -1, -1, -1, -1, -1, -1, -1, -1, -1, -2, -2, -1, -1, -2, -1, -1,
 532     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 533     -2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 534      0,  1,  2,  3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1,
 535     -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 536     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 537     -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 538     -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 539 };
 540
 541 ssize_t odhcpd_unhexlify(uint8_t *dst, size_t len, const char *src)
 542 {
 543         size_t c;
 544         for (c = 0; c < len && src[0] && src[1]; ++c) {
 545                 int8_t x = (int8_t)*src++;
 546                 int8_t y = (int8_t)*src++;
 547                 if (x < 0 || (x = hexvals[x]) < 0
 548                                 || y < 0 || (y = hexvals[y]) < 0)
 549                         return -1;
 550                 dst[c] = x << 4 | y;
 551                 while (((int8_t)*src) < 0 ||
 552                                 (*src && hexvals[(uint8_t)*src] < 0))
 553                         src++;
 554         }
 555
 556         return c;
 557 }
 558
 559
 560 void odhcpd_hexlify(char *dst, const uint8_t *src, size_t len)
 561 {
 562         for (size_t i = 0; i < len; ++i) {
 563                 *dst++ = hexdigits[src[i] >> 4];
 564                 *dst++ = hexdigits[src[i] & 0x0f];
 565         }
 566         *dst = 0;
 567 }
 568
 569
 570 int odhcpd_bmemcmp(const void *av, const void *bv, size_t bits)
 571 {
 572         const uint8_t *a = av, *b = bv;
 573         size_t bytes = bits / 8;
 574         bits %= 8;
 575
 576         int res = memcmp(a, b, bytes);
 577         if (res == 0 && bits > 0)
 578                 res = (a[bytes] >> (8 - bits)) - (b[bytes] >> (8 - bits));
 579
 580         return res;
 581 }
 582
 583
 584 void odhcpd_bmemcpy(void *av, const void *bv, size_t bits)
 585 {
 586         uint8_t *a = av;
 587         const uint8_t *b = bv;
 588
 589         size_t bytes = bits / 8;
 590         bits %= 8;
 591         memcpy(a, b, bytes);
 592
 593         if (bits > 0) {
 594                 uint8_t mask = (1 << (8 - bits)) - 1;
 595                 a[bytes] = (a[bytes] & mask) | ((~mask) & b[bytes]);
 596         }
 597 }