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 "libudev-device-internal.h"
  22 #include "missing.h"
  23 #include "mount-util.h"
  24 #include "socket-util.h"
  25 #include "string-util.h"
  26
  27 /**
  28  * SECTION:libudev-monitor
  29  * @short_description: device event source
  30  *
  31  * Connects to a device event source.
  32  */
  33
  34 /**
  35  * udev_monitor:
  36  *
  37  * Opaque object handling an event source.
  38  */
  39 struct udev_monitor {
  40         struct udev *udev;
  41         int refcount;
  42         int sock;
  43         union sockaddr_union snl;
  44         union sockaddr_union snl_trusted_sender;
  45         union sockaddr_union snl_destination;
  46         socklen_t addrlen;
  47         struct udev_list filter_subsystem_list;
  48         struct udev_list filter_tag_list;
  49         bool bound;
  50 };
  51
  52 enum udev_monitor_netlink_group {
  53         UDEV_MONITOR_NONE,
  54         UDEV_MONITOR_KERNEL,
  55         UDEV_MONITOR_UDEV,
  56 };
  57
  58 #define UDEV_MONITOR_MAGIC                0xfeedcafe
  59 struct udev_monitor_netlink_header {
  60         /* "libudev" prefix to distinguish libudev and kernel messages */
  61         char prefix[8];
  62         /*
  63          * magic to protect against daemon <-> library message format mismatch
  64          * used in the kernel from socket filter rules; needs to be stored in network order
  65          */
  66         unsigned int magic;
  67         /* total length of header structure known to the sender */
  68         unsigned int header_size;
  69         /* properties string buffer */
  70         unsigned int properties_off;
  71         unsigned int properties_len;
  72         /*
  73          * hashes of primary device properties strings, to let libudev subscribers
  74          * use in-kernel socket filters; values need to be stored in network order
  75          */
  76         unsigned int filter_subsystem_hash;
  77         unsigned int filter_devtype_hash;
  78         unsigned int filter_tag_bloom_hi;
  79         unsigned int filter_tag_bloom_lo;
  80 };
  81
  82 static struct udev_monitor *udev_monitor_new(struct udev *udev) {
  83         struct udev_monitor *udev_monitor;
  84
  85         udev_monitor = new0(struct udev_monitor, 1);
  86         if (udev_monitor == NULL) {
  87                 errno = ENOMEM;
  88                 return NULL;
  89         }
  90         udev_monitor->refcount = 1;
  91         udev_monitor->udev = udev;
  92         udev_list_init(udev, &udev_monitor->filter_subsystem_list, false);
  93         udev_list_init(udev, &udev_monitor->filter_tag_list, true);
  94         return udev_monitor;
  95 }
  96
  97 /* we consider udev running when /dev is on devtmpfs */
  98 static bool udev_has_devtmpfs(struct udev *udev) {
  99
 100         _cleanup_fclose_ FILE *f = NULL;
 101         char line[LINE_MAX], *e;
 102         int mount_id, r;
 103
 104         r = path_get_mnt_id("/dev", &mount_id);
 105         if (r < 0) {
 106                 if (r != -EOPNOTSUPP)
 107                         log_debug_errno(r, "name_to_handle_at on /dev: %m");
 108
 109                 return false;
 110         }
 111
 112         f = fopen("/proc/self/mountinfo", "re");
 113         if (!f)
 114                 return false;
 115
 116         FOREACH_LINE(line, f, return false) {
 117                 int mid;
 118
 119                 if (sscanf(line, "%i", &mid) != 1)
 120                         continue;
 121
 122                 if (mid != mount_id)
 123                         continue;
 124
 125                 e = strstr(line, " - ");
 126                 if (!e)
 127                         continue;
 128
 129                 /* accept any name that starts with the currently expected type */
 130                 if (startswith(e + 3, "devtmpfs"))
 131                         return true;
 132         }
 133
 134         return false;
 135 }
 136
 137 static void monitor_set_nl_address(struct udev_monitor *udev_monitor) {
 138         union sockaddr_union snl;
 139         socklen_t addrlen;
 140         int r;
 141
 142         assert(udev_monitor);
 143
 144         /* get the address the kernel has assigned us
 145          * it is usually, but not necessarily the pid
 146          */
 147         addrlen = sizeof(struct sockaddr_nl);
 148         r = getsockname(udev_monitor->sock, &snl.sa, &addrlen);
 149         if (r >= 0)
 150                 udev_monitor->snl.nl.nl_pid = snl.nl.nl_pid;
 151 }
 152
 153 struct udev_monitor *udev_monitor_new_from_netlink_fd(struct udev *udev, const char *name, int fd) {
 154         struct udev_monitor *udev_monitor;
 155         unsigned int group;
 156
 157         if (name == NULL)
 158                 group = UDEV_MONITOR_NONE;
 159         else if (streq(name, "udev")) {
 160                 /*
 161                  * We do not support subscribing to uevents if no instance of
 162                  * udev is running. Uevents would otherwise broadcast the
 163                  * processing data of the host into containers, which is not
 164                  * desired.
 165                  *
 166                  * Containers will currently not get any udev uevents, until
 167                  * a supporting infrastructure is available.
 168                  *
 169                  * We do not set a netlink multicast group here, so the socket
 170                  * will not receive any messages.
 171                  */
 172                 if (access("/run/udev/control", F_OK) < 0 && !udev_has_devtmpfs(udev)) {
 173                         log_debug("the udev service seems not to be active, disable the monitor");
 174                         group = UDEV_MONITOR_NONE;
 175                 } else
 176                         group = UDEV_MONITOR_UDEV;
 177         } else if (streq(name, "kernel"))
 178                 group = UDEV_MONITOR_KERNEL;
 179         else {
 180                 errno = EINVAL;
 181                 return NULL;
 182         }
 183
 184         udev_monitor = udev_monitor_new(udev);
 185         if (udev_monitor == NULL)
 186                 return NULL;
 187
 188         if (fd < 0) {
 189                 udev_monitor->sock = socket(PF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_KOBJECT_UEVENT);
 190                 if (udev_monitor->sock < 0) {
 191                         log_debug_errno(errno, "error getting socket: %m");
 192                         return mfree(udev_monitor);
 193                 }
 194         } else {
 195                 udev_monitor->bound = true;
 196                 udev_monitor->sock = fd;
 197                 monitor_set_nl_address(udev_monitor);
 198         }
 199
 200         udev_monitor->snl.nl.nl_family = AF_NETLINK;
 201         udev_monitor->snl.nl.nl_groups = group;
 202
 203         /* default destination for sending */
 204         udev_monitor->snl_destination.nl.nl_family = AF_NETLINK;
 205         udev_monitor->snl_destination.nl.nl_groups = UDEV_MONITOR_UDEV;
 206
 207         return udev_monitor;
 208 }
 209
 210 /**
 211  * udev_monitor_new_from_netlink:
 212  * @udev: udev library context
 213  * @name: name of event source
 214  *
 215  * Create new udev monitor and connect to a specified event
 216  * source. Valid sources identifiers are "udev" and "kernel".
 217  *
 218  * Applications should usually not connect directly to the
 219  * "kernel" events, because the devices might not be useable
 220  * at that time, before udev has configured them, and created
 221  * device nodes. Accessing devices at the same time as udev,
 222  * might result in unpredictable behavior. The "udev" events
 223  * are sent out after udev has finished its event processing,
 224  * all rules have been processed, and needed device nodes are
 225  * created.
 226  *
 227  * The initial refcount is 1, and needs to be decremented to
 228  * release the resources of the udev monitor.
 229  *
 230  * Returns: a new udev monitor, or #NULL, in case of an error
 231  **/
 232 _public_ struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev, const char *name) {
 233         return udev_monitor_new_from_netlink_fd(udev, name, -1);
 234 }
 235
 236 static inline void bpf_stmt(struct sock_filter *inss, unsigned int *i,
 237                             unsigned short code, unsigned int data)
 238 {
 239         struct sock_filter *ins = &inss[*i];
 240
 241         ins->code = code;
 242         ins->k = data;
 243         (*i)++;
 244 }
 245
 246 static inline void bpf_jmp(struct sock_filter *inss, unsigned int *i,
 247                            unsigned short code, unsigned int data,
 248                            unsigned short jt, unsigned short jf)
 249 {
 250         struct sock_filter *ins = &inss[*i];
 251
 252         ins->code = code;
 253         ins->jt = jt;
 254         ins->jf = jf;
 255         ins->k = data;
 256         (*i)++;
 257 }
 258
 259 /**
 260  * udev_monitor_filter_update:
 261  * @udev_monitor: monitor
 262  *
 263  * Update the installed socket filter. This is only needed,
 264  * if the filter was removed or changed.
 265  *
 266  * Returns: 0 on success, otherwise a negative error value.
 267  */
 268 _public_ int udev_monitor_filter_update(struct udev_monitor *udev_monitor)
 269 {
 270         struct sock_filter ins[512];
 271         struct sock_fprog filter;
 272         unsigned int i;
 273         struct udev_list_entry *list_entry;
 274         int err;
 275
 276         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL &&
 277             udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
 278                 return 0;
 279
 280         memzero(ins, sizeof(ins));
 281         i = 0;
 282
 283         /* load magic in A */
 284         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, magic));
 285         /* jump if magic matches */
 286         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, UDEV_MONITOR_MAGIC, 1, 0);
 287         /* wrong magic, pass packet */
 288         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 289
 290         if (udev_list_get_entry(&udev_monitor->filter_tag_list) != NULL) {
 291                 int tag_matches;
 292
 293                 /* count tag matches, to calculate end of tag match block */
 294                 tag_matches = 0;
 295                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list))
 296                         tag_matches++;
 297
 298                 /* add all tags matches */
 299                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
 300                         uint64_t tag_bloom_bits = util_string_bloom64(udev_list_entry_get_name(list_entry));
 301                         uint32_t tag_bloom_hi = tag_bloom_bits >> 32;
 302                         uint32_t tag_bloom_lo = tag_bloom_bits & 0xffffffff;
 303
 304                         /* load device bloom bits in A */
 305                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_hi));
 306                         /* clear bits (tag bits & bloom bits) */
 307                         bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_hi);
 308                         /* jump to next tag if it does not match */
 309                         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_hi, 0, 3);
 310
 311                         /* load device bloom bits in A */
 312                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_lo));
 313                         /* clear bits (tag bits & bloom bits) */
 314                         bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_lo);
 315                         /* jump behind end of tag match block if tag matches */
 316                         tag_matches--;
 317                         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_lo, 1 + (tag_matches * 6), 0);
 318                 }
 319
 320                 /* nothing matched, drop packet */
 321                 bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
 322         }
 323
 324         /* add all subsystem matches */
 325         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) != NULL) {
 326                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
 327                         unsigned int hash = util_string_hash32(udev_list_entry_get_name(list_entry));
 328
 329                         /* load device subsystem value in A */
 330                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_subsystem_hash));
 331                         if (udev_list_entry_get_value(list_entry) == NULL) {
 332                                 /* jump if subsystem does not match */
 333                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
 334                         } else {
 335                                 /* jump if subsystem does not match */
 336                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 3);
 337
 338                                 /* load device devtype value in A */
 339                                 bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_devtype_hash));
 340                                 /* jump if value does not match */
 341                                 hash = util_string_hash32(udev_list_entry_get_value(list_entry));
 342                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
 343                         }
 344
 345                         /* matched, pass packet */
 346                         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 347
 348                         if (i+1 >= ELEMENTSOF(ins))
 349                                 return -E2BIG;
 350                 }
 351
 352                 /* nothing matched, drop packet */
 353                 bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
 354         }
 355
 356         /* matched, pass packet */
 357         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 358
 359         /* install filter */
 360         memzero(&filter, sizeof(filter));
 361         filter.len = i;
 362         filter.filter = ins;
 363         err = setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter));
 364         return err < 0 ? -errno : 0;
 365 }
 366
 367 int udev_monitor_allow_unicast_sender(struct udev_monitor *udev_monitor, struct udev_monitor *sender)
 368 {
 369         udev_monitor->snl_trusted_sender.nl.nl_pid = sender->snl.nl.nl_pid;
 370         return 0;
 371 }
 372
 373 /**
 374  * udev_monitor_enable_receiving:
 375  * @udev_monitor: the monitor which should receive events
 376  *
 377  * Binds the @udev_monitor socket to the event source.
 378  *
 379  * Returns: 0 on success, otherwise a negative error value.
 380  */
 381 _public_ int udev_monitor_enable_receiving(struct udev_monitor *udev_monitor)
 382 {
 383         int err = 0;
 384         const int on = 1;
 385
 386         udev_monitor_filter_update(udev_monitor);
 387
 388         if (!udev_monitor->bound) {
 389                 err = bind(udev_monitor->sock,
 390                            &udev_monitor->snl.sa, sizeof(struct sockaddr_nl));
 391                 if (err == 0)
 392                         udev_monitor->bound = true;
 393         }
 394
 395         if (err >= 0)
 396                 monitor_set_nl_address(udev_monitor);
 397         else
 398                 return log_debug_errno(errno, "bind failed: %m");
 399
 400         /* enable receiving of sender credentials */
 401         err = setsockopt(udev_monitor->sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
 402         if (err < 0)
 403                 log_debug_errno(errno, "setting SO_PASSCRED failed: %m");
 404
 405         return 0;
 406 }
 407
 408 /**
 409  * udev_monitor_set_receive_buffer_size:
 410  * @udev_monitor: the monitor which should receive events
 411  * @size: the size in bytes
 412  *
 413  * Set the size of the kernel socket buffer. This call needs the
 414  * appropriate privileges to succeed.
 415  *
 416  * Returns: 0 on success, otherwise -1 on error.
 417  */
 418 _public_ int udev_monitor_set_receive_buffer_size(struct udev_monitor *udev_monitor, int size)
 419 {
 420         if (udev_monitor == NULL)
 421                 return -EINVAL;
 422         if (setsockopt(udev_monitor->sock, SOL_SOCKET, SO_RCVBUFFORCE, &size, sizeof(size)) < 0)
 423                 return -errno;
 424
 425         return 0;
 426 }
 427
 428 int udev_monitor_disconnect(struct udev_monitor *udev_monitor)
 429 {
 430         int err;
 431
 432         err = close(udev_monitor->sock);
 433         udev_monitor->sock = -1;
 434         return err < 0 ? -errno : 0;
 435 }
 436
 437 /**
 438  * udev_monitor_ref:
 439  * @udev_monitor: udev monitor
 440  *
 441  * Take a reference of a udev monitor.
 442  *
 443  * Returns: the passed udev monitor
 444  **/
 445 _public_ struct udev_monitor *udev_monitor_ref(struct udev_monitor *udev_monitor)
 446 {
 447         if (udev_monitor == NULL)
 448                 return NULL;
 449         udev_monitor->refcount++;
 450         return udev_monitor;
 451 }
 452
 453 /**
 454  * udev_monitor_unref:
 455  * @udev_monitor: udev monitor
 456  *
 457  * Drop a reference of a udev monitor. If the refcount reaches zero,
 458  * the bound socket will be closed, and the resources of the monitor
 459  * will be released.
 460  *
 461  * Returns: #NULL
 462  **/
 463 _public_ struct udev_monitor *udev_monitor_unref(struct udev_monitor *udev_monitor)
 464 {
 465         if (udev_monitor == NULL)
 466                 return NULL;
 467         udev_monitor->refcount--;
 468         if (udev_monitor->refcount > 0)
 469                 return NULL;
 470         if (udev_monitor->sock >= 0)
 471                 close(udev_monitor->sock);
 472         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
 473         udev_list_cleanup(&udev_monitor->filter_tag_list);
 474         return mfree(udev_monitor);
 475 }
 476
 477 /**
 478  * udev_monitor_get_udev:
 479  * @udev_monitor: udev monitor
 480  *
 481  * Retrieve the udev library context the monitor was created with.
 482  *
 483  * Returns: the udev library context
 484  **/
 485 _public_ struct udev *udev_monitor_get_udev(struct udev_monitor *udev_monitor)
 486 {
 487         if (udev_monitor == NULL)
 488                 return NULL;
 489         return udev_monitor->udev;
 490 }
 491
 492 /**
 493  * udev_monitor_get_fd:
 494  * @udev_monitor: udev monitor
 495  *
 496  * Retrieve the socket file descriptor associated with the monitor.
 497  *
 498  * Returns: the socket file descriptor
 499  **/
 500 _public_ int udev_monitor_get_fd(struct udev_monitor *udev_monitor)
 501 {
 502         if (udev_monitor == NULL)
 503                 return -EINVAL;
 504         return udev_monitor->sock;
 505 }
 506
 507 static int passes_filter(struct udev_monitor *udev_monitor, struct udev_device *udev_device)
 508 {
 509         struct udev_list_entry *list_entry;
 510
 511         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL)
 512                 goto tag;
 513         udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
 514                 const char *subsys = udev_list_entry_get_name(list_entry);
 515                 const char *dsubsys = udev_device_get_subsystem(udev_device);
 516                 const char *devtype;
 517                 const char *ddevtype;
 518
 519                 if (!streq(dsubsys, subsys))
 520                         continue;
 521
 522                 devtype = udev_list_entry_get_value(list_entry);
 523                 if (devtype == NULL)
 524                         goto tag;
 525                 ddevtype = udev_device_get_devtype(udev_device);
 526                 if (ddevtype == NULL)
 527                         continue;
 528                 if (streq(ddevtype, devtype))
 529                         goto tag;
 530         }
 531         return 0;
 532
 533 tag:
 534         if (udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
 535                 return 1;
 536         udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
 537                 const char *tag = udev_list_entry_get_name(list_entry);
 538
 539                 if (udev_device_has_tag(udev_device, tag))
 540                         return 1;
 541         }
 542         return 0;
 543 }
 544
 545 /**
 546  * udev_monitor_receive_device:
 547  * @udev_monitor: udev monitor
 548  *
 549  * Receive data from the udev monitor socket, allocate a new udev
 550  * device, fill in the received data, and return the device.
 551  *
 552  * Only socket connections with uid=0 are accepted.
 553  *
 554  * The monitor socket is by default set to NONBLOCK. A variant of poll() on
 555  * the file descriptor returned by udev_monitor_get_fd() should to be used to
 556  * wake up when new devices arrive, or alternatively the file descriptor
 557  * switched into blocking mode.
 558  *
 559  * The initial refcount is 1, and needs to be decremented to
 560  * release the resources of the udev device.
 561  *
 562  * Returns: a new udev device, or #NULL, in case of an error
 563  **/
 564 _public_ struct udev_device *udev_monitor_receive_device(struct udev_monitor *udev_monitor)
 565 {
 566         struct udev_device *udev_device;
 567         struct msghdr smsg;
 568         struct iovec iov;
 569         char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
 570         struct cmsghdr *cmsg;
 571         union sockaddr_union snl;
 572         struct ucred *cred;
 573         union {
 574                 struct udev_monitor_netlink_header nlh;
 575                 char raw[8192];
 576         } buf;
 577         ssize_t buflen;
 578         ssize_t bufpos;
 579         bool is_initialized = false;
 580
 581 retry:
 582         if (udev_monitor == NULL) {
 583                 errno = EINVAL;
 584                 return NULL;
 585         }
 586         iov.iov_base = &buf;
 587         iov.iov_len = sizeof(buf);
 588         memzero(&smsg, sizeof(struct msghdr));
 589         smsg.msg_iov = &iov;
 590         smsg.msg_iovlen = 1;
 591         smsg.msg_control = cred_msg;
 592         smsg.msg_controllen = sizeof(cred_msg);
 593         smsg.msg_name = &snl;
 594         smsg.msg_namelen = sizeof(snl);
 595
 596         buflen = recvmsg(udev_monitor->sock, &smsg, 0);
 597         if (buflen < 0) {
 598                 if (errno != EINTR)
 599                         log_debug("unable to receive message");
 600                 return NULL;
 601         }
 602
 603         if (buflen < 32 || (smsg.msg_flags & MSG_TRUNC)) {
 604                 log_debug("invalid message length");
 605                 errno = EINVAL;
 606                 return NULL;
 607         }
 608
 609         if (snl.nl.nl_groups == 0) {
 610                 /* unicast message, check if we trust the sender */
 611                 if (udev_monitor->snl_trusted_sender.nl.nl_pid == 0 ||
 612                     snl.nl.nl_pid != udev_monitor->snl_trusted_sender.nl.nl_pid) {
 613                         log_debug("unicast netlink message ignored");
 614                         errno = EAGAIN;
 615                         return NULL;
 616                 }
 617         } else if (snl.nl.nl_groups == UDEV_MONITOR_KERNEL) {
 618                 if (snl.nl.nl_pid > 0) {
 619                         log_debug("multicast kernel netlink message from PID %"PRIu32" ignored",
 620                                   snl.nl.nl_pid);
 621                         errno = EAGAIN;
 622                         return NULL;
 623                 }
 624         }
 625
 626         cmsg = CMSG_FIRSTHDR(&smsg);
 627         if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
 628                 log_debug("no sender credentials received, message ignored");
 629                 errno = EAGAIN;
 630                 return NULL;
 631         }
 632
 633         cred = (struct ucred *)CMSG_DATA(cmsg);
 634         if (cred->uid != 0) {
 635                 log_debug("sender uid="UID_FMT", message ignored", cred->uid);
 636                 errno = EAGAIN;
 637                 return NULL;
 638         }
 639
 640         if (memcmp(buf.raw, "libudev", 8) == 0) {
 641                 /* udev message needs proper version magic */
 642                 if (buf.nlh.magic != htobe32(UDEV_MONITOR_MAGIC)) {
 643                         log_debug("unrecognized message signature (%x != %x)",
 644                                  buf.nlh.magic, htobe32(UDEV_MONITOR_MAGIC));
 645                         errno = EAGAIN;
 646                         return NULL;
 647                 }
 648                 if (buf.nlh.properties_off+32 > (size_t)buflen) {
 649                         log_debug("message smaller than expected (%u > %zd)",
 650                                   buf.nlh.properties_off+32, buflen);
 651                         errno = EAGAIN;
 652                         return NULL;
 653                 }
 654
 655                 bufpos = buf.nlh.properties_off;
 656
 657                 /* devices received from udev are always initialized */
 658                 is_initialized = true;
 659         } else {
 660                 /* kernel message with header */
 661                 bufpos = strlen(buf.raw) + 1;
 662                 if ((size_t)bufpos < sizeof("a@/d") || bufpos >= buflen) {
 663                         log_debug("invalid message length");
 664                         errno = EAGAIN;
 665                         return NULL;
 666                 }
 667
 668                 /* check message header */
 669                 if (strstr(buf.raw, "@/") == NULL) {
 670                         log_debug("unrecognized message header");
 671                         errno = EAGAIN;
 672                         return NULL;
 673                 }
 674         }
 675
 676         udev_device = udev_device_new_from_nulstr(udev_monitor->udev, &buf.raw[bufpos], buflen - bufpos);
 677         if (!udev_device) {
 678                 log_debug_errno(errno, "could not create device: %m");
 679                 return NULL;
 680         }
 681
 682         if (is_initialized)
 683                 udev_device_set_is_initialized(udev_device);
 684
 685         /* skip device, if it does not pass the current filter */
 686         if (!passes_filter(udev_monitor, udev_device)) {
 687                 struct pollfd pfd[1];
 688                 int rc;
 689
 690                 udev_device_unref(udev_device);
 691
 692                 /* if something is queued, get next device */
 693                 pfd[0].fd = udev_monitor->sock;
 694                 pfd[0].events = POLLIN;
 695                 rc = poll(pfd, 1, 0);
 696                 if (rc > 0)
 697                         goto retry;
 698
 699                 errno = EAGAIN;
 700                 return NULL;
 701         }
 702
 703         return udev_device;
 704 }
 705
 706 int udev_monitor_receive_sd_device(struct udev_monitor *udev_monitor, sd_device **ret) {
 707         _cleanup_(udev_device_unrefp) struct udev_device *udev_device = NULL;
 708
 709         assert(ret);
 710
 711         udev_device = udev_monitor_receive_device(udev_monitor);
 712         if (!udev_device)
 713                 return -errno;
 714
 715         *ret = sd_device_ref(udev_device->device);
 716         return 0;
 717 }
 718
 719 int udev_monitor_send_device(struct udev_monitor *udev_monitor,
 720                              struct udev_monitor *destination, struct udev_device *udev_device)
 721 {
 722         const char *buf, *val;
 723         ssize_t blen, count;
 724         struct udev_monitor_netlink_header nlh = {
 725                 .prefix = "libudev",
 726                 .magic = htobe32(UDEV_MONITOR_MAGIC),
 727                 .header_size = sizeof nlh,
 728         };
 729         struct iovec iov[2] = {
 730                 { .iov_base = &nlh, .iov_len = sizeof nlh },
 731         };
 732         struct msghdr smsg = {
 733                 .msg_iov = iov,
 734                 .msg_iovlen = 2,
 735         };
 736         struct udev_list_entry *list_entry;
 737         uint64_t tag_bloom_bits;
 738
 739         blen = udev_device_get_properties_monitor_buf(udev_device, &buf);
 740         if (blen < 32) {
 741                 log_debug("device buffer is too small to contain a valid device");
 742                 return -EINVAL;
 743         }
 744
 745         /* fill in versioned header */
 746         val = udev_device_get_subsystem(udev_device);
 747         nlh.filter_subsystem_hash = htobe32(util_string_hash32(val));
 748
 749         val = udev_device_get_devtype(udev_device);
 750         if (val != NULL)
 751                 nlh.filter_devtype_hash = htobe32(util_string_hash32(val));
 752
 753         /* add tag bloom filter */
 754         tag_bloom_bits = 0;
 755         udev_list_entry_foreach(list_entry, udev_device_get_tags_list_entry(udev_device))
 756                 tag_bloom_bits |= util_string_bloom64(udev_list_entry_get_name(list_entry));
 757         if (tag_bloom_bits > 0) {
 758                 nlh.filter_tag_bloom_hi = htobe32(tag_bloom_bits >> 32);
 759                 nlh.filter_tag_bloom_lo = htobe32(tag_bloom_bits & 0xffffffff);
 760         }
 761
 762         /* add properties list */
 763         nlh.properties_off = iov[0].iov_len;
 764         nlh.properties_len = blen;
 765         iov[1].iov_base = (char *)buf;
 766         iov[1].iov_len = blen;
 767
 768         /*
 769          * Use custom address for target, or the default one.
 770          *
 771          * If we send to a multicast group, we will get
 772          * ECONNREFUSED, which is expected.
 773          */
 774         if (destination)
 775                 smsg.msg_name = &destination->snl;
 776         else
 777                 smsg.msg_name = &udev_monitor->snl_destination;
 778         smsg.msg_namelen = sizeof(struct sockaddr_nl);
 779         count = sendmsg(udev_monitor->sock, &smsg, 0);
 780         if (count < 0) {
 781                 if (!destination && errno == ECONNREFUSED) {
 782                         log_debug("passed device to netlink monitor %p", udev_monitor);
 783                         return 0;
 784                 } else
 785                         return -errno;
 786         }
 787
 788         log_debug("passed %zi byte device to netlink monitor %p", count, udev_monitor);
 789         return count;
 790 }
 791
 792 /**
 793  * udev_monitor_filter_add_match_subsystem_devtype:
 794  * @udev_monitor: the monitor
 795  * @subsystem: the subsystem value to match the incoming devices against
 796  * @devtype: the devtype value to match the incoming devices against
 797  *
 798  * This filter is efficiently executed inside the kernel, and libudev subscribers
 799  * will usually not be woken up for devices which do not match.
 800  *
 801  * The filter must be installed before the monitor is switched to listening mode.
 802  *
 803  * Returns: 0 on success, otherwise a negative error value.
 804  */
 805 _public_ int udev_monitor_filter_add_match_subsystem_devtype(struct udev_monitor *udev_monitor, const char *subsystem, const char *devtype)
 806 {
 807         if (udev_monitor == NULL)
 808                 return -EINVAL;
 809         if (subsystem == NULL)
 810                 return -EINVAL;
 811         if (udev_list_entry_add(&udev_monitor->filter_subsystem_list, subsystem, devtype) == NULL)
 812                 return -ENOMEM;
 813         return 0;
 814 }
 815
 816 /**
 817  * udev_monitor_filter_add_match_tag:
 818  * @udev_monitor: the monitor
 819  * @tag: the name of a tag
 820  *
 821  * This filter is efficiently executed inside the kernel, and libudev subscribers
 822  * will usually not be woken up for devices which do not match.
 823  *
 824  * The filter must be installed before the monitor is switched to listening mode.
 825  *
 826  * Returns: 0 on success, otherwise a negative error value.
 827  */
 828 _public_ int udev_monitor_filter_add_match_tag(struct udev_monitor *udev_monitor, const char *tag)
 829 {
 830         if (udev_monitor == NULL)
 831                 return -EINVAL;
 832         if (tag == NULL)
 833                 return -EINVAL;
 834         if (udev_list_entry_add(&udev_monitor->filter_tag_list, tag, NULL) == NULL)
 835                 return -ENOMEM;
 836         return 0;
 837 }
 838
 839 /**
 840  * udev_monitor_filter_remove:
 841  * @udev_monitor: monitor
 842  *
 843  * Remove all filters from monitor.
 844  *
 845  * Returns: 0 on success, otherwise a negative error value.
 846  */
 847 _public_ int udev_monitor_filter_remove(struct udev_monitor *udev_monitor)
 848 {
 849         static const struct sock_fprog filter = { 0, NULL };
 850
 851         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
 852         if (setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter)) < 0)
 853                 return -errno;
 854
 855         return 0;
 856 }