src/journal/journald-audit.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Copyright 2014 Lennart Poettering
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU Lesser General Public License as published by
  10   the Free Software Foundation; either version 2.1 of the License, or
  11   (at your option) any later version.
  12
  13   systemd is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   Lesser General Public License for more details.
  17
  18   You should have received a copy of the GNU Lesser General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include "missing.h"
  23 #include "journald-audit.h"
  24
  25 typedef struct MapField {
  26         const char *audit_field;
  27         const char *journal_field;
  28         int (*map)(const char *field, const char **p, struct iovec **iov, size_t *n_iov_allocated, unsigned *n_iov);
  29 } MapField;
  30
  31 static int map_simple_field(const char *field, const char **p, struct iovec **iov, size_t *n_iov_allocated, unsigned *n_iov) {
  32         _cleanup_free_ char *c = NULL;
  33         size_t l = 0, allocated = 0;
  34         const char *e;
  35
  36         assert(field);
  37         assert(p);
  38         assert(iov);
  39         assert(n_iov);
  40
  41         l = strlen(field);
  42         allocated = l + 1;
  43         c = malloc(allocated);
  44         if (!c)
  45                 return -ENOMEM;
  46
  47         memcpy(c, field, l);
  48         for (e = *p; *e != ' ' && *e != 0; e++) {
  49                 if (!GREEDY_REALLOC(c, allocated, l+2))
  50                         return -ENOMEM;
  51
  52                 c[l++] = *e;
  53         }
  54
  55         c[l] = 0;
  56
  57         if (!GREEDY_REALLOC(*iov, *n_iov_allocated, *n_iov + 1))
  58                 return -ENOMEM;
  59
  60         (*iov)[*n_iov].iov_base = c;
  61         (*iov)[*n_iov].iov_len = l;
  62         (*n_iov) ++;
  63
  64         *p = e;
  65         c = NULL;
  66
  67         return 1;
  68 }
  69
  70 static int map_string_field_internal(const char *field, const char **p, struct iovec **iov, size_t *n_iov_allocated, unsigned *n_iov, bool filter_printable) {
  71         _cleanup_free_ char *c = NULL;
  72         const char *s, *e;
  73         size_t l;
  74
  75         assert(field);
  76         assert(p);
  77         assert(iov);
  78         assert(n_iov);
  79
  80         /* The kernel formats string fields in one of two formats. */
  81
  82         if (**p == '"') {
  83                 /* Normal quoted syntax */
  84                 s = *p + 1;
  85                 e = strchr(s, '"');
  86                 if (!e)
  87                         return 0;
  88
  89                 l = strlen(field) + (e - s);
  90                 c = malloc(l+1);
  91                 if (!c)
  92                         return -ENOMEM;
  93
  94                 *((char*) mempcpy(stpcpy(c, field), s, e - s)) = 0;
  95
  96                 e += 1;
  97
  98         } else if (unhexchar(**p) >= 0) {
  99                 /* Hexadecimal escaping */
 100                 size_t allocated = 0;
 101
 102                 l = strlen(field);
 103                 allocated = l + 2;
 104                 c = malloc(allocated);
 105                 if (!c)
 106                         return -ENOMEM;
 107
 108                 memcpy(c, field, l);
 109                 for (e = *p; *e != ' ' && *e != 0; e += 2) {
 110                         int a, b;
 111                         uint8_t x;
 112
 113                         a = unhexchar(e[0]);
 114                         if (a < 0)
 115                                 return 0;
 116
 117                         b = unhexchar(e[1]);
 118                         if (b < 0)
 119                                 return 0;
 120
 121                         x = ((uint8_t) a << 4 | (uint8_t) b);
 122
 123                         if (filter_printable && x < (uint8_t) ' ')
 124                                 x = (uint8_t) ' ';
 125
 126                         if (!GREEDY_REALLOC(c, allocated, l+2))
 127                                 return -ENOMEM;
 128
 129                         c[l++] = (char) x;
 130                 }
 131
 132                 c[l] = 0;
 133         } else
 134                 return 0;
 135
 136         if (!GREEDY_REALLOC(*iov, *n_iov_allocated, *n_iov + 1))
 137                 return -ENOMEM;
 138
 139         (*iov)[*n_iov].iov_base = c;
 140         (*iov)[*n_iov].iov_len = l;
 141         (*n_iov) ++;
 142
 143         *p = e;
 144         c = NULL;
 145
 146         return 1;
 147 }
 148
 149 static int map_string_field(const char *field, const char **p, struct iovec **iov, size_t *n_iov_allocated, unsigned *n_iov) {
 150         return map_string_field_internal(field, p, iov, n_iov_allocated, n_iov, false);
 151 }
 152
 153 static int map_string_field_printable(const char *field, const char **p, struct iovec **iov, size_t *n_iov_allocated, unsigned *n_iov) {
 154         return map_string_field_internal(field, p, iov, n_iov_allocated, n_iov, true);
 155 }
 156
 157 static int map_generic_field(const char *prefix, const char **p, struct iovec **iov, size_t *n_iov_allocated, unsigned *n_iov) {
 158         const char *e, *f;
 159         char *c, *t;
 160         int r;
 161
 162         /* Implements fallback mappings for all fields we don't know */
 163
 164         for (e = *p; e < *p + 16; e++) {
 165
 166                 if (*e == 0 || *e == ' ')
 167                         return 0;
 168
 169                 if (*e == '=')
 170                         break;
 171
 172                 if (!((*e >= 'a' && *e <= 'z') ||
 173                       (*e >= 'A' && *e <= 'Z') ||
 174                       (*e >= '0' && *e <= '9') ||
 175                       (*e == '_')))
 176                         return 0;
 177         }
 178
 179         if (e <= *p || e >= *p + 16)
 180                 return 0;
 181
 182         c = alloca(strlen(prefix) + (e - *p) + 2);
 183
 184         t = stpcpy(c, prefix);
 185         for (f = *p; f < e; f++)
 186                 *(t++) = *f >= 'a' && *f <= 'z' ? ((*f - 'a') + 'A') : *f;
 187         strcpy(t, "=");
 188
 189         e ++;
 190
 191         r = map_simple_field(c, &e, iov, n_iov_allocated, n_iov);
 192         if (r < 0)
 193                 return r;
 194
 195         *p = e;
 196         return r;
 197 }
 198
 199 /* Kernel fields are those occuring in the audit string before
 200  * msg='. All of these fields are trusted, hence carry the "_" prefix.
 201  * We try to translate the fields we know into our native names. The
 202  * other's are generically mapped to _AUDIT_FIELD_XYZ= */
 203 static const MapField map_fields_kernel[] = {
 204
 205         /* First, we map certain well-known audit fields into native
 206          * well-known fields */
 207         { "pid=",       "_PID=",                   map_simple_field },
 208         { "ppid=",      "_PPID=",                  map_simple_field },
 209         { "uid=",       "_UID=",                   map_simple_field },
 210         { "euid=",      "_EUID=",                  map_simple_field },
 211         { "fsuid=",     "_FSUID=",                 map_simple_field },
 212         { "gid=",       "_GID=",                   map_simple_field },
 213         { "egid=",      "_EGID=",                  map_simple_field },
 214         { "fsgid=",     "_FSGID=",                 map_simple_field },
 215         { "tty=",       "_TTY=",                   map_simple_field },
 216         { "ses=",       "_AUDIT_SESSION=",         map_simple_field },
 217         { "auid=",      "_AUDIT_LOGINUID=",        map_simple_field },
 218         { "subj=",      "_SELINUX_CONTEXT=",       map_simple_field },
 219         { "comm=",      "_COMM=",                  map_string_field },
 220         { "exe=",       "_EXE=",                   map_string_field },
 221         { "proctitle=", "_CMDLINE=",               map_string_field_printable },
 222
 223         /* Some fields don't map to native well-known fields. However,
 224          * we know that they are string fields, hence let's undo
 225          * string field escaping for them, though we stick to the
 226          * generic field names. */
 227         { "path=",      "_AUDIT_FIELD_PATH=",      map_string_field },
 228         { "dev=",       "_AUDIT_FIELD_DEV=",       map_string_field },
 229         { "name=",      "_AUDIT_FIELD_NAME=",      map_string_field },
 230         {}
 231 };
 232
 233 /* Userspace fields are thos occuring in the audit string after
 234  * msg='. All of these fields are untrusted, hence carry no "_"
 235  * prefix. We map the fields we don't know to AUDIT_FIELD_XYZ= */
 236 static const MapField map_fields_userspace[] = {
 237         { "cwd=",       "AUDIT_FIELD_CWD=",  map_string_field },
 238         { "cmd=",       "AUDIT_FIELD_CMD=",  map_string_field },
 239         { "acct=",      "AUDIT_FIELD_ACCT=", map_string_field },
 240         { "exe=",       "AUDIT_FIELD_EXE=",  map_string_field },
 241         { "comm=",      "AUDIT_FIELD_COMM=", map_string_field },
 242         {}
 243 };
 244
 245 static int map_all_fields(
 246                 const char *p,
 247                 const MapField map_fields[],
 248                 const char *prefix,
 249                 bool handle_msg,
 250                 struct iovec **iov,
 251                 size_t *n_iov_allocated,
 252                 unsigned *n_iov) {
 253
 254         int r;
 255
 256         assert(p);
 257         assert(iov);
 258         assert(n_iov_allocated);
 259         assert(n_iov);
 260
 261         for (;;) {
 262                 bool mapped = false;
 263                 const MapField *m;
 264                 const char *v;
 265
 266                 p += strspn(p, WHITESPACE);
 267
 268                 if (*p == 0)
 269                         return 0;
 270
 271                 if (handle_msg) {
 272                         v = startswith(p, "msg='");
 273                         if (v) {
 274                                 const char *e;
 275                                 char *c;
 276
 277                                 /* Userspace message. It's enclosed in
 278                                    simple quotation marks, is not
 279                                    escaped, but the last field in the
 280                                    line, hence let's remove the
 281                                    quotation mark, and apply the
 282                                    userspace mapping instead of the
 283                                    kernel mapping. */
 284
 285                                 e = endswith(v, "'");
 286                                 if (!e)
 287                                         return 0; /* don't continue splitting up if the final quotation mark is missing */
 288
 289                                 c = strndupa(v, e - v);
 290                                 return map_all_fields(c, map_fields_userspace, "AUDIT_FIELD_", false, iov, n_iov_allocated, n_iov);
 291                         }
 292                 }
 293
 294                 /* Try to map the kernel fields to our own names */
 295                 for (m = map_fields; m->audit_field; m++) {
 296                         v = startswith(p, m->audit_field);
 297                         if (!v)
 298                                 continue;
 299
 300                         r = m->map(m->journal_field, &v, iov, n_iov_allocated, n_iov);
 301                         if (r < 0) {
 302                                 log_debug("Failed to parse audit array: %s", strerror(-r));
 303                                 return r;
 304                         }
 305
 306                         if (r > 0) {
 307                                 mapped = true;
 308                                 p = v;
 309                                 break;
 310                         }
 311                 }
 312
 313                 if (!mapped) {
 314                         r = map_generic_field(prefix, &p, iov, n_iov_allocated, n_iov);
 315                         if (r < 0) {
 316                                 log_debug("Failed to parse audit array: %s", strerror(-r));
 317                                 return r;
 318                         }
 319
 320                         if (r == 0) {
 321                                 /* Couldn't process as generic field, let's just skip over it */
 322                                 p += strcspn(p, WHITESPACE);
 323                         }
 324                 }
 325         }
 326 }
 327
 328 static void process_audit_string(Server *s, int type, const char *data, size_t size) {
 329         _cleanup_free_ struct iovec *iov = NULL;
 330         size_t n_iov_allocated = 0;
 331         unsigned n_iov = 0, k;
 332         uint64_t seconds, msec, id;
 333         const char *p;
 334         unsigned z;
 335         char id_field[sizeof("_AUDIT_ID=") + DECIMAL_STR_MAX(uint64_t)],
 336              type_field[sizeof("_AUDIT_TYPE=") + DECIMAL_STR_MAX(int)],
 337              source_time_field[sizeof("_SOURCE_REALTIME_TIMESTAMP=") + DECIMAL_STR_MAX(usec_t)];
 338         const char *m;
 339
 340         assert(s);
 341
 342         if (size <= 0)
 343                 return;
 344
 345         if (!data)
 346                 return;
 347
 348         /* Note that the input buffer is NUL terminated, but let's
 349          * check whether there is a spurious NUL byte */
 350         if (memchr(data, 0, size))
 351                 return;
 352
 353         p = startswith(data, "audit");
 354         if (!p)
 355                 return;
 356
 357         if (sscanf(p, "(%" PRIi64 ".%" PRIi64 ":%" PRIi64 "):%n",
 358                    &seconds,
 359                    &msec,
 360                    &id,
 361                    &k) != 3)
 362                 return;
 363
 364         p += k;
 365         p += strspn(p, WHITESPACE);
 366
 367         if (isempty(p))
 368                 return;
 369
 370         n_iov_allocated = N_IOVEC_META_FIELDS + 5;
 371         iov = new(struct iovec, n_iov_allocated);
 372         if (!iov) {
 373                 log_oom();
 374                 return;
 375         }
 376
 377         IOVEC_SET_STRING(iov[n_iov++], "_TRANSPORT=audit");
 378
 379         sprintf(source_time_field, "_SOURCE_REALTIME_TIMESTAMP=%" PRIu64,
 380                 (usec_t) seconds * USEC_PER_SEC + (usec_t) msec * USEC_PER_MSEC);
 381         IOVEC_SET_STRING(iov[n_iov++], source_time_field);
 382
 383         sprintf(type_field, "_AUDIT_TYPE=%i", type);
 384         IOVEC_SET_STRING(iov[n_iov++], type_field);
 385
 386         sprintf(id_field, "_AUDIT_ID=%" PRIu64, id);
 387         IOVEC_SET_STRING(iov[n_iov++], id_field);
 388
 389         m = strappenda("MESSAGE=audit: ", p);
 390         IOVEC_SET_STRING(iov[n_iov++], m);
 391
 392         z = n_iov;
 393
 394         map_all_fields(p, map_fields_kernel, "_AUDIT_FIELD_", true, &iov, &n_iov_allocated, &n_iov);
 395
 396         if (!GREEDY_REALLOC(iov, n_iov_allocated, n_iov + N_IOVEC_META_FIELDS)) {
 397                 log_oom();
 398                 goto finish;
 399         }
 400
 401         server_dispatch_message(s, iov, n_iov, n_iov_allocated, NULL, NULL, NULL, 0, NULL, LOG_NOTICE, 0);
 402
 403 finish:
 404         /* free() all entries that map_all_fields() added. All others
 405          * are allocated on the stack or are constant. */
 406
 407         for (; z < n_iov; z++)
 408                 free(iov[z].iov_base);
 409 }
 410
 411 void server_process_audit_message(
 412                 Server *s,
 413                 const void *buffer,
 414                 size_t buffer_size,
 415                 const struct ucred *ucred,
 416                 const union sockaddr_union *sa,
 417                 socklen_t salen) {
 418
 419         const struct nlmsghdr *nl = buffer;
 420
 421         assert(s);
 422
 423         if (buffer_size < ALIGN(sizeof(struct nlmsghdr)))
 424                 return;
 425
 426         assert(buffer);
 427
 428         /* Filter out fake data */
 429         if (!sa ||
 430             salen != sizeof(struct sockaddr_nl) ||
 431             sa->nl.nl_family != AF_NETLINK ||
 432             sa->nl.nl_pid != 0) {
 433                 log_debug("Audit netlink message from invalid sender.");
 434                 return;
 435         }
 436
 437         if (!ucred || ucred->pid != 0) {
 438                 log_debug("Audit netlink message with invalid credentials.");
 439                 return;
 440         }
 441
 442         if (!NLMSG_OK(nl, buffer_size)) {
 443                 log_error("Audit netlink message truncated.");
 444                 return;
 445         }
 446
 447         /* Ignore special Netlink messages */
 448         if (IN_SET(nl->nlmsg_type, NLMSG_NOOP, NLMSG_ERROR))
 449                 return;
 450
 451         /* Below AUDIT_FIRST_USER_MSG theer are only control messages, let's ignore those */
 452         if (nl->nlmsg_type < AUDIT_FIRST_USER_MSG)
 453                 return;
 454
 455         process_audit_string(s, nl->nlmsg_type, NLMSG_DATA(nl), nl->nlmsg_len - ALIGN(sizeof(struct nlmsghdr)));
 456 }
 457
 458 static int enable_audit(int fd, bool b) {
 459         struct {
 460                 union {
 461                         struct nlmsghdr header;
 462                         uint8_t header_space[NLMSG_HDRLEN];
 463                 };
 464                 struct audit_status body;
 465         } _packed_ request = {
 466                 .header.nlmsg_len = NLMSG_LENGTH(sizeof(struct audit_status)),
 467                 .header.nlmsg_type = AUDIT_SET,
 468                 .header.nlmsg_flags = NLM_F_REQUEST,
 469                 .header.nlmsg_seq = 1,
 470                 .header.nlmsg_pid = 0,
 471                 .body.mask = AUDIT_STATUS_ENABLED,
 472                 .body.enabled = b,
 473         };
 474         union sockaddr_union sa = {
 475                 .nl.nl_family = AF_NETLINK,
 476                 .nl.nl_pid = 0,
 477         };
 478         struct iovec iovec = {
 479                 .iov_base = &request,
 480                 .iov_len = NLMSG_LENGTH(sizeof(struct audit_status)),
 481         };
 482         struct msghdr mh = {
 483                 .msg_iov = &iovec,
 484                 .msg_iovlen = 1,
 485                 .msg_name = &sa.sa,
 486                 .msg_namelen = sizeof(sa.nl),
 487         };
 488
 489         ssize_t n;
 490
 491         n = sendmsg(fd, &mh, MSG_NOSIGNAL);
 492         if (n < 0)
 493                 return -errno;
 494         if (n != NLMSG_LENGTH(sizeof(struct audit_status)))
 495                 return -EIO;
 496
 497         /* We don't wait for the result here, we can't do anything
 498          * about it anyway */
 499
 500         return 0;
 501 }
 502
 503 int server_open_audit(Server *s) {
 504         static const int one = 1;
 505         int r;
 506
 507         if (s->audit_fd < 0) {
 508                 static const union sockaddr_union sa = {
 509                         .nl.nl_family = AF_NETLINK,
 510                         .nl.nl_pid    = 0,
 511                         .nl.nl_groups = AUDIT_NLGRP_READLOG,
 512                 };
 513
 514                 s->audit_fd = socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_AUDIT);
 515                 if (s->audit_fd < 0) {
 516                         if (errno == EAFNOSUPPORT || errno == EPROTONOSUPPORT)
 517                                 log_debug("Audit not supported in the kernel.");
 518                         else
 519                                 log_warning("Failed to create audit socket, ignoring: %m");
 520
 521                         return 0;
 522                 }
 523
 524                 r = bind(s->audit_fd, &sa.sa, sizeof(sa.nl));
 525                 if (r < 0) {
 526                         log_error("Failed to join audit multicast group: %m");
 527                         return -errno;
 528                 }
 529         } else
 530                 fd_nonblock(s->audit_fd, 1);
 531
 532         r = setsockopt(s->audit_fd, SOL_SOCKET, SO_PASSCRED, &one, sizeof(one));
 533         if (r < 0) {
 534                 log_error("Failed to set SO_PASSCRED on audit socket: %m");
 535                 return -errno;
 536         }
 537
 538         r = sd_event_add_io(s->event, &s->audit_event_source, s->audit_fd, EPOLLIN, process_datagram, s);
 539         if (r < 0) {
 540                 log_error("Failed to add audit fd to event loop: %s", strerror(-r));
 541                 return r;
 542         }
 543
 544         /* We are listening now, try to enable audit */
 545         r = enable_audit(s->audit_fd, true);
 546         if (r < 0)
 547                 log_warning("Failed to issue audit enable call: %s", strerror(-r));
 548
 549         return 0;
 550 }