src/libudev/libudev-monitor.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2008-2012 Kay Sievers <kay@vrfy.org>
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <linux/filter.h>
  22 #include <linux/netlink.h>
  23 #include <poll.h>
  24 #include <stddef.h>
  25 #include <stdio.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28 #include <sys/socket.h>
  29 #include <unistd.h>
  30
  31 #include "libudev.h"
  32
  33 #include "alloc-util.h"
  34 #include "fd-util.h"
  35 #include "fileio.h"
  36 #include "formats-util.h"
  37 #include "libudev-private.h"
  38 #include "missing.h"
  39 #include "mount-util.h"
  40 #include "socket-util.h"
  41 #include "string-util.h"
  42
  43 /**
  44  * SECTION:libudev-monitor
  45  * @short_description: device event source
  46  *
  47  * Connects to a device event source.
  48  */
  49
  50 /**
  51  * udev_monitor:
  52  *
  53  * Opaque object handling an event source.
  54  */
  55 struct udev_monitor {
  56         struct udev *udev;
  57         int refcount;
  58         int sock;
  59         union sockaddr_union snl;
  60         union sockaddr_union snl_trusted_sender;
  61         union sockaddr_union snl_destination;
  62         socklen_t addrlen;
  63         struct udev_list filter_subsystem_list;
  64         struct udev_list filter_tag_list;
  65         bool bound;
  66 };
  67
  68 enum udev_monitor_netlink_group {
  69         UDEV_MONITOR_NONE,
  70         UDEV_MONITOR_KERNEL,
  71         UDEV_MONITOR_UDEV,
  72 };
  73
  74 #define UDEV_MONITOR_MAGIC                0xfeedcafe
  75 struct udev_monitor_netlink_header {
  76         /* "libudev" prefix to distinguish libudev and kernel messages */
  77         char prefix[8];
  78         /*
  79          * magic to protect against daemon <-> library message format mismatch
  80          * used in the kernel from socket filter rules; needs to be stored in network order
  81          */
  82         unsigned int magic;
  83         /* total length of header structure known to the sender */
  84         unsigned int header_size;
  85         /* properties string buffer */
  86         unsigned int properties_off;
  87         unsigned int properties_len;
  88         /*
  89          * hashes of primary device properties strings, to let libudev subscribers
  90          * use in-kernel socket filters; values need to be stored in network order
  91          */
  92         unsigned int filter_subsystem_hash;
  93         unsigned int filter_devtype_hash;
  94         unsigned int filter_tag_bloom_hi;
  95         unsigned int filter_tag_bloom_lo;
  96 };
  97
  98 static struct udev_monitor *udev_monitor_new(struct udev *udev)
  99 {
 100         struct udev_monitor *udev_monitor;
 101
 102         udev_monitor = new0(struct udev_monitor, 1);
 103         if (udev_monitor == NULL)
 104                 return NULL;
 105         udev_monitor->refcount = 1;
 106         udev_monitor->udev = udev;
 107         udev_list_init(udev, &udev_monitor->filter_subsystem_list, false);
 108         udev_list_init(udev, &udev_monitor->filter_tag_list, true);
 109         return udev_monitor;
 110 }
 111
 112 /* we consider udev running when /dev is on devtmpfs */
 113 static bool udev_has_devtmpfs(struct udev *udev) {
 114
 115         union file_handle_union h = FILE_HANDLE_INIT;
 116         _cleanup_fclose_ FILE *f = NULL;
 117         char line[LINE_MAX], *e;
 118         int mount_id;
 119         int r;
 120
 121         r = name_to_handle_at(AT_FDCWD, "/dev", &h.handle, &mount_id, 0);
 122         if (r < 0) {
 123                 if (errno != EOPNOTSUPP)
 124                         log_debug_errno(errno, "name_to_handle_at on /dev: %m");
 125                 return false;
 126         }
 127
 128         f = fopen("/proc/self/mountinfo", "re");
 129         if (!f)
 130                 return false;
 131
 132         FOREACH_LINE(line, f, return false) {
 133                 int mid;
 134
 135                 if (sscanf(line, "%i", &mid) != 1)
 136                         continue;
 137
 138                 if (mid != mount_id)
 139                         continue;
 140
 141                 e = strstr(line, " - ");
 142                 if (!e)
 143                         continue;
 144
 145                 /* accept any name that starts with the currently expected type */
 146                 if (startswith(e + 3, "devtmpfs"))
 147                         return true;
 148         }
 149
 150         return false;
 151 }
 152
 153 static void monitor_set_nl_address(struct udev_monitor *udev_monitor) {
 154         union sockaddr_union snl;
 155         socklen_t addrlen;
 156         int r;
 157
 158         assert(udev_monitor);
 159
 160         /* get the address the kernel has assigned us
 161          * it is usually, but not necessarily the pid
 162          */
 163         addrlen = sizeof(struct sockaddr_nl);
 164         r = getsockname(udev_monitor->sock, &snl.sa, &addrlen);
 165         if (r >= 0)
 166                 udev_monitor->snl.nl.nl_pid = snl.nl.nl_pid;
 167 }
 168
 169 struct udev_monitor *udev_monitor_new_from_netlink_fd(struct udev *udev, const char *name, int fd)
 170 {
 171         struct udev_monitor *udev_monitor;
 172         unsigned int group;
 173
 174         if (udev == NULL)
 175                 return NULL;
 176
 177         if (name == NULL)
 178                 group = UDEV_MONITOR_NONE;
 179         else if (streq(name, "udev")) {
 180                 /*
 181                  * We do not support subscribing to uevents if no instance of
 182                  * udev is running. Uevents would otherwise broadcast the
 183                  * processing data of the host into containers, which is not
 184                  * desired.
 185                  *
 186                  * Containers will currently not get any udev uevents, until
 187                  * a supporting infrastructure is available.
 188                  *
 189                  * We do not set a netlink multicast group here, so the socket
 190                  * will not receive any messages.
 191                  */
 192                 if (access("/run/udev/control", F_OK) < 0 && !udev_has_devtmpfs(udev)) {
 193                         log_debug("the udev service seems not to be active, disable the monitor");
 194                         group = UDEV_MONITOR_NONE;
 195                 } else
 196                         group = UDEV_MONITOR_UDEV;
 197         } else if (streq(name, "kernel"))
 198                 group = UDEV_MONITOR_KERNEL;
 199         else
 200                 return NULL;
 201
 202         udev_monitor = udev_monitor_new(udev);
 203         if (udev_monitor == NULL)
 204                 return NULL;
 205
 206         if (fd < 0) {
 207                 udev_monitor->sock = socket(PF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_KOBJECT_UEVENT);
 208                 if (udev_monitor->sock < 0) {
 209                         log_debug_errno(errno, "error getting socket: %m");
 210                         return mfree(udev_monitor);
 211                 }
 212         } else {
 213                 udev_monitor->bound = true;
 214                 udev_monitor->sock = fd;
 215                 monitor_set_nl_address(udev_monitor);
 216         }
 217
 218         udev_monitor->snl.nl.nl_family = AF_NETLINK;
 219         udev_monitor->snl.nl.nl_groups = group;
 220
 221         /* default destination for sending */
 222         udev_monitor->snl_destination.nl.nl_family = AF_NETLINK;
 223         udev_monitor->snl_destination.nl.nl_groups = UDEV_MONITOR_UDEV;
 224
 225         return udev_monitor;
 226 }
 227
 228 /**
 229  * udev_monitor_new_from_netlink:
 230  * @udev: udev library context
 231  * @name: name of event source
 232  *
 233  * Create new udev monitor and connect to a specified event
 234  * source. Valid sources identifiers are "udev" and "kernel".
 235  *
 236  * Applications should usually not connect directly to the
 237  * "kernel" events, because the devices might not be useable
 238  * at that time, before udev has configured them, and created
 239  * device nodes. Accessing devices at the same time as udev,
 240  * might result in unpredictable behavior. The "udev" events
 241  * are sent out after udev has finished its event processing,
 242  * all rules have been processed, and needed device nodes are
 243  * created.
 244  *
 245  * The initial refcount is 1, and needs to be decremented to
 246  * release the resources of the udev monitor.
 247  *
 248  * Returns: a new udev monitor, or #NULL, in case of an error
 249  **/
 250 _public_ struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev, const char *name)
 251 {
 252         return udev_monitor_new_from_netlink_fd(udev, name, -1);
 253 }
 254
 255 static inline void bpf_stmt(struct sock_filter *inss, unsigned int *i,
 256                             unsigned short code, unsigned int data)
 257 {
 258         struct sock_filter *ins = &inss[*i];
 259
 260         ins->code = code;
 261         ins->k = data;
 262         (*i)++;
 263 }
 264
 265 static inline void bpf_jmp(struct sock_filter *inss, unsigned int *i,
 266                            unsigned short code, unsigned int data,
 267                            unsigned short jt, unsigned short jf)
 268 {
 269         struct sock_filter *ins = &inss[*i];
 270
 271         ins->code = code;
 272         ins->jt = jt;
 273         ins->jf = jf;
 274         ins->k = data;
 275         (*i)++;
 276 }
 277
 278 /**
 279  * udev_monitor_filter_update:
 280  * @udev_monitor: monitor
 281  *
 282  * Update the installed socket filter. This is only needed,
 283  * if the filter was removed or changed.
 284  *
 285  * Returns: 0 on success, otherwise a negative error value.
 286  */
 287 _public_ int udev_monitor_filter_update(struct udev_monitor *udev_monitor)
 288 {
 289         struct sock_filter ins[512];
 290         struct sock_fprog filter;
 291         unsigned int i;
 292         struct udev_list_entry *list_entry;
 293         int err;
 294
 295         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL &&
 296             udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
 297                 return 0;
 298
 299         memzero(ins, sizeof(ins));
 300         i = 0;
 301
 302         /* load magic in A */
 303         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, magic));
 304         /* jump if magic matches */
 305         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, UDEV_MONITOR_MAGIC, 1, 0);
 306         /* wrong magic, pass packet */
 307         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 308
 309         if (udev_list_get_entry(&udev_monitor->filter_tag_list) != NULL) {
 310                 int tag_matches;
 311
 312                 /* count tag matches, to calculate end of tag match block */
 313                 tag_matches = 0;
 314                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list))
 315                         tag_matches++;
 316
 317                 /* add all tags matches */
 318                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
 319                         uint64_t tag_bloom_bits = util_string_bloom64(udev_list_entry_get_name(list_entry));
 320                         uint32_t tag_bloom_hi = tag_bloom_bits >> 32;
 321                         uint32_t tag_bloom_lo = tag_bloom_bits & 0xffffffff;
 322
 323                         /* load device bloom bits in A */
 324                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_hi));
 325                         /* clear bits (tag bits & bloom bits) */
 326                         bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_hi);
 327                         /* jump to next tag if it does not match */
 328                         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_hi, 0, 3);
 329
 330                         /* load device bloom bits in A */
 331                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_lo));
 332                         /* clear bits (tag bits & bloom bits) */
 333                         bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_lo);
 334                         /* jump behind end of tag match block if tag matches */
 335                         tag_matches--;
 336                         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_lo, 1 + (tag_matches * 6), 0);
 337                 }
 338
 339                 /* nothing matched, drop packet */
 340                 bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
 341         }
 342
 343         /* add all subsystem matches */
 344         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) != NULL) {
 345                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
 346                         unsigned int hash = util_string_hash32(udev_list_entry_get_name(list_entry));
 347
 348                         /* load device subsystem value in A */
 349                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_subsystem_hash));
 350                         if (udev_list_entry_get_value(list_entry) == NULL) {
 351                                 /* jump if subsystem does not match */
 352                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
 353                         } else {
 354                                 /* jump if subsystem does not match */
 355                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 3);
 356
 357                                 /* load device devtype value in A */
 358                                 bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_devtype_hash));
 359                                 /* jump if value does not match */
 360                                 hash = util_string_hash32(udev_list_entry_get_value(list_entry));
 361                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
 362                         }
 363
 364                         /* matched, pass packet */
 365                         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 366
 367                         if (i+1 >= ELEMENTSOF(ins))
 368                                 return -E2BIG;
 369                 }
 370
 371                 /* nothing matched, drop packet */
 372                 bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
 373         }
 374
 375         /* matched, pass packet */
 376         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 377
 378         /* install filter */
 379         memzero(&filter, sizeof(filter));
 380         filter.len = i;
 381         filter.filter = ins;
 382         err = setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter));
 383         return err < 0 ? -errno : 0;
 384 }
 385
 386 int udev_monitor_allow_unicast_sender(struct udev_monitor *udev_monitor, struct udev_monitor *sender)
 387 {
 388         udev_monitor->snl_trusted_sender.nl.nl_pid = sender->snl.nl.nl_pid;
 389         return 0;
 390 }
 391
 392 /**
 393  * udev_monitor_enable_receiving:
 394  * @udev_monitor: the monitor which should receive events
 395  *
 396  * Binds the @udev_monitor socket to the event source.
 397  *
 398  * Returns: 0 on success, otherwise a negative error value.
 399  */
 400 _public_ int udev_monitor_enable_receiving(struct udev_monitor *udev_monitor)
 401 {
 402         int err = 0;
 403         const int on = 1;
 404
 405         udev_monitor_filter_update(udev_monitor);
 406
 407         if (!udev_monitor->bound) {
 408                 err = bind(udev_monitor->sock,
 409                            &udev_monitor->snl.sa, sizeof(struct sockaddr_nl));
 410                 if (err == 0)
 411                         udev_monitor->bound = true;
 412         }
 413
 414         if (err >= 0)
 415                 monitor_set_nl_address(udev_monitor);
 416         else
 417                 return log_debug_errno(errno, "bind failed: %m");
 418
 419         /* enable receiving of sender credentials */
 420         err = setsockopt(udev_monitor->sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
 421         if (err < 0)
 422                 log_debug_errno(errno, "setting SO_PASSCRED failed: %m");
 423
 424         return 0;
 425 }
 426
 427 /**
 428  * udev_monitor_set_receive_buffer_size:
 429  * @udev_monitor: the monitor which should receive events
 430  * @size: the size in bytes
 431  *
 432  * Set the size of the kernel socket buffer. This call needs the
 433  * appropriate privileges to succeed.
 434  *
 435  * Returns: 0 on success, otherwise -1 on error.
 436  */
 437 _public_ int udev_monitor_set_receive_buffer_size(struct udev_monitor *udev_monitor, int size)
 438 {
 439         if (udev_monitor == NULL)
 440                 return -EINVAL;
 441         return setsockopt(udev_monitor->sock, SOL_SOCKET, SO_RCVBUFFORCE, &size, sizeof(size));
 442 }
 443
 444 int udev_monitor_disconnect(struct udev_monitor *udev_monitor)
 445 {
 446         int err;
 447
 448         err = close(udev_monitor->sock);
 449         udev_monitor->sock = -1;
 450         return err < 0 ? -errno : 0;
 451 }
 452
 453 /**
 454  * udev_monitor_ref:
 455  * @udev_monitor: udev monitor
 456  *
 457  * Take a reference of a udev monitor.
 458  *
 459  * Returns: the passed udev monitor
 460  **/
 461 _public_ struct udev_monitor *udev_monitor_ref(struct udev_monitor *udev_monitor)
 462 {
 463         if (udev_monitor == NULL)
 464                 return NULL;
 465         udev_monitor->refcount++;
 466         return udev_monitor;
 467 }
 468
 469 /**
 470  * udev_monitor_unref:
 471  * @udev_monitor: udev monitor
 472  *
 473  * Drop a reference of a udev monitor. If the refcount reaches zero,
 474  * the bound socket will be closed, and the resources of the monitor
 475  * will be released.
 476  *
 477  * Returns: #NULL
 478  **/
 479 _public_ struct udev_monitor *udev_monitor_unref(struct udev_monitor *udev_monitor)
 480 {
 481         if (udev_monitor == NULL)
 482                 return NULL;
 483         udev_monitor->refcount--;
 484         if (udev_monitor->refcount > 0)
 485                 return NULL;
 486         if (udev_monitor->sock >= 0)
 487                 close(udev_monitor->sock);
 488         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
 489         udev_list_cleanup(&udev_monitor->filter_tag_list);
 490         free(udev_monitor);
 491         return NULL;
 492 }
 493
 494 /**
 495  * udev_monitor_get_udev:
 496  * @udev_monitor: udev monitor
 497  *
 498  * Retrieve the udev library context the monitor was created with.
 499  *
 500  * Returns: the udev library context
 501  **/
 502 _public_ struct udev *udev_monitor_get_udev(struct udev_monitor *udev_monitor)
 503 {
 504         if (udev_monitor == NULL)
 505                 return NULL;
 506         return udev_monitor->udev;
 507 }
 508
 509 /**
 510  * udev_monitor_get_fd:
 511  * @udev_monitor: udev monitor
 512  *
 513  * Retrieve the socket file descriptor associated with the monitor.
 514  *
 515  * Returns: the socket file descriptor
 516  **/
 517 _public_ int udev_monitor_get_fd(struct udev_monitor *udev_monitor)
 518 {
 519         if (udev_monitor == NULL)
 520                 return -EINVAL;
 521         return udev_monitor->sock;
 522 }
 523
 524 static int passes_filter(struct udev_monitor *udev_monitor, struct udev_device *udev_device)
 525 {
 526         struct udev_list_entry *list_entry;
 527
 528         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL)
 529                 goto tag;
 530         udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
 531                 const char *subsys = udev_list_entry_get_name(list_entry);
 532                 const char *dsubsys = udev_device_get_subsystem(udev_device);
 533                 const char *devtype;
 534                 const char *ddevtype;
 535
 536                 if (!streq(dsubsys, subsys))
 537                         continue;
 538
 539                 devtype = udev_list_entry_get_value(list_entry);
 540                 if (devtype == NULL)
 541                         goto tag;
 542                 ddevtype = udev_device_get_devtype(udev_device);
 543                 if (ddevtype == NULL)
 544                         continue;
 545                 if (streq(ddevtype, devtype))
 546                         goto tag;
 547         }
 548         return 0;
 549
 550 tag:
 551         if (udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
 552                 return 1;
 553         udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
 554                 const char *tag = udev_list_entry_get_name(list_entry);
 555
 556                 if (udev_device_has_tag(udev_device, tag))
 557                         return 1;
 558         }
 559         return 0;
 560 }
 561
 562 /**
 563  * udev_monitor_receive_device:
 564  * @udev_monitor: udev monitor
 565  *
 566  * Receive data from the udev monitor socket, allocate a new udev
 567  * device, fill in the received data, and return the device.
 568  *
 569  * Only socket connections with uid=0 are accepted.
 570  *
 571  * The monitor socket is by default set to NONBLOCK. A variant of poll() on
 572  * the file descriptor returned by udev_monitor_get_fd() should to be used to
 573  * wake up when new devices arrive, or alternatively the file descriptor
 574  * switched into blocking mode.
 575  *
 576  * The initial refcount is 1, and needs to be decremented to
 577  * release the resources of the udev device.
 578  *
 579  * Returns: a new udev device, or #NULL, in case of an error
 580  **/
 581 _public_ struct udev_device *udev_monitor_receive_device(struct udev_monitor *udev_monitor)
 582 {
 583         struct udev_device *udev_device;
 584         struct msghdr smsg;
 585         struct iovec iov;
 586         char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
 587         struct cmsghdr *cmsg;
 588         union sockaddr_union snl;
 589         struct ucred *cred;
 590         union {
 591                 struct udev_monitor_netlink_header nlh;
 592                 char raw[8192];
 593         } buf;
 594         ssize_t buflen;
 595         ssize_t bufpos;
 596         bool is_initialized = false;
 597
 598 retry:
 599         if (udev_monitor == NULL)
 600                 return NULL;
 601         iov.iov_base = &buf;
 602         iov.iov_len = sizeof(buf);
 603         memzero(&smsg, sizeof(struct msghdr));
 604         smsg.msg_iov = &iov;
 605         smsg.msg_iovlen = 1;
 606         smsg.msg_control = cred_msg;
 607         smsg.msg_controllen = sizeof(cred_msg);
 608         smsg.msg_name = &snl;
 609         smsg.msg_namelen = sizeof(snl);
 610
 611         buflen = recvmsg(udev_monitor->sock, &smsg, 0);
 612         if (buflen < 0) {
 613                 if (errno != EINTR)
 614                         log_debug("unable to receive message");
 615                 return NULL;
 616         }
 617
 618         if (buflen < 32 || (smsg.msg_flags & MSG_TRUNC)) {
 619                 log_debug("invalid message length");
 620                 return NULL;
 621         }
 622
 623         if (snl.nl.nl_groups == 0) {
 624                 /* unicast message, check if we trust the sender */
 625                 if (udev_monitor->snl_trusted_sender.nl.nl_pid == 0 ||
 626                     snl.nl.nl_pid != udev_monitor->snl_trusted_sender.nl.nl_pid) {
 627                         log_debug("unicast netlink message ignored");
 628                         return NULL;
 629                 }
 630         } else if (snl.nl.nl_groups == UDEV_MONITOR_KERNEL) {
 631                 if (snl.nl.nl_pid > 0) {
 632                         log_debug("multicast kernel netlink message from PID %"PRIu32" ignored",
 633                                   snl.nl.nl_pid);
 634                         return NULL;
 635                 }
 636         }
 637
 638         cmsg = CMSG_FIRSTHDR(&smsg);
 639         if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
 640                 log_debug("no sender credentials received, message ignored");
 641                 return NULL;
 642         }
 643
 644         cred = (struct ucred *)CMSG_DATA(cmsg);
 645         if (cred->uid != 0) {
 646                 log_debug("sender uid="UID_FMT", message ignored", cred->uid);
 647                 return NULL;
 648         }
 649
 650         if (memcmp(buf.raw, "libudev", 8) == 0) {
 651                 /* udev message needs proper version magic */
 652                 if (buf.nlh.magic != htobe32(UDEV_MONITOR_MAGIC)) {
 653                         log_debug("unrecognized message signature (%x != %x)",
 654                                  buf.nlh.magic, htobe32(UDEV_MONITOR_MAGIC));
 655                         return NULL;
 656                 }
 657                 if (buf.nlh.properties_off+32 > (size_t)buflen) {
 658                         log_debug("message smaller than expected (%u > %zd)",
 659                                   buf.nlh.properties_off+32, buflen);
 660                         return NULL;
 661                 }
 662
 663                 bufpos = buf.nlh.properties_off;
 664
 665                 /* devices received from udev are always initialized */
 666                 is_initialized = true;
 667         } else {
 668                 /* kernel message with header */
 669                 bufpos = strlen(buf.raw) + 1;
 670                 if ((size_t)bufpos < sizeof("a@/d") || bufpos >= buflen) {
 671                         log_debug("invalid message length");
 672                         return NULL;
 673                 }
 674
 675                 /* check message header */
 676                 if (strstr(buf.raw, "@/") == NULL) {
 677                         log_debug("unrecognized message header");
 678                         return NULL;
 679                 }
 680         }
 681
 682         udev_device = udev_device_new_from_nulstr(udev_monitor->udev, &buf.raw[bufpos], buflen - bufpos);
 683         if (!udev_device) {
 684                 log_debug("could not create device: %m");
 685                 return NULL;
 686         }
 687
 688         if (is_initialized)
 689                 udev_device_set_is_initialized(udev_device);
 690
 691         /* skip device, if it does not pass the current filter */
 692         if (!passes_filter(udev_monitor, udev_device)) {
 693                 struct pollfd pfd[1];
 694                 int rc;
 695
 696                 udev_device_unref(udev_device);
 697
 698                 /* if something is queued, get next device */
 699                 pfd[0].fd = udev_monitor->sock;
 700                 pfd[0].events = POLLIN;
 701                 rc = poll(pfd, 1, 0);
 702                 if (rc > 0)
 703                         goto retry;
 704                 return NULL;
 705         }
 706
 707         return udev_device;
 708 }
 709
 710 int udev_monitor_send_device(struct udev_monitor *udev_monitor,
 711                              struct udev_monitor *destination, struct udev_device *udev_device)
 712 {
 713         const char *buf, *val;
 714         ssize_t blen, count;
 715         struct udev_monitor_netlink_header nlh = {
 716                 .prefix = "libudev",
 717                 .magic = htobe32(UDEV_MONITOR_MAGIC),
 718                 .header_size = sizeof nlh,
 719         };
 720         struct iovec iov[2] = {
 721                 { .iov_base = &nlh, .iov_len = sizeof nlh },
 722         };
 723         struct msghdr smsg = {
 724                 .msg_iov = iov,
 725                 .msg_iovlen = 2,
 726         };
 727         struct udev_list_entry *list_entry;
 728         uint64_t tag_bloom_bits;
 729
 730         blen = udev_device_get_properties_monitor_buf(udev_device, &buf);
 731         if (blen < 32) {
 732                 log_debug("device buffer is too small to contain a valid device");
 733                 return -EINVAL;
 734         }
 735
 736         /* fill in versioned header */
 737         val = udev_device_get_subsystem(udev_device);
 738         nlh.filter_subsystem_hash = htobe32(util_string_hash32(val));
 739
 740         val = udev_device_get_devtype(udev_device);
 741         if (val != NULL)
 742                 nlh.filter_devtype_hash = htobe32(util_string_hash32(val));
 743
 744         /* add tag bloom filter */
 745         tag_bloom_bits = 0;
 746         udev_list_entry_foreach(list_entry, udev_device_get_tags_list_entry(udev_device))
 747                 tag_bloom_bits |= util_string_bloom64(udev_list_entry_get_name(list_entry));
 748         if (tag_bloom_bits > 0) {
 749                 nlh.filter_tag_bloom_hi = htobe32(tag_bloom_bits >> 32);
 750                 nlh.filter_tag_bloom_lo = htobe32(tag_bloom_bits & 0xffffffff);
 751         }
 752
 753         /* add properties list */
 754         nlh.properties_off = iov[0].iov_len;
 755         nlh.properties_len = blen;
 756         iov[1].iov_base = (char *)buf;
 757         iov[1].iov_len = blen;
 758
 759         /*
 760          * Use custom address for target, or the default one.
 761          *
 762          * If we send to a multicast group, we will get
 763          * ECONNREFUSED, which is expected.
 764          */
 765         if (destination)
 766                 smsg.msg_name = &destination->snl;
 767         else
 768                 smsg.msg_name = &udev_monitor->snl_destination;
 769         smsg.msg_namelen = sizeof(struct sockaddr_nl);
 770         count = sendmsg(udev_monitor->sock, &smsg, 0);
 771         if (count < 0) {
 772                 if (!destination && errno == ECONNREFUSED) {
 773                         log_debug("passed device to netlink monitor %p", udev_monitor);
 774                         return 0;
 775                 } else
 776                         return -errno;
 777         }
 778
 779         log_debug("passed %zi byte device to netlink monitor %p", count, udev_monitor);
 780         return count;
 781 }
 782
 783 /**
 784  * udev_monitor_filter_add_match_subsystem_devtype:
 785  * @udev_monitor: the monitor
 786  * @subsystem: the subsystem value to match the incoming devices against
 787  * @devtype: the devtype value to match the incoming devices against
 788  *
 789  * This filter is efficiently executed inside the kernel, and libudev subscribers
 790  * will usually not be woken up for devices which do not match.
 791  *
 792  * The filter must be installed before the monitor is switched to listening mode.
 793  *
 794  * Returns: 0 on success, otherwise a negative error value.
 795  */
 796 _public_ int udev_monitor_filter_add_match_subsystem_devtype(struct udev_monitor *udev_monitor, const char *subsystem, const char *devtype)
 797 {
 798         if (udev_monitor == NULL)
 799                 return -EINVAL;
 800         if (subsystem == NULL)
 801                 return -EINVAL;
 802         if (udev_list_entry_add(&udev_monitor->filter_subsystem_list, subsystem, devtype) == NULL)
 803                 return -ENOMEM;
 804         return 0;
 805 }
 806
 807 /**
 808  * udev_monitor_filter_add_match_tag:
 809  * @udev_monitor: the monitor
 810  * @tag: the name of a tag
 811  *
 812  * This filter is efficiently executed inside the kernel, and libudev subscribers
 813  * will usually not be woken up for devices which do not match.
 814  *
 815  * The filter must be installed before the monitor is switched to listening mode.
 816  *
 817  * Returns: 0 on success, otherwise a negative error value.
 818  */
 819 _public_ int udev_monitor_filter_add_match_tag(struct udev_monitor *udev_monitor, const char *tag)
 820 {
 821         if (udev_monitor == NULL)
 822                 return -EINVAL;
 823         if (tag == NULL)
 824                 return -EINVAL;
 825         if (udev_list_entry_add(&udev_monitor->filter_tag_list, tag, NULL) == NULL)
 826                 return -ENOMEM;
 827         return 0;
 828 }
 829
 830 /**
 831  * udev_monitor_filter_remove:
 832  * @udev_monitor: monitor
 833  *
 834  * Remove all filters from monitor.
 835  *
 836  * Returns: 0 on success, otherwise a negative error value.
 837  */
 838 _public_ int udev_monitor_filter_remove(struct udev_monitor *udev_monitor)
 839 {
 840         static struct sock_fprog filter = { 0, NULL };
 841
 842         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
 843         return setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter));
 844 }