src/libudev/libudev-monitor.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <linux/filter.h>
   5 #include <linux/netlink.h>
   6 #include <poll.h>
   7 #include <stddef.h>
   8 #include <stdio.h>
   9 #include <stdlib.h>
  10 #include <string.h>
  11 #include <sys/socket.h>
  12 #include <unistd.h>
  13
  14 #include "libudev.h"
  15
  16 #include "alloc-util.h"
  17 #include "fd-util.h"
  18 #include "fileio.h"
  19 #include "format-util.h"
  20 #include "libudev-private.h"
  21 #include "missing.h"
  22 #include "mount-util.h"
  23 #include "socket-util.h"
  24 #include "string-util.h"
  25
  26 /**
  27  * SECTION:libudev-monitor
  28  * @short_description: device event source
  29  *
  30  * Connects to a device event source.
  31  */
  32
  33 /**
  34  * udev_monitor:
  35  *
  36  * Opaque object handling an event source.
  37  */
  38 struct udev_monitor {
  39         struct udev *udev;
  40         int refcount;
  41         int sock;
  42         union sockaddr_union snl;
  43         union sockaddr_union snl_trusted_sender;
  44         union sockaddr_union snl_destination;
  45         socklen_t addrlen;
  46         struct udev_list filter_subsystem_list;
  47         struct udev_list filter_tag_list;
  48         bool bound;
  49 };
  50
  51 enum udev_monitor_netlink_group {
  52         UDEV_MONITOR_NONE,
  53         UDEV_MONITOR_KERNEL,
  54         UDEV_MONITOR_UDEV,
  55 };
  56
  57 #define UDEV_MONITOR_MAGIC                0xfeedcafe
  58 struct udev_monitor_netlink_header {
  59         /* "libudev" prefix to distinguish libudev and kernel messages */
  60         char prefix[8];
  61         /*
  62          * magic to protect against daemon <-> library message format mismatch
  63          * used in the kernel from socket filter rules; needs to be stored in network order
  64          */
  65         unsigned int magic;
  66         /* total length of header structure known to the sender */
  67         unsigned int header_size;
  68         /* properties string buffer */
  69         unsigned int properties_off;
  70         unsigned int properties_len;
  71         /*
  72          * hashes of primary device properties strings, to let libudev subscribers
  73          * use in-kernel socket filters; values need to be stored in network order
  74          */
  75         unsigned int filter_subsystem_hash;
  76         unsigned int filter_devtype_hash;
  77         unsigned int filter_tag_bloom_hi;
  78         unsigned int filter_tag_bloom_lo;
  79 };
  80
  81 static struct udev_monitor *udev_monitor_new(struct udev *udev) {
  82         struct udev_monitor *udev_monitor;
  83
  84         udev_monitor = new0(struct udev_monitor, 1);
  85         if (udev_monitor == NULL) {
  86                 errno = ENOMEM;
  87                 return NULL;
  88         }
  89         udev_monitor->refcount = 1;
  90         udev_monitor->udev = udev;
  91         udev_list_init(udev, &udev_monitor->filter_subsystem_list, false);
  92         udev_list_init(udev, &udev_monitor->filter_tag_list, true);
  93         return udev_monitor;
  94 }
  95
  96 /* we consider udev running when /dev is on devtmpfs */
  97 static bool udev_has_devtmpfs(struct udev *udev) {
  98
  99         _cleanup_fclose_ FILE *f = NULL;
 100         char line[LINE_MAX], *e;
 101         int mount_id, r;
 102
 103         r = path_get_mnt_id("/dev", &mount_id);
 104         if (r < 0) {
 105                 if (r != -EOPNOTSUPP)
 106                         log_debug_errno(r, "name_to_handle_at on /dev: %m");
 107
 108                 return false;
 109         }
 110
 111         f = fopen("/proc/self/mountinfo", "re");
 112         if (!f)
 113                 return false;
 114
 115         FOREACH_LINE(line, f, return false) {
 116                 int mid;
 117
 118                 if (sscanf(line, "%i", &mid) != 1)
 119                         continue;
 120
 121                 if (mid != mount_id)
 122                         continue;
 123
 124                 e = strstr(line, " - ");
 125                 if (!e)
 126                         continue;
 127
 128                 /* accept any name that starts with the currently expected type */
 129                 if (startswith(e + 3, "devtmpfs"))
 130                         return true;
 131         }
 132
 133         return false;
 134 }
 135
 136 static void monitor_set_nl_address(struct udev_monitor *udev_monitor) {
 137         union sockaddr_union snl;
 138         socklen_t addrlen;
 139         int r;
 140
 141         assert(udev_monitor);
 142
 143         /* get the address the kernel has assigned us
 144          * it is usually, but not necessarily the pid
 145          */
 146         addrlen = sizeof(struct sockaddr_nl);
 147         r = getsockname(udev_monitor->sock, &snl.sa, &addrlen);
 148         if (r >= 0)
 149                 udev_monitor->snl.nl.nl_pid = snl.nl.nl_pid;
 150 }
 151
 152 struct udev_monitor *udev_monitor_new_from_netlink_fd(struct udev *udev, const char *name, int fd) {
 153         struct udev_monitor *udev_monitor;
 154         unsigned int group;
 155
 156         if (udev == NULL) {
 157                 errno = EINVAL;
 158                 return NULL;
 159         }
 160
 161         if (name == NULL)
 162                 group = UDEV_MONITOR_NONE;
 163         else if (streq(name, "udev")) {
 164                 /*
 165                  * We do not support subscribing to uevents if no instance of
 166                  * udev is running. Uevents would otherwise broadcast the
 167                  * processing data of the host into containers, which is not
 168                  * desired.
 169                  *
 170                  * Containers will currently not get any udev uevents, until
 171                  * a supporting infrastructure is available.
 172                  *
 173                  * We do not set a netlink multicast group here, so the socket
 174                  * will not receive any messages.
 175                  */
 176                 if (access("/run/udev/control", F_OK) < 0 && !udev_has_devtmpfs(udev)) {
 177                         log_debug("the udev service seems not to be active, disable the monitor");
 178                         group = UDEV_MONITOR_NONE;
 179                 } else
 180                         group = UDEV_MONITOR_UDEV;
 181         } else if (streq(name, "kernel"))
 182                 group = UDEV_MONITOR_KERNEL;
 183         else {
 184                 errno = EINVAL;
 185                 return NULL;
 186         }
 187
 188         udev_monitor = udev_monitor_new(udev);
 189         if (udev_monitor == NULL)
 190                 return NULL;
 191
 192         if (fd < 0) {
 193                 udev_monitor->sock = socket(PF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_KOBJECT_UEVENT);
 194                 if (udev_monitor->sock < 0) {
 195                         log_debug_errno(errno, "error getting socket: %m");
 196                         return mfree(udev_monitor);
 197                 }
 198         } else {
 199                 udev_monitor->bound = true;
 200                 udev_monitor->sock = fd;
 201                 monitor_set_nl_address(udev_monitor);
 202         }
 203
 204         udev_monitor->snl.nl.nl_family = AF_NETLINK;
 205         udev_monitor->snl.nl.nl_groups = group;
 206
 207         /* default destination for sending */
 208         udev_monitor->snl_destination.nl.nl_family = AF_NETLINK;
 209         udev_monitor->snl_destination.nl.nl_groups = UDEV_MONITOR_UDEV;
 210
 211         return udev_monitor;
 212 }
 213
 214 /**
 215  * udev_monitor_new_from_netlink:
 216  * @udev: udev library context
 217  * @name: name of event source
 218  *
 219  * Create new udev monitor and connect to a specified event
 220  * source. Valid sources identifiers are "udev" and "kernel".
 221  *
 222  * Applications should usually not connect directly to the
 223  * "kernel" events, because the devices might not be useable
 224  * at that time, before udev has configured them, and created
 225  * device nodes. Accessing devices at the same time as udev,
 226  * might result in unpredictable behavior. The "udev" events
 227  * are sent out after udev has finished its event processing,
 228  * all rules have been processed, and needed device nodes are
 229  * created.
 230  *
 231  * The initial refcount is 1, and needs to be decremented to
 232  * release the resources of the udev monitor.
 233  *
 234  * Returns: a new udev monitor, or #NULL, in case of an error
 235  **/
 236 _public_ struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev, const char *name) {
 237         return udev_monitor_new_from_netlink_fd(udev, name, -1);
 238 }
 239
 240 static inline void bpf_stmt(struct sock_filter *inss, unsigned int *i,
 241                             unsigned short code, unsigned int data)
 242 {
 243         struct sock_filter *ins = &inss[*i];
 244
 245         ins->code = code;
 246         ins->k = data;
 247         (*i)++;
 248 }
 249
 250 static inline void bpf_jmp(struct sock_filter *inss, unsigned int *i,
 251                            unsigned short code, unsigned int data,
 252                            unsigned short jt, unsigned short jf)
 253 {
 254         struct sock_filter *ins = &inss[*i];
 255
 256         ins->code = code;
 257         ins->jt = jt;
 258         ins->jf = jf;
 259         ins->k = data;
 260         (*i)++;
 261 }
 262
 263 /**
 264  * udev_monitor_filter_update:
 265  * @udev_monitor: monitor
 266  *
 267  * Update the installed socket filter. This is only needed,
 268  * if the filter was removed or changed.
 269  *
 270  * Returns: 0 on success, otherwise a negative error value.
 271  */
 272 _public_ int udev_monitor_filter_update(struct udev_monitor *udev_monitor)
 273 {
 274         struct sock_filter ins[512];
 275         struct sock_fprog filter;
 276         unsigned int i;
 277         struct udev_list_entry *list_entry;
 278         int err;
 279
 280         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL &&
 281             udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
 282                 return 0;
 283
 284         memzero(ins, sizeof(ins));
 285         i = 0;
 286
 287         /* load magic in A */
 288         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, magic));
 289         /* jump if magic matches */
 290         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, UDEV_MONITOR_MAGIC, 1, 0);
 291         /* wrong magic, pass packet */
 292         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 293
 294         if (udev_list_get_entry(&udev_monitor->filter_tag_list) != NULL) {
 295                 int tag_matches;
 296
 297                 /* count tag matches, to calculate end of tag match block */
 298                 tag_matches = 0;
 299                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list))
 300                         tag_matches++;
 301
 302                 /* add all tags matches */
 303                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
 304                         uint64_t tag_bloom_bits = util_string_bloom64(udev_list_entry_get_name(list_entry));
 305                         uint32_t tag_bloom_hi = tag_bloom_bits >> 32;
 306                         uint32_t tag_bloom_lo = tag_bloom_bits & 0xffffffff;
 307
 308                         /* load device bloom bits in A */
 309                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_hi));
 310                         /* clear bits (tag bits & bloom bits) */
 311                         bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_hi);
 312                         /* jump to next tag if it does not match */
 313                         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_hi, 0, 3);
 314
 315                         /* load device bloom bits in A */
 316                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_lo));
 317                         /* clear bits (tag bits & bloom bits) */
 318                         bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_lo);
 319                         /* jump behind end of tag match block if tag matches */
 320                         tag_matches--;
 321                         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_lo, 1 + (tag_matches * 6), 0);
 322                 }
 323
 324                 /* nothing matched, drop packet */
 325                 bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
 326         }
 327
 328         /* add all subsystem matches */
 329         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) != NULL) {
 330                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
 331                         unsigned int hash = util_string_hash32(udev_list_entry_get_name(list_entry));
 332
 333                         /* load device subsystem value in A */
 334                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_subsystem_hash));
 335                         if (udev_list_entry_get_value(list_entry) == NULL) {
 336                                 /* jump if subsystem does not match */
 337                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
 338                         } else {
 339                                 /* jump if subsystem does not match */
 340                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 3);
 341
 342                                 /* load device devtype value in A */
 343                                 bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_devtype_hash));
 344                                 /* jump if value does not match */
 345                                 hash = util_string_hash32(udev_list_entry_get_value(list_entry));
 346                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
 347                         }
 348
 349                         /* matched, pass packet */
 350                         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 351
 352                         if (i+1 >= ELEMENTSOF(ins))
 353                                 return -E2BIG;
 354                 }
 355
 356                 /* nothing matched, drop packet */
 357                 bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
 358         }
 359
 360         /* matched, pass packet */
 361         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 362
 363         /* install filter */
 364         memzero(&filter, sizeof(filter));
 365         filter.len = i;
 366         filter.filter = ins;
 367         err = setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter));
 368         return err < 0 ? -errno : 0;
 369 }
 370
 371 int udev_monitor_allow_unicast_sender(struct udev_monitor *udev_monitor, struct udev_monitor *sender)
 372 {
 373         udev_monitor->snl_trusted_sender.nl.nl_pid = sender->snl.nl.nl_pid;
 374         return 0;
 375 }
 376
 377 /**
 378  * udev_monitor_enable_receiving:
 379  * @udev_monitor: the monitor which should receive events
 380  *
 381  * Binds the @udev_monitor socket to the event source.
 382  *
 383  * Returns: 0 on success, otherwise a negative error value.
 384  */
 385 _public_ int udev_monitor_enable_receiving(struct udev_monitor *udev_monitor)
 386 {
 387         int err = 0;
 388         const int on = 1;
 389
 390         udev_monitor_filter_update(udev_monitor);
 391
 392         if (!udev_monitor->bound) {
 393                 err = bind(udev_monitor->sock,
 394                            &udev_monitor->snl.sa, sizeof(struct sockaddr_nl));
 395                 if (err == 0)
 396                         udev_monitor->bound = true;
 397         }
 398
 399         if (err >= 0)
 400                 monitor_set_nl_address(udev_monitor);
 401         else
 402                 return log_debug_errno(errno, "bind failed: %m");
 403
 404         /* enable receiving of sender credentials */
 405         err = setsockopt(udev_monitor->sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
 406         if (err < 0)
 407                 log_debug_errno(errno, "setting SO_PASSCRED failed: %m");
 408
 409         return 0;
 410 }
 411
 412 /**
 413  * udev_monitor_set_receive_buffer_size:
 414  * @udev_monitor: the monitor which should receive events
 415  * @size: the size in bytes
 416  *
 417  * Set the size of the kernel socket buffer. This call needs the
 418  * appropriate privileges to succeed.
 419  *
 420  * Returns: 0 on success, otherwise -1 on error.
 421  */
 422 _public_ int udev_monitor_set_receive_buffer_size(struct udev_monitor *udev_monitor, int size)
 423 {
 424         if (udev_monitor == NULL)
 425                 return -EINVAL;
 426         if (setsockopt(udev_monitor->sock, SOL_SOCKET, SO_RCVBUFFORCE, &size, sizeof(size)) < 0)
 427                 return -errno;
 428
 429         return 0;
 430 }
 431
 432 int udev_monitor_disconnect(struct udev_monitor *udev_monitor)
 433 {
 434         int err;
 435
 436         err = close(udev_monitor->sock);
 437         udev_monitor->sock = -1;
 438         return err < 0 ? -errno : 0;
 439 }
 440
 441 /**
 442  * udev_monitor_ref:
 443  * @udev_monitor: udev monitor
 444  *
 445  * Take a reference of a udev monitor.
 446  *
 447  * Returns: the passed udev monitor
 448  **/
 449 _public_ struct udev_monitor *udev_monitor_ref(struct udev_monitor *udev_monitor)
 450 {
 451         if (udev_monitor == NULL)
 452                 return NULL;
 453         udev_monitor->refcount++;
 454         return udev_monitor;
 455 }
 456
 457 /**
 458  * udev_monitor_unref:
 459  * @udev_monitor: udev monitor
 460  *
 461  * Drop a reference of a udev monitor. If the refcount reaches zero,
 462  * the bound socket will be closed, and the resources of the monitor
 463  * will be released.
 464  *
 465  * Returns: #NULL
 466  **/
 467 _public_ struct udev_monitor *udev_monitor_unref(struct udev_monitor *udev_monitor)
 468 {
 469         if (udev_monitor == NULL)
 470                 return NULL;
 471         udev_monitor->refcount--;
 472         if (udev_monitor->refcount > 0)
 473                 return NULL;
 474         if (udev_monitor->sock >= 0)
 475                 close(udev_monitor->sock);
 476         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
 477         udev_list_cleanup(&udev_monitor->filter_tag_list);
 478         return mfree(udev_monitor);
 479 }
 480
 481 /**
 482  * udev_monitor_get_udev:
 483  * @udev_monitor: udev monitor
 484  *
 485  * Retrieve the udev library context the monitor was created with.
 486  *
 487  * Returns: the udev library context
 488  **/
 489 _public_ struct udev *udev_monitor_get_udev(struct udev_monitor *udev_monitor)
 490 {
 491         if (udev_monitor == NULL)
 492                 return NULL;
 493         return udev_monitor->udev;
 494 }
 495
 496 /**
 497  * udev_monitor_get_fd:
 498  * @udev_monitor: udev monitor
 499  *
 500  * Retrieve the socket file descriptor associated with the monitor.
 501  *
 502  * Returns: the socket file descriptor
 503  **/
 504 _public_ int udev_monitor_get_fd(struct udev_monitor *udev_monitor)
 505 {
 506         if (udev_monitor == NULL)
 507                 return -EINVAL;
 508         return udev_monitor->sock;
 509 }
 510
 511 static int passes_filter(struct udev_monitor *udev_monitor, struct udev_device *udev_device)
 512 {
 513         struct udev_list_entry *list_entry;
 514
 515         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL)
 516                 goto tag;
 517         udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
 518                 const char *subsys = udev_list_entry_get_name(list_entry);
 519                 const char *dsubsys = udev_device_get_subsystem(udev_device);
 520                 const char *devtype;
 521                 const char *ddevtype;
 522
 523                 if (!streq(dsubsys, subsys))
 524                         continue;
 525
 526                 devtype = udev_list_entry_get_value(list_entry);
 527                 if (devtype == NULL)
 528                         goto tag;
 529                 ddevtype = udev_device_get_devtype(udev_device);
 530                 if (ddevtype == NULL)
 531                         continue;
 532                 if (streq(ddevtype, devtype))
 533                         goto tag;
 534         }
 535         return 0;
 536
 537 tag:
 538         if (udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
 539                 return 1;
 540         udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
 541                 const char *tag = udev_list_entry_get_name(list_entry);
 542
 543                 if (udev_device_has_tag(udev_device, tag))
 544                         return 1;
 545         }
 546         return 0;
 547 }
 548
 549 /**
 550  * udev_monitor_receive_device:
 551  * @udev_monitor: udev monitor
 552  *
 553  * Receive data from the udev monitor socket, allocate a new udev
 554  * device, fill in the received data, and return the device.
 555  *
 556  * Only socket connections with uid=0 are accepted.
 557  *
 558  * The monitor socket is by default set to NONBLOCK. A variant of poll() on
 559  * the file descriptor returned by udev_monitor_get_fd() should to be used to
 560  * wake up when new devices arrive, or alternatively the file descriptor
 561  * switched into blocking mode.
 562  *
 563  * The initial refcount is 1, and needs to be decremented to
 564  * release the resources of the udev device.
 565  *
 566  * Returns: a new udev device, or #NULL, in case of an error
 567  **/
 568 _public_ struct udev_device *udev_monitor_receive_device(struct udev_monitor *udev_monitor)
 569 {
 570         struct udev_device *udev_device;
 571         struct msghdr smsg;
 572         struct iovec iov;
 573         char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
 574         struct cmsghdr *cmsg;
 575         union sockaddr_union snl;
 576         struct ucred *cred;
 577         union {
 578                 struct udev_monitor_netlink_header nlh;
 579                 char raw[8192];
 580         } buf;
 581         ssize_t buflen;
 582         ssize_t bufpos;
 583         bool is_initialized = false;
 584
 585 retry:
 586         if (udev_monitor == NULL) {
 587                 errno = EINVAL;
 588                 return NULL;
 589         }
 590         iov.iov_base = &buf;
 591         iov.iov_len = sizeof(buf);
 592         memzero(&smsg, sizeof(struct msghdr));
 593         smsg.msg_iov = &iov;
 594         smsg.msg_iovlen = 1;
 595         smsg.msg_control = cred_msg;
 596         smsg.msg_controllen = sizeof(cred_msg);
 597         smsg.msg_name = &snl;
 598         smsg.msg_namelen = sizeof(snl);
 599
 600         buflen = recvmsg(udev_monitor->sock, &smsg, 0);
 601         if (buflen < 0) {
 602                 if (errno != EINTR)
 603                         log_debug("unable to receive message");
 604                 return NULL;
 605         }
 606
 607         if (buflen < 32 || (smsg.msg_flags & MSG_TRUNC)) {
 608                 log_debug("invalid message length");
 609                 errno = EINVAL;
 610                 return NULL;
 611         }
 612
 613         if (snl.nl.nl_groups == 0) {
 614                 /* unicast message, check if we trust the sender */
 615                 if (udev_monitor->snl_trusted_sender.nl.nl_pid == 0 ||
 616                     snl.nl.nl_pid != udev_monitor->snl_trusted_sender.nl.nl_pid) {
 617                         log_debug("unicast netlink message ignored");
 618                         errno = EAGAIN;
 619                         return NULL;
 620                 }
 621         } else if (snl.nl.nl_groups == UDEV_MONITOR_KERNEL) {
 622                 if (snl.nl.nl_pid > 0) {
 623                         log_debug("multicast kernel netlink message from PID %"PRIu32" ignored",
 624                                   snl.nl.nl_pid);
 625                         errno = EAGAIN;
 626                         return NULL;
 627                 }
 628         }
 629
 630         cmsg = CMSG_FIRSTHDR(&smsg);
 631         if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
 632                 log_debug("no sender credentials received, message ignored");
 633                 errno = EAGAIN;
 634                 return NULL;
 635         }
 636
 637         cred = (struct ucred *)CMSG_DATA(cmsg);
 638         if (cred->uid != 0) {
 639                 log_debug("sender uid="UID_FMT", message ignored", cred->uid);
 640                 errno = EAGAIN;
 641                 return NULL;
 642         }
 643
 644         if (memcmp(buf.raw, "libudev", 8) == 0) {
 645                 /* udev message needs proper version magic */
 646                 if (buf.nlh.magic != htobe32(UDEV_MONITOR_MAGIC)) {
 647                         log_debug("unrecognized message signature (%x != %x)",
 648                                  buf.nlh.magic, htobe32(UDEV_MONITOR_MAGIC));
 649                         errno = EAGAIN;
 650                         return NULL;
 651                 }
 652                 if (buf.nlh.properties_off+32 > (size_t)buflen) {
 653                         log_debug("message smaller than expected (%u > %zd)",
 654                                   buf.nlh.properties_off+32, buflen);
 655                         errno = EAGAIN;
 656                         return NULL;
 657                 }
 658
 659                 bufpos = buf.nlh.properties_off;
 660
 661                 /* devices received from udev are always initialized */
 662                 is_initialized = true;
 663         } else {
 664                 /* kernel message with header */
 665                 bufpos = strlen(buf.raw) + 1;
 666                 if ((size_t)bufpos < sizeof("a@/d") || bufpos >= buflen) {
 667                         log_debug("invalid message length");
 668                         errno = EAGAIN;
 669                         return NULL;
 670                 }
 671
 672                 /* check message header */
 673                 if (strstr(buf.raw, "@/") == NULL) {
 674                         log_debug("unrecognized message header");
 675                         errno = EAGAIN;
 676                         return NULL;
 677                 }
 678         }
 679
 680         udev_device = udev_device_new_from_nulstr(udev_monitor->udev, &buf.raw[bufpos], buflen - bufpos);
 681         if (!udev_device) {
 682                 log_debug_errno(errno, "could not create device: %m");
 683                 return NULL;
 684         }
 685
 686         if (is_initialized)
 687                 udev_device_set_is_initialized(udev_device);
 688
 689         /* skip device, if it does not pass the current filter */
 690         if (!passes_filter(udev_monitor, udev_device)) {
 691                 struct pollfd pfd[1];
 692                 int rc;
 693
 694                 udev_device_unref(udev_device);
 695
 696                 /* if something is queued, get next device */
 697                 pfd[0].fd = udev_monitor->sock;
 698                 pfd[0].events = POLLIN;
 699                 rc = poll(pfd, 1, 0);
 700                 if (rc > 0)
 701                         goto retry;
 702
 703                 errno = EAGAIN;
 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 const struct sock_fprog filter = { 0, NULL };
 841
 842         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
 843         if (setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter)) < 0)
 844                 return -errno;
 845
 846         return 0;
 847 }