src/libudev/libudev-monitor.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   This file is part of systemd.
   4
   5   Copyright 2008-2012 Kay Sievers <kay@vrfy.org>
   6 ***/
   7
   8 #include <errno.h>
   9 #include <linux/filter.h>
  10 #include <linux/netlink.h>
  11 #include <poll.h>
  12 #include <stddef.h>
  13 #include <stdio.h>
  14 #include <stdlib.h>
  15 #include <string.h>
  16 #include <sys/socket.h>
  17 #include <unistd.h>
  18
  19 #include "libudev.h"
  20
  21 #include "alloc-util.h"
  22 #include "fd-util.h"
  23 #include "fileio.h"
  24 #include "format-util.h"
  25 #include "libudev-private.h"
  26 #include "missing.h"
  27 #include "mount-util.h"
  28 #include "socket-util.h"
  29 #include "string-util.h"
  30
  31 /**
  32  * SECTION:libudev-monitor
  33  * @short_description: device event source
  34  *
  35  * Connects to a device event source.
  36  */
  37
  38 /**
  39  * udev_monitor:
  40  *
  41  * Opaque object handling an event source.
  42  */
  43 struct udev_monitor {
  44         struct udev *udev;
  45         int refcount;
  46         int sock;
  47         union sockaddr_union snl;
  48         union sockaddr_union snl_trusted_sender;
  49         union sockaddr_union snl_destination;
  50         socklen_t addrlen;
  51         struct udev_list filter_subsystem_list;
  52         struct udev_list filter_tag_list;
  53         bool bound;
  54 };
  55
  56 enum udev_monitor_netlink_group {
  57         UDEV_MONITOR_NONE,
  58         UDEV_MONITOR_KERNEL,
  59         UDEV_MONITOR_UDEV,
  60 };
  61
  62 #define UDEV_MONITOR_MAGIC                0xfeedcafe
  63 struct udev_monitor_netlink_header {
  64         /* "libudev" prefix to distinguish libudev and kernel messages */
  65         char prefix[8];
  66         /*
  67          * magic to protect against daemon <-> library message format mismatch
  68          * used in the kernel from socket filter rules; needs to be stored in network order
  69          */
  70         unsigned int magic;
  71         /* total length of header structure known to the sender */
  72         unsigned int header_size;
  73         /* properties string buffer */
  74         unsigned int properties_off;
  75         unsigned int properties_len;
  76         /*
  77          * hashes of primary device properties strings, to let libudev subscribers
  78          * use in-kernel socket filters; values need to be stored in network order
  79          */
  80         unsigned int filter_subsystem_hash;
  81         unsigned int filter_devtype_hash;
  82         unsigned int filter_tag_bloom_hi;
  83         unsigned int filter_tag_bloom_lo;
  84 };
  85
  86 static struct udev_monitor *udev_monitor_new(struct udev *udev) {
  87         struct udev_monitor *udev_monitor;
  88
  89         udev_monitor = new0(struct udev_monitor, 1);
  90         if (udev_monitor == NULL) {
  91                 errno = ENOMEM;
  92                 return NULL;
  93         }
  94         udev_monitor->refcount = 1;
  95         udev_monitor->udev = udev;
  96         udev_list_init(udev, &udev_monitor->filter_subsystem_list, false);
  97         udev_list_init(udev, &udev_monitor->filter_tag_list, true);
  98         return udev_monitor;
  99 }
 100
 101 /* we consider udev running when /dev is on devtmpfs */
 102 static bool udev_has_devtmpfs(struct udev *udev) {
 103
 104         _cleanup_fclose_ FILE *f = NULL;
 105         char line[LINE_MAX], *e;
 106         int mount_id, r;
 107
 108         r = path_get_mnt_id("/dev", &mount_id);
 109         if (r < 0) {
 110                 if (r != -EOPNOTSUPP)
 111                         log_debug_errno(r, "name_to_handle_at on /dev: %m");
 112
 113                 return false;
 114         }
 115
 116         f = fopen("/proc/self/mountinfo", "re");
 117         if (!f)
 118                 return false;
 119
 120         FOREACH_LINE(line, f, return false) {
 121                 int mid;
 122
 123                 if (sscanf(line, "%i", &mid) != 1)
 124                         continue;
 125
 126                 if (mid != mount_id)
 127                         continue;
 128
 129                 e = strstr(line, " - ");
 130                 if (!e)
 131                         continue;
 132
 133                 /* accept any name that starts with the currently expected type */
 134                 if (startswith(e + 3, "devtmpfs"))
 135                         return true;
 136         }
 137
 138         return false;
 139 }
 140
 141 static void monitor_set_nl_address(struct udev_monitor *udev_monitor) {
 142         union sockaddr_union snl;
 143         socklen_t addrlen;
 144         int r;
 145
 146         assert(udev_monitor);
 147
 148         /* get the address the kernel has assigned us
 149          * it is usually, but not necessarily the pid
 150          */
 151         addrlen = sizeof(struct sockaddr_nl);
 152         r = getsockname(udev_monitor->sock, &snl.sa, &addrlen);
 153         if (r >= 0)
 154                 udev_monitor->snl.nl.nl_pid = snl.nl.nl_pid;
 155 }
 156
 157 struct udev_monitor *udev_monitor_new_from_netlink_fd(struct udev *udev, const char *name, int fd) {
 158         struct udev_monitor *udev_monitor;
 159         unsigned int group;
 160
 161         if (udev == NULL) {
 162                 errno = EINVAL;
 163                 return NULL;
 164         }
 165
 166         if (name == NULL)
 167                 group = UDEV_MONITOR_NONE;
 168         else if (streq(name, "udev")) {
 169                 /*
 170                  * We do not support subscribing to uevents if no instance of
 171                  * udev is running. Uevents would otherwise broadcast the
 172                  * processing data of the host into containers, which is not
 173                  * desired.
 174                  *
 175                  * Containers will currently not get any udev uevents, until
 176                  * a supporting infrastructure is available.
 177                  *
 178                  * We do not set a netlink multicast group here, so the socket
 179                  * will not receive any messages.
 180                  */
 181                 if (access("/run/udev/control", F_OK) < 0 && !udev_has_devtmpfs(udev)) {
 182                         log_debug("the udev service seems not to be active, disable the monitor");
 183                         group = UDEV_MONITOR_NONE;
 184                 } else
 185                         group = UDEV_MONITOR_UDEV;
 186         } else if (streq(name, "kernel"))
 187                 group = UDEV_MONITOR_KERNEL;
 188         else {
 189                 errno = EINVAL;
 190                 return NULL;
 191         }
 192
 193         udev_monitor = udev_monitor_new(udev);
 194         if (udev_monitor == NULL)
 195                 return NULL;
 196
 197         if (fd < 0) {
 198                 udev_monitor->sock = socket(PF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_KOBJECT_UEVENT);
 199                 if (udev_monitor->sock < 0) {
 200                         log_debug_errno(errno, "error getting socket: %m");
 201                         return mfree(udev_monitor);
 202                 }
 203         } else {
 204                 udev_monitor->bound = true;
 205                 udev_monitor->sock = fd;
 206                 monitor_set_nl_address(udev_monitor);
 207         }
 208
 209         udev_monitor->snl.nl.nl_family = AF_NETLINK;
 210         udev_monitor->snl.nl.nl_groups = group;
 211
 212         /* default destination for sending */
 213         udev_monitor->snl_destination.nl.nl_family = AF_NETLINK;
 214         udev_monitor->snl_destination.nl.nl_groups = UDEV_MONITOR_UDEV;
 215
 216         return udev_monitor;
 217 }
 218
 219 /**
 220  * udev_monitor_new_from_netlink:
 221  * @udev: udev library context
 222  * @name: name of event source
 223  *
 224  * Create new udev monitor and connect to a specified event
 225  * source. Valid sources identifiers are "udev" and "kernel".
 226  *
 227  * Applications should usually not connect directly to the
 228  * "kernel" events, because the devices might not be useable
 229  * at that time, before udev has configured them, and created
 230  * device nodes. Accessing devices at the same time as udev,
 231  * might result in unpredictable behavior. The "udev" events
 232  * are sent out after udev has finished its event processing,
 233  * all rules have been processed, and needed device nodes are
 234  * created.
 235  *
 236  * The initial refcount is 1, and needs to be decremented to
 237  * release the resources of the udev monitor.
 238  *
 239  * Returns: a new udev monitor, or #NULL, in case of an error
 240  **/
 241 _public_ struct udev_monitor *udev_monitor_new_from_netlink(struct udev *udev, const char *name) {
 242         return udev_monitor_new_from_netlink_fd(udev, name, -1);
 243 }
 244
 245 static inline void bpf_stmt(struct sock_filter *inss, unsigned int *i,
 246                             unsigned short code, unsigned int data)
 247 {
 248         struct sock_filter *ins = &inss[*i];
 249
 250         ins->code = code;
 251         ins->k = data;
 252         (*i)++;
 253 }
 254
 255 static inline void bpf_jmp(struct sock_filter *inss, unsigned int *i,
 256                            unsigned short code, unsigned int data,
 257                            unsigned short jt, unsigned short jf)
 258 {
 259         struct sock_filter *ins = &inss[*i];
 260
 261         ins->code = code;
 262         ins->jt = jt;
 263         ins->jf = jf;
 264         ins->k = data;
 265         (*i)++;
 266 }
 267
 268 /**
 269  * udev_monitor_filter_update:
 270  * @udev_monitor: monitor
 271  *
 272  * Update the installed socket filter. This is only needed,
 273  * if the filter was removed or changed.
 274  *
 275  * Returns: 0 on success, otherwise a negative error value.
 276  */
 277 _public_ int udev_monitor_filter_update(struct udev_monitor *udev_monitor)
 278 {
 279         struct sock_filter ins[512];
 280         struct sock_fprog filter;
 281         unsigned int i;
 282         struct udev_list_entry *list_entry;
 283         int err;
 284
 285         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL &&
 286             udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
 287                 return 0;
 288
 289         memzero(ins, sizeof(ins));
 290         i = 0;
 291
 292         /* load magic in A */
 293         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, magic));
 294         /* jump if magic matches */
 295         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, UDEV_MONITOR_MAGIC, 1, 0);
 296         /* wrong magic, pass packet */
 297         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 298
 299         if (udev_list_get_entry(&udev_monitor->filter_tag_list) != NULL) {
 300                 int tag_matches;
 301
 302                 /* count tag matches, to calculate end of tag match block */
 303                 tag_matches = 0;
 304                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list))
 305                         tag_matches++;
 306
 307                 /* add all tags matches */
 308                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
 309                         uint64_t tag_bloom_bits = util_string_bloom64(udev_list_entry_get_name(list_entry));
 310                         uint32_t tag_bloom_hi = tag_bloom_bits >> 32;
 311                         uint32_t tag_bloom_lo = tag_bloom_bits & 0xffffffff;
 312
 313                         /* load device bloom bits in A */
 314                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_hi));
 315                         /* clear bits (tag bits & bloom bits) */
 316                         bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_hi);
 317                         /* jump to next tag if it does not match */
 318                         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_hi, 0, 3);
 319
 320                         /* load device bloom bits in A */
 321                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_tag_bloom_lo));
 322                         /* clear bits (tag bits & bloom bits) */
 323                         bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_lo);
 324                         /* jump behind end of tag match block if tag matches */
 325                         tag_matches--;
 326                         bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_lo, 1 + (tag_matches * 6), 0);
 327                 }
 328
 329                 /* nothing matched, drop packet */
 330                 bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
 331         }
 332
 333         /* add all subsystem matches */
 334         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) != NULL) {
 335                 udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
 336                         unsigned int hash = util_string_hash32(udev_list_entry_get_name(list_entry));
 337
 338                         /* load device subsystem value in A */
 339                         bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_subsystem_hash));
 340                         if (udev_list_entry_get_value(list_entry) == NULL) {
 341                                 /* jump if subsystem does not match */
 342                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
 343                         } else {
 344                                 /* jump if subsystem does not match */
 345                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 3);
 346
 347                                 /* load device devtype value in A */
 348                                 bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(struct udev_monitor_netlink_header, filter_devtype_hash));
 349                                 /* jump if value does not match */
 350                                 hash = util_string_hash32(udev_list_entry_get_value(list_entry));
 351                                 bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
 352                         }
 353
 354                         /* matched, pass packet */
 355                         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 356
 357                         if (i+1 >= ELEMENTSOF(ins))
 358                                 return -E2BIG;
 359                 }
 360
 361                 /* nothing matched, drop packet */
 362                 bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
 363         }
 364
 365         /* matched, pass packet */
 366         bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
 367
 368         /* install filter */
 369         memzero(&filter, sizeof(filter));
 370         filter.len = i;
 371         filter.filter = ins;
 372         err = setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter));
 373         return err < 0 ? -errno : 0;
 374 }
 375
 376 int udev_monitor_allow_unicast_sender(struct udev_monitor *udev_monitor, struct udev_monitor *sender)
 377 {
 378         udev_monitor->snl_trusted_sender.nl.nl_pid = sender->snl.nl.nl_pid;
 379         return 0;
 380 }
 381
 382 /**
 383  * udev_monitor_enable_receiving:
 384  * @udev_monitor: the monitor which should receive events
 385  *
 386  * Binds the @udev_monitor socket to the event source.
 387  *
 388  * Returns: 0 on success, otherwise a negative error value.
 389  */
 390 _public_ int udev_monitor_enable_receiving(struct udev_monitor *udev_monitor)
 391 {
 392         int err = 0;
 393         const int on = 1;
 394
 395         udev_monitor_filter_update(udev_monitor);
 396
 397         if (!udev_monitor->bound) {
 398                 err = bind(udev_monitor->sock,
 399                            &udev_monitor->snl.sa, sizeof(struct sockaddr_nl));
 400                 if (err == 0)
 401                         udev_monitor->bound = true;
 402         }
 403
 404         if (err >= 0)
 405                 monitor_set_nl_address(udev_monitor);
 406         else
 407                 return log_debug_errno(errno, "bind failed: %m");
 408
 409         /* enable receiving of sender credentials */
 410         err = setsockopt(udev_monitor->sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
 411         if (err < 0)
 412                 log_debug_errno(errno, "setting SO_PASSCRED failed: %m");
 413
 414         return 0;
 415 }
 416
 417 /**
 418  * udev_monitor_set_receive_buffer_size:
 419  * @udev_monitor: the monitor which should receive events
 420  * @size: the size in bytes
 421  *
 422  * Set the size of the kernel socket buffer. This call needs the
 423  * appropriate privileges to succeed.
 424  *
 425  * Returns: 0 on success, otherwise -1 on error.
 426  */
 427 _public_ int udev_monitor_set_receive_buffer_size(struct udev_monitor *udev_monitor, int size)
 428 {
 429         if (udev_monitor == NULL)
 430                 return -EINVAL;
 431         if (setsockopt(udev_monitor->sock, SOL_SOCKET, SO_RCVBUFFORCE, &size, sizeof(size)) < 0)
 432                 return -errno;
 433
 434         return 0;
 435 }
 436
 437 int udev_monitor_disconnect(struct udev_monitor *udev_monitor)
 438 {
 439         int err;
 440
 441         err = close(udev_monitor->sock);
 442         udev_monitor->sock = -1;
 443         return err < 0 ? -errno : 0;
 444 }
 445
 446 /**
 447  * udev_monitor_ref:
 448  * @udev_monitor: udev monitor
 449  *
 450  * Take a reference of a udev monitor.
 451  *
 452  * Returns: the passed udev monitor
 453  **/
 454 _public_ struct udev_monitor *udev_monitor_ref(struct udev_monitor *udev_monitor)
 455 {
 456         if (udev_monitor == NULL)
 457                 return NULL;
 458         udev_monitor->refcount++;
 459         return udev_monitor;
 460 }
 461
 462 /**
 463  * udev_monitor_unref:
 464  * @udev_monitor: udev monitor
 465  *
 466  * Drop a reference of a udev monitor. If the refcount reaches zero,
 467  * the bound socket will be closed, and the resources of the monitor
 468  * will be released.
 469  *
 470  * Returns: #NULL
 471  **/
 472 _public_ struct udev_monitor *udev_monitor_unref(struct udev_monitor *udev_monitor)
 473 {
 474         if (udev_monitor == NULL)
 475                 return NULL;
 476         udev_monitor->refcount--;
 477         if (udev_monitor->refcount > 0)
 478                 return NULL;
 479         if (udev_monitor->sock >= 0)
 480                 close(udev_monitor->sock);
 481         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
 482         udev_list_cleanup(&udev_monitor->filter_tag_list);
 483         return mfree(udev_monitor);
 484 }
 485
 486 /**
 487  * udev_monitor_get_udev:
 488  * @udev_monitor: udev monitor
 489  *
 490  * Retrieve the udev library context the monitor was created with.
 491  *
 492  * Returns: the udev library context
 493  **/
 494 _public_ struct udev *udev_monitor_get_udev(struct udev_monitor *udev_monitor)
 495 {
 496         if (udev_monitor == NULL)
 497                 return NULL;
 498         return udev_monitor->udev;
 499 }
 500
 501 /**
 502  * udev_monitor_get_fd:
 503  * @udev_monitor: udev monitor
 504  *
 505  * Retrieve the socket file descriptor associated with the monitor.
 506  *
 507  * Returns: the socket file descriptor
 508  **/
 509 _public_ int udev_monitor_get_fd(struct udev_monitor *udev_monitor)
 510 {
 511         if (udev_monitor == NULL)
 512                 return -EINVAL;
 513         return udev_monitor->sock;
 514 }
 515
 516 static int passes_filter(struct udev_monitor *udev_monitor, struct udev_device *udev_device)
 517 {
 518         struct udev_list_entry *list_entry;
 519
 520         if (udev_list_get_entry(&udev_monitor->filter_subsystem_list) == NULL)
 521                 goto tag;
 522         udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_subsystem_list)) {
 523                 const char *subsys = udev_list_entry_get_name(list_entry);
 524                 const char *dsubsys = udev_device_get_subsystem(udev_device);
 525                 const char *devtype;
 526                 const char *ddevtype;
 527
 528                 if (!streq(dsubsys, subsys))
 529                         continue;
 530
 531                 devtype = udev_list_entry_get_value(list_entry);
 532                 if (devtype == NULL)
 533                         goto tag;
 534                 ddevtype = udev_device_get_devtype(udev_device);
 535                 if (ddevtype == NULL)
 536                         continue;
 537                 if (streq(ddevtype, devtype))
 538                         goto tag;
 539         }
 540         return 0;
 541
 542 tag:
 543         if (udev_list_get_entry(&udev_monitor->filter_tag_list) == NULL)
 544                 return 1;
 545         udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_monitor->filter_tag_list)) {
 546                 const char *tag = udev_list_entry_get_name(list_entry);
 547
 548                 if (udev_device_has_tag(udev_device, tag))
 549                         return 1;
 550         }
 551         return 0;
 552 }
 553
 554 /**
 555  * udev_monitor_receive_device:
 556  * @udev_monitor: udev monitor
 557  *
 558  * Receive data from the udev monitor socket, allocate a new udev
 559  * device, fill in the received data, and return the device.
 560  *
 561  * Only socket connections with uid=0 are accepted.
 562  *
 563  * The monitor socket is by default set to NONBLOCK. A variant of poll() on
 564  * the file descriptor returned by udev_monitor_get_fd() should to be used to
 565  * wake up when new devices arrive, or alternatively the file descriptor
 566  * switched into blocking mode.
 567  *
 568  * The initial refcount is 1, and needs to be decremented to
 569  * release the resources of the udev device.
 570  *
 571  * Returns: a new udev device, or #NULL, in case of an error
 572  **/
 573 _public_ struct udev_device *udev_monitor_receive_device(struct udev_monitor *udev_monitor)
 574 {
 575         struct udev_device *udev_device;
 576         struct msghdr smsg;
 577         struct iovec iov;
 578         char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
 579         struct cmsghdr *cmsg;
 580         union sockaddr_union snl;
 581         struct ucred *cred;
 582         union {
 583                 struct udev_monitor_netlink_header nlh;
 584                 char raw[8192];
 585         } buf;
 586         ssize_t buflen;
 587         ssize_t bufpos;
 588         bool is_initialized = false;
 589
 590 retry:
 591         if (udev_monitor == NULL) {
 592                 errno = EINVAL;
 593                 return NULL;
 594         }
 595         iov.iov_base = &buf;
 596         iov.iov_len = sizeof(buf);
 597         memzero(&smsg, sizeof(struct msghdr));
 598         smsg.msg_iov = &iov;
 599         smsg.msg_iovlen = 1;
 600         smsg.msg_control = cred_msg;
 601         smsg.msg_controllen = sizeof(cred_msg);
 602         smsg.msg_name = &snl;
 603         smsg.msg_namelen = sizeof(snl);
 604
 605         buflen = recvmsg(udev_monitor->sock, &smsg, 0);
 606         if (buflen < 0) {
 607                 if (errno != EINTR)
 608                         log_debug("unable to receive message");
 609                 return NULL;
 610         }
 611
 612         if (buflen < 32 || (smsg.msg_flags & MSG_TRUNC)) {
 613                 log_debug("invalid message length");
 614                 errno = EINVAL;
 615                 return NULL;
 616         }
 617
 618         if (snl.nl.nl_groups == 0) {
 619                 /* unicast message, check if we trust the sender */
 620                 if (udev_monitor->snl_trusted_sender.nl.nl_pid == 0 ||
 621                     snl.nl.nl_pid != udev_monitor->snl_trusted_sender.nl.nl_pid) {
 622                         log_debug("unicast netlink message ignored");
 623                         errno = EAGAIN;
 624                         return NULL;
 625                 }
 626         } else if (snl.nl.nl_groups == UDEV_MONITOR_KERNEL) {
 627                 if (snl.nl.nl_pid > 0) {
 628                         log_debug("multicast kernel netlink message from PID %"PRIu32" ignored",
 629                                   snl.nl.nl_pid);
 630                         errno = EAGAIN;
 631                         return NULL;
 632                 }
 633         }
 634
 635         cmsg = CMSG_FIRSTHDR(&smsg);
 636         if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
 637                 log_debug("no sender credentials received, message ignored");
 638                 errno = EAGAIN;
 639                 return NULL;
 640         }
 641
 642         cred = (struct ucred *)CMSG_DATA(cmsg);
 643         if (cred->uid != 0) {
 644                 log_debug("sender uid="UID_FMT", message ignored", cred->uid);
 645                 errno = EAGAIN;
 646                 return NULL;
 647         }
 648
 649         if (memcmp(buf.raw, "libudev", 8) == 0) {
 650                 /* udev message needs proper version magic */
 651                 if (buf.nlh.magic != htobe32(UDEV_MONITOR_MAGIC)) {
 652                         log_debug("unrecognized message signature (%x != %x)",
 653                                  buf.nlh.magic, htobe32(UDEV_MONITOR_MAGIC));
 654                         errno = EAGAIN;
 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                         errno = EAGAIN;
 661                         return NULL;
 662                 }
 663
 664                 bufpos = buf.nlh.properties_off;
 665
 666                 /* devices received from udev are always initialized */
 667                 is_initialized = true;
 668         } else {
 669                 /* kernel message with header */
 670                 bufpos = strlen(buf.raw) + 1;
 671                 if ((size_t)bufpos < sizeof("a@/d") || bufpos >= buflen) {
 672                         log_debug("invalid message length");
 673                         errno = EAGAIN;
 674                         return NULL;
 675                 }
 676
 677                 /* check message header */
 678                 if (strstr(buf.raw, "@/") == NULL) {
 679                         log_debug("unrecognized message header");
 680                         errno = EAGAIN;
 681                         return NULL;
 682                 }
 683         }
 684
 685         udev_device = udev_device_new_from_nulstr(udev_monitor->udev, &buf.raw[bufpos], buflen - bufpos);
 686         if (!udev_device) {
 687                 log_debug_errno(errno, "could not create device: %m");
 688                 return NULL;
 689         }
 690
 691         if (is_initialized)
 692                 udev_device_set_is_initialized(udev_device);
 693
 694         /* skip device, if it does not pass the current filter */
 695         if (!passes_filter(udev_monitor, udev_device)) {
 696                 struct pollfd pfd[1];
 697                 int rc;
 698
 699                 udev_device_unref(udev_device);
 700
 701                 /* if something is queued, get next device */
 702                 pfd[0].fd = udev_monitor->sock;
 703                 pfd[0].events = POLLIN;
 704                 rc = poll(pfd, 1, 0);
 705                 if (rc > 0)
 706                         goto retry;
 707
 708                 errno = EAGAIN;
 709                 return NULL;
 710         }
 711
 712         return udev_device;
 713 }
 714
 715 int udev_monitor_send_device(struct udev_monitor *udev_monitor,
 716                              struct udev_monitor *destination, struct udev_device *udev_device)
 717 {
 718         const char *buf, *val;
 719         ssize_t blen, count;
 720         struct udev_monitor_netlink_header nlh = {
 721                 .prefix = "libudev",
 722                 .magic = htobe32(UDEV_MONITOR_MAGIC),
 723                 .header_size = sizeof nlh,
 724         };
 725         struct iovec iov[2] = {
 726                 { .iov_base = &nlh, .iov_len = sizeof nlh },
 727         };
 728         struct msghdr smsg = {
 729                 .msg_iov = iov,
 730                 .msg_iovlen = 2,
 731         };
 732         struct udev_list_entry *list_entry;
 733         uint64_t tag_bloom_bits;
 734
 735         blen = udev_device_get_properties_monitor_buf(udev_device, &buf);
 736         if (blen < 32) {
 737                 log_debug("device buffer is too small to contain a valid device");
 738                 return -EINVAL;
 739         }
 740
 741         /* fill in versioned header */
 742         val = udev_device_get_subsystem(udev_device);
 743         nlh.filter_subsystem_hash = htobe32(util_string_hash32(val));
 744
 745         val = udev_device_get_devtype(udev_device);
 746         if (val != NULL)
 747                 nlh.filter_devtype_hash = htobe32(util_string_hash32(val));
 748
 749         /* add tag bloom filter */
 750         tag_bloom_bits = 0;
 751         udev_list_entry_foreach(list_entry, udev_device_get_tags_list_entry(udev_device))
 752                 tag_bloom_bits |= util_string_bloom64(udev_list_entry_get_name(list_entry));
 753         if (tag_bloom_bits > 0) {
 754                 nlh.filter_tag_bloom_hi = htobe32(tag_bloom_bits >> 32);
 755                 nlh.filter_tag_bloom_lo = htobe32(tag_bloom_bits & 0xffffffff);
 756         }
 757
 758         /* add properties list */
 759         nlh.properties_off = iov[0].iov_len;
 760         nlh.properties_len = blen;
 761         iov[1].iov_base = (char *)buf;
 762         iov[1].iov_len = blen;
 763
 764         /*
 765          * Use custom address for target, or the default one.
 766          *
 767          * If we send to a multicast group, we will get
 768          * ECONNREFUSED, which is expected.
 769          */
 770         if (destination)
 771                 smsg.msg_name = &destination->snl;
 772         else
 773                 smsg.msg_name = &udev_monitor->snl_destination;
 774         smsg.msg_namelen = sizeof(struct sockaddr_nl);
 775         count = sendmsg(udev_monitor->sock, &smsg, 0);
 776         if (count < 0) {
 777                 if (!destination && errno == ECONNREFUSED) {
 778                         log_debug("passed device to netlink monitor %p", udev_monitor);
 779                         return 0;
 780                 } else
 781                         return -errno;
 782         }
 783
 784         log_debug("passed %zi byte device to netlink monitor %p", count, udev_monitor);
 785         return count;
 786 }
 787
 788 /**
 789  * udev_monitor_filter_add_match_subsystem_devtype:
 790  * @udev_monitor: the monitor
 791  * @subsystem: the subsystem value to match the incoming devices against
 792  * @devtype: the devtype value to match the incoming devices against
 793  *
 794  * This filter is efficiently executed inside the kernel, and libudev subscribers
 795  * will usually not be woken up for devices which do not match.
 796  *
 797  * The filter must be installed before the monitor is switched to listening mode.
 798  *
 799  * Returns: 0 on success, otherwise a negative error value.
 800  */
 801 _public_ int udev_monitor_filter_add_match_subsystem_devtype(struct udev_monitor *udev_monitor, const char *subsystem, const char *devtype)
 802 {
 803         if (udev_monitor == NULL)
 804                 return -EINVAL;
 805         if (subsystem == NULL)
 806                 return -EINVAL;
 807         if (udev_list_entry_add(&udev_monitor->filter_subsystem_list, subsystem, devtype) == NULL)
 808                 return -ENOMEM;
 809         return 0;
 810 }
 811
 812 /**
 813  * udev_monitor_filter_add_match_tag:
 814  * @udev_monitor: the monitor
 815  * @tag: the name of a tag
 816  *
 817  * This filter is efficiently executed inside the kernel, and libudev subscribers
 818  * will usually not be woken up for devices which do not match.
 819  *
 820  * The filter must be installed before the monitor is switched to listening mode.
 821  *
 822  * Returns: 0 on success, otherwise a negative error value.
 823  */
 824 _public_ int udev_monitor_filter_add_match_tag(struct udev_monitor *udev_monitor, const char *tag)
 825 {
 826         if (udev_monitor == NULL)
 827                 return -EINVAL;
 828         if (tag == NULL)
 829                 return -EINVAL;
 830         if (udev_list_entry_add(&udev_monitor->filter_tag_list, tag, NULL) == NULL)
 831                 return -ENOMEM;
 832         return 0;
 833 }
 834
 835 /**
 836  * udev_monitor_filter_remove:
 837  * @udev_monitor: monitor
 838  *
 839  * Remove all filters from monitor.
 840  *
 841  * Returns: 0 on success, otherwise a negative error value.
 842  */
 843 _public_ int udev_monitor_filter_remove(struct udev_monitor *udev_monitor)
 844 {
 845         static const struct sock_fprog filter = { 0, NULL };
 846
 847         udev_list_cleanup(&udev_monitor->filter_subsystem_list);
 848         if (setsockopt(udev_monitor->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter)) < 0)
 849                 return -errno;
 850
 851         return 0;
 852 }