src/libudev/libudev-monitor.c

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