security/apparmor/match.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * AppArmor security module
   4  *
   5  * This file contains AppArmor dfa based regular expression matching engine
   6  *
   7  * Copyright (C) 1998-2008 Novell/SUSE
   8  * Copyright 2009-2012 Canonical Ltd.
   9  */
  10
  11 #include <linux/errno.h>
  12 #include <linux/kernel.h>
  13 #include <linux/mm.h>
  14 #include <linux/slab.h>
  15 #include <linux/vmalloc.h>
  16 #include <linux/err.h>
  17 #include <linux/kref.h>
  18
  19 #include "include/lib.h"
  20 #include "include/match.h"
  21
  22 #define base_idx(X) ((X) & 0xffffff)
  23
  24 static char nulldfa_src[] = {
  25         #include "nulldfa.in"
  26 };
  27 struct aa_dfa *nulldfa;
  28
  29 static char stacksplitdfa_src[] = {
  30         #include "stacksplitdfa.in"
  31 };
  32 struct aa_dfa *stacksplitdfa;
  33
  34 int aa_setup_dfa_engine(void)
  35 {
  36         int error;
  37
  38         nulldfa = aa_dfa_unpack(nulldfa_src, sizeof(nulldfa_src),
  39                                 TO_ACCEPT1_FLAG(YYTD_DATA32) |
  40                                 TO_ACCEPT2_FLAG(YYTD_DATA32));
  41         if (IS_ERR(nulldfa)) {
  42                 error = PTR_ERR(nulldfa);
  43                 nulldfa = NULL;
  44                 return error;
  45         }
  46
  47         stacksplitdfa = aa_dfa_unpack(stacksplitdfa_src,
  48                                       sizeof(stacksplitdfa_src),
  49                                       TO_ACCEPT1_FLAG(YYTD_DATA32) |
  50                                       TO_ACCEPT2_FLAG(YYTD_DATA32));
  51         if (IS_ERR(stacksplitdfa)) {
  52                 aa_put_dfa(nulldfa);
  53                 nulldfa = NULL;
  54                 error = PTR_ERR(stacksplitdfa);
  55                 stacksplitdfa = NULL;
  56                 return error;
  57         }
  58
  59         return 0;
  60 }
  61
  62 void aa_teardown_dfa_engine(void)
  63 {
  64         aa_put_dfa(stacksplitdfa);
  65         aa_put_dfa(nulldfa);
  66 }
  67
  68 /**
  69  * unpack_table - unpack a dfa table (one of accept, default, base, next check)
  70  * @blob: data to unpack (NOT NULL)
  71  * @bsize: size of blob
  72  *
  73  * Returns: pointer to table else NULL on failure
  74  *
  75  * NOTE: must be freed by kvfree (not kfree)
  76  */
  77 static struct table_header *unpack_table(char *blob, size_t bsize)
  78 {
  79         struct table_header *table = NULL;
  80         struct table_header th;
  81         size_t tsize;
  82
  83         if (bsize < sizeof(struct table_header))
  84                 goto out;
  85
  86         /* loaded td_id's start at 1, subtract 1 now to avoid doing
  87          * it every time we use td_id as an index
  88          */
  89         th.td_id = be16_to_cpu(*(__be16 *) (blob)) - 1;
  90         if (th.td_id > YYTD_ID_MAX)
  91                 goto out;
  92         th.td_flags = be16_to_cpu(*(__be16 *) (blob + 2));
  93         th.td_lolen = be32_to_cpu(*(__be32 *) (blob + 8));
  94         blob += sizeof(struct table_header);
  95
  96         if (!(th.td_flags == YYTD_DATA16 || th.td_flags == YYTD_DATA32 ||
  97               th.td_flags == YYTD_DATA8))
  98                 goto out;
  99
 100         tsize = table_size(th.td_lolen, th.td_flags);
 101         if (bsize < tsize)
 102                 goto out;
 103
 104         table = kvzalloc(tsize, GFP_KERNEL);
 105         if (table) {
 106                 table->td_id = th.td_id;
 107                 table->td_flags = th.td_flags;
 108                 table->td_lolen = th.td_lolen;
 109                 if (th.td_flags == YYTD_DATA8)
 110                         UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
 111                                      u8, u8, byte_to_byte);
 112                 else if (th.td_flags == YYTD_DATA16)
 113                         UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
 114                                      u16, __be16, be16_to_cpu);
 115                 else if (th.td_flags == YYTD_DATA32)
 116                         UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
 117                                      u32, __be32, be32_to_cpu);
 118                 else
 119                         goto fail;
 120                 /* if table was vmalloced make sure the page tables are synced
 121                  * before it is used, as it goes live to all cpus.
 122                  */
 123                 if (is_vmalloc_addr(table))
 124                         vm_unmap_aliases();
 125         }
 126
 127 out:
 128         return table;
 129 fail:
 130         kvfree(table);
 131         return NULL;
 132 }
 133
 134 /**
 135  * verify_table_headers - verify that the tables headers are as expected
 136  * @tables - array of dfa tables to check (NOT NULL)
 137  * @flags: flags controlling what type of accept table are acceptable
 138  *
 139  * Assumes dfa has gone through the first pass verification done by unpacking
 140  * NOTE: this does not valid accept table values
 141  *
 142  * Returns: %0 else error code on failure to verify
 143  */
 144 static int verify_table_headers(struct table_header **tables, int flags)
 145 {
 146         size_t state_count, trans_count;
 147         int error = -EPROTO;
 148
 149         /* check that required tables exist */
 150         if (!(tables[YYTD_ID_DEF] && tables[YYTD_ID_BASE] &&
 151               tables[YYTD_ID_NXT] && tables[YYTD_ID_CHK]))
 152                 goto out;
 153
 154         /* accept.size == default.size == base.size */
 155         state_count = tables[YYTD_ID_BASE]->td_lolen;
 156         if (ACCEPT1_FLAGS(flags)) {
 157                 if (!tables[YYTD_ID_ACCEPT])
 158                         goto out;
 159                 if (state_count != tables[YYTD_ID_ACCEPT]->td_lolen)
 160                         goto out;
 161         }
 162         if (ACCEPT2_FLAGS(flags)) {
 163                 if (!tables[YYTD_ID_ACCEPT2])
 164                         goto out;
 165                 if (state_count != tables[YYTD_ID_ACCEPT2]->td_lolen)
 166                         goto out;
 167         }
 168         if (state_count != tables[YYTD_ID_DEF]->td_lolen)
 169                 goto out;
 170
 171         /* next.size == chk.size */
 172         trans_count = tables[YYTD_ID_NXT]->td_lolen;
 173         if (trans_count != tables[YYTD_ID_CHK]->td_lolen)
 174                 goto out;
 175
 176         /* if equivalence classes then its table size must be 256 */
 177         if (tables[YYTD_ID_EC] && tables[YYTD_ID_EC]->td_lolen != 256)
 178                 goto out;
 179
 180         error = 0;
 181 out:
 182         return error;
 183 }
 184
 185 /**
 186  * verify_dfa - verify that transitions and states in the tables are in bounds.
 187  * @dfa: dfa to test  (NOT NULL)
 188  *
 189  * Assumes dfa has gone through the first pass verification done by unpacking
 190  * NOTE: this does not valid accept table values
 191  *
 192  * Returns: %0 else error code on failure to verify
 193  */
 194 static int verify_dfa(struct aa_dfa *dfa)
 195 {
 196         size_t i, state_count, trans_count;
 197         int error = -EPROTO;
 198
 199         state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
 200         trans_count = dfa->tables[YYTD_ID_NXT]->td_lolen;
 201         for (i = 0; i < state_count; i++) {
 202                 if (!(BASE_TABLE(dfa)[i] & MATCH_FLAG_DIFF_ENCODE) &&
 203                     (DEFAULT_TABLE(dfa)[i] >= state_count))
 204                         goto out;
 205                 if (base_idx(BASE_TABLE(dfa)[i]) + 255 >= trans_count) {
 206                         pr_err("AppArmor DFA next/check upper bounds error\n");
 207                         goto out;
 208                 }
 209         }
 210
 211         for (i = 0; i < trans_count; i++) {
 212                 if (NEXT_TABLE(dfa)[i] >= state_count)
 213                         goto out;
 214                 if (CHECK_TABLE(dfa)[i] >= state_count)
 215                         goto out;
 216         }
 217
 218         /* Now that all the other tables are verified, verify diffencoding */
 219         for (i = 0; i < state_count; i++) {
 220                 size_t j, k;
 221
 222                 for (j = i;
 223                      (BASE_TABLE(dfa)[j] & MATCH_FLAG_DIFF_ENCODE) &&
 224                      !(BASE_TABLE(dfa)[j] & MARK_DIFF_ENCODE);
 225                      j = k) {
 226                         k = DEFAULT_TABLE(dfa)[j];
 227                         if (j == k)
 228                                 goto out;
 229                         if (k < j)
 230                                 break;          /* already verified */
 231                         BASE_TABLE(dfa)[j] |= MARK_DIFF_ENCODE;
 232                 }
 233         }
 234         error = 0;
 235
 236 out:
 237         return error;
 238 }
 239
 240 /**
 241  * dfa_free - free a dfa allocated by aa_dfa_unpack
 242  * @dfa: the dfa to free  (MAYBE NULL)
 243  *
 244  * Requires: reference count to dfa == 0
 245  */
 246 static void dfa_free(struct aa_dfa *dfa)
 247 {
 248         if (dfa) {
 249                 int i;
 250
 251                 for (i = 0; i < ARRAY_SIZE(dfa->tables); i++) {
 252                         kvfree(dfa->tables[i]);
 253                         dfa->tables[i] = NULL;
 254                 }
 255                 kfree(dfa);
 256         }
 257 }
 258
 259 /**
 260  * aa_dfa_free_kref - free aa_dfa by kref (called by aa_put_dfa)
 261  * @kr: kref callback for freeing of a dfa  (NOT NULL)
 262  */
 263 void aa_dfa_free_kref(struct kref *kref)
 264 {
 265         struct aa_dfa *dfa = container_of(kref, struct aa_dfa, count);
 266         dfa_free(dfa);
 267 }
 268
 269 /**
 270  * aa_dfa_unpack - unpack the binary tables of a serialized dfa
 271  * @blob: aligned serialized stream of data to unpack  (NOT NULL)
 272  * @size: size of data to unpack
 273  * @flags: flags controlling what type of accept tables are acceptable
 274  *
 275  * Unpack a dfa that has been serialized.  To find information on the dfa
 276  * format look in Documentation/admin-guide/LSM/apparmor.rst
 277  * Assumes the dfa @blob stream has been aligned on a 8 byte boundary
 278  *
 279  * Returns: an unpacked dfa ready for matching or ERR_PTR on failure
 280  */
 281 struct aa_dfa *aa_dfa_unpack(void *blob, size_t size, int flags)
 282 {
 283         int hsize;
 284         int error = -ENOMEM;
 285         char *data = blob;
 286         struct table_header *table = NULL;
 287         struct aa_dfa *dfa = kzalloc(sizeof(struct aa_dfa), GFP_KERNEL);
 288         if (!dfa)
 289                 goto fail;
 290
 291         kref_init(&dfa->count);
 292
 293         error = -EPROTO;
 294
 295         /* get dfa table set header */
 296         if (size < sizeof(struct table_set_header))
 297                 goto fail;
 298
 299         if (ntohl(*(__be32 *) data) != YYTH_MAGIC)
 300                 goto fail;
 301
 302         hsize = ntohl(*(__be32 *) (data + 4));
 303         if (size < hsize)
 304                 goto fail;
 305
 306         dfa->flags = ntohs(*(__be16 *) (data + 12));
 307         if (dfa->flags != 0 && dfa->flags != YYTH_FLAG_DIFF_ENCODE)
 308                 goto fail;
 309
 310         data += hsize;
 311         size -= hsize;
 312
 313         while (size > 0) {
 314                 table = unpack_table(data, size);
 315                 if (!table)
 316                         goto fail;
 317
 318                 switch (table->td_id) {
 319                 case YYTD_ID_ACCEPT:
 320                         if (!(table->td_flags & ACCEPT1_FLAGS(flags)))
 321                                 goto fail;
 322                         break;
 323                 case YYTD_ID_ACCEPT2:
 324                         if (!(table->td_flags & ACCEPT2_FLAGS(flags)))
 325                                 goto fail;
 326                         break;
 327                 case YYTD_ID_BASE:
 328                         if (table->td_flags != YYTD_DATA32)
 329                                 goto fail;
 330                         break;
 331                 case YYTD_ID_DEF:
 332                 case YYTD_ID_NXT:
 333                 case YYTD_ID_CHK:
 334                         if (table->td_flags != YYTD_DATA16)
 335                                 goto fail;
 336                         break;
 337                 case YYTD_ID_EC:
 338                         if (table->td_flags != YYTD_DATA8)
 339                                 goto fail;
 340                         break;
 341                 default:
 342                         goto fail;
 343                 }
 344                 /* check for duplicate table entry */
 345                 if (dfa->tables[table->td_id])
 346                         goto fail;
 347                 dfa->tables[table->td_id] = table;
 348                 data += table_size(table->td_lolen, table->td_flags);
 349                 size -= table_size(table->td_lolen, table->td_flags);
 350                 table = NULL;
 351         }
 352         error = verify_table_headers(dfa->tables, flags);
 353         if (error)
 354                 goto fail;
 355
 356         if (flags & DFA_FLAG_VERIFY_STATES) {
 357                 error = verify_dfa(dfa);
 358                 if (error)
 359                         goto fail;
 360         }
 361
 362         return dfa;
 363
 364 fail:
 365         kvfree(table);
 366         dfa_free(dfa);
 367         return ERR_PTR(error);
 368 }
 369
 370 #define match_char(state, def, base, next, check, C)    \
 371 do {                                                    \
 372         u32 b = (base)[(state)];                        \
 373         unsigned int pos = base_idx(b) + (C);           \
 374         if ((check)[pos] != (state)) {                  \
 375                 (state) = (def)[(state)];               \
 376                 if (b & MATCH_FLAG_DIFF_ENCODE)         \
 377                         continue;                       \
 378                 break;                                  \
 379         }                                               \
 380         (state) = (next)[pos];                          \
 381         break;                                          \
 382 } while (1)
 383
 384 /**
 385  * aa_dfa_match_len - traverse @dfa to find state @str stops at
 386  * @dfa: the dfa to match @str against  (NOT NULL)
 387  * @start: the state of the dfa to start matching in
 388  * @str: the string of bytes to match against the dfa  (NOT NULL)
 389  * @len: length of the string of bytes to match
 390  *
 391  * aa_dfa_match_len will match @str against the dfa and return the state it
 392  * finished matching in. The final state can be used to look up the accepting
 393  * label, or as the start state of a continuing match.
 394  *
 395  * This function will happily match again the 0 byte and only finishes
 396  * when @len input is consumed.
 397  *
 398  * Returns: final state reached after input is consumed
 399  */
 400 unsigned int aa_dfa_match_len(struct aa_dfa *dfa, unsigned int start,
 401                               const char *str, int len)
 402 {
 403         u16 *def = DEFAULT_TABLE(dfa);
 404         u32 *base = BASE_TABLE(dfa);
 405         u16 *next = NEXT_TABLE(dfa);
 406         u16 *check = CHECK_TABLE(dfa);
 407         unsigned int state = start;
 408
 409         if (state == 0)
 410                 return 0;
 411
 412         /* current state is <state>, matching character *str */
 413         if (dfa->tables[YYTD_ID_EC]) {
 414                 /* Equivalence class table defined */
 415                 u8 *equiv = EQUIV_TABLE(dfa);
 416                 for (; len; len--)
 417                         match_char(state, def, base, next, check,
 418                                    equiv[(u8) *str++]);
 419         } else {
 420                 /* default is direct to next state */
 421                 for (; len; len--)
 422                         match_char(state, def, base, next, check, (u8) *str++);
 423         }
 424
 425         return state;
 426 }
 427
 428 /**
 429  * aa_dfa_match - traverse @dfa to find state @str stops at
 430  * @dfa: the dfa to match @str against  (NOT NULL)
 431  * @start: the state of the dfa to start matching in
 432  * @str: the null terminated string of bytes to match against the dfa (NOT NULL)
 433  *
 434  * aa_dfa_match will match @str against the dfa and return the state it
 435  * finished matching in. The final state can be used to look up the accepting
 436  * label, or as the start state of a continuing match.
 437  *
 438  * Returns: final state reached after input is consumed
 439  */
 440 unsigned int aa_dfa_match(struct aa_dfa *dfa, unsigned int start,
 441                           const char *str)
 442 {
 443         u16 *def = DEFAULT_TABLE(dfa);
 444         u32 *base = BASE_TABLE(dfa);
 445         u16 *next = NEXT_TABLE(dfa);
 446         u16 *check = CHECK_TABLE(dfa);
 447         unsigned int state = start;
 448
 449         if (state == 0)
 450                 return 0;
 451
 452         /* current state is <state>, matching character *str */
 453         if (dfa->tables[YYTD_ID_EC]) {
 454                 /* Equivalence class table defined */
 455                 u8 *equiv = EQUIV_TABLE(dfa);
 456                 /* default is direct to next state */
 457                 while (*str)
 458                         match_char(state, def, base, next, check,
 459                                    equiv[(u8) *str++]);
 460         } else {
 461                 /* default is direct to next state */
 462                 while (*str)
 463                         match_char(state, def, base, next, check, (u8) *str++);
 464         }
 465
 466         return state;
 467 }
 468
 469 /**
 470  * aa_dfa_next - step one character to the next state in the dfa
 471  * @dfa: the dfa to traverse (NOT NULL)
 472  * @state: the state to start in
 473  * @c: the input character to transition on
 474  *
 475  * aa_dfa_match will step through the dfa by one input character @c
 476  *
 477  * Returns: state reach after input @c
 478  */
 479 unsigned int aa_dfa_next(struct aa_dfa *dfa, unsigned int state,
 480                           const char c)
 481 {
 482         u16 *def = DEFAULT_TABLE(dfa);
 483         u32 *base = BASE_TABLE(dfa);
 484         u16 *next = NEXT_TABLE(dfa);
 485         u16 *check = CHECK_TABLE(dfa);
 486
 487         /* current state is <state>, matching character *str */
 488         if (dfa->tables[YYTD_ID_EC]) {
 489                 /* Equivalence class table defined */
 490                 u8 *equiv = EQUIV_TABLE(dfa);
 491                 match_char(state, def, base, next, check, equiv[(u8) c]);
 492         } else
 493                 match_char(state, def, base, next, check, (u8) c);
 494
 495         return state;
 496 }
 497
 498 /**
 499  * aa_dfa_match_until - traverse @dfa until accept state or end of input
 500  * @dfa: the dfa to match @str against  (NOT NULL)
 501  * @start: the state of the dfa to start matching in
 502  * @str: the null terminated string of bytes to match against the dfa (NOT NULL)
 503  * @retpos: first character in str after match OR end of string
 504  *
 505  * aa_dfa_match will match @str against the dfa and return the state it
 506  * finished matching in. The final state can be used to look up the accepting
 507  * label, or as the start state of a continuing match.
 508  *
 509  * Returns: final state reached after input is consumed
 510  */
 511 unsigned int aa_dfa_match_until(struct aa_dfa *dfa, unsigned int start,
 512                                 const char *str, const char **retpos)
 513 {
 514         u16 *def = DEFAULT_TABLE(dfa);
 515         u32 *base = BASE_TABLE(dfa);
 516         u16 *next = NEXT_TABLE(dfa);
 517         u16 *check = CHECK_TABLE(dfa);
 518         u32 *accept = ACCEPT_TABLE(dfa);
 519         unsigned int state = start, pos;
 520
 521         if (state == 0)
 522                 return 0;
 523
 524         /* current state is <state>, matching character *str */
 525         if (dfa->tables[YYTD_ID_EC]) {
 526                 /* Equivalence class table defined */
 527                 u8 *equiv = EQUIV_TABLE(dfa);
 528                 /* default is direct to next state */
 529                 while (*str) {
 530                         pos = base_idx(base[state]) + equiv[(u8) *str++];
 531                         if (check[pos] == state)
 532                                 state = next[pos];
 533                         else
 534                                 state = def[state];
 535                         if (accept[state])
 536                                 break;
 537                 }
 538         } else {
 539                 /* default is direct to next state */
 540                 while (*str) {
 541                         pos = base_idx(base[state]) + (u8) *str++;
 542                         if (check[pos] == state)
 543                                 state = next[pos];
 544                         else
 545                                 state = def[state];
 546                         if (accept[state])
 547                                 break;
 548                 }
 549         }
 550
 551         *retpos = str;
 552         return state;
 553 }
 554
 555 /**
 556  * aa_dfa_matchn_until - traverse @dfa until accept or @n bytes consumed
 557  * @dfa: the dfa to match @str against  (NOT NULL)
 558  * @start: the state of the dfa to start matching in
 559  * @str: the string of bytes to match against the dfa  (NOT NULL)
 560  * @n: length of the string of bytes to match
 561  * @retpos: first character in str after match OR str + n
 562  *
 563  * aa_dfa_match_len will match @str against the dfa and return the state it
 564  * finished matching in. The final state can be used to look up the accepting
 565  * label, or as the start state of a continuing match.
 566  *
 567  * This function will happily match again the 0 byte and only finishes
 568  * when @n input is consumed.
 569  *
 570  * Returns: final state reached after input is consumed
 571  */
 572 unsigned int aa_dfa_matchn_until(struct aa_dfa *dfa, unsigned int start,
 573                                  const char *str, int n, const char **retpos)
 574 {
 575         u16 *def = DEFAULT_TABLE(dfa);
 576         u32 *base = BASE_TABLE(dfa);
 577         u16 *next = NEXT_TABLE(dfa);
 578         u16 *check = CHECK_TABLE(dfa);
 579         u32 *accept = ACCEPT_TABLE(dfa);
 580         unsigned int state = start, pos;
 581
 582         *retpos = NULL;
 583         if (state == 0)
 584                 return 0;
 585
 586         /* current state is <state>, matching character *str */
 587         if (dfa->tables[YYTD_ID_EC]) {
 588                 /* Equivalence class table defined */
 589                 u8 *equiv = EQUIV_TABLE(dfa);
 590                 /* default is direct to next state */
 591                 for (; n; n--) {
 592                         pos = base_idx(base[state]) + equiv[(u8) *str++];
 593                         if (check[pos] == state)
 594                                 state = next[pos];
 595                         else
 596                                 state = def[state];
 597                         if (accept[state])
 598                                 break;
 599                 }
 600         } else {
 601                 /* default is direct to next state */
 602                 for (; n; n--) {
 603                         pos = base_idx(base[state]) + (u8) *str++;
 604                         if (check[pos] == state)
 605                                 state = next[pos];
 606                         else
 607                                 state = def[state];
 608                         if (accept[state])
 609                                 break;
 610                 }
 611         }
 612
 613         *retpos = str;
 614         return state;
 615 }
 616
 617 #define inc_wb_pos(wb)                                          \
 618 do {                                                            \
 619         wb->pos = (wb->pos + 1) & (WB_HISTORY_SIZE - 1);                \
 620         wb->len = (wb->len + 1) & (WB_HISTORY_SIZE - 1);                \
 621 } while (0)
 622
 623 /* For DFAs that don't support extended tagging of states */
 624 static bool is_loop(struct match_workbuf *wb, unsigned int state,
 625                     unsigned int *adjust)
 626 {
 627         unsigned int pos = wb->pos;
 628         unsigned int i;
 629
 630         if (wb->history[pos] < state)
 631                 return false;
 632
 633         for (i = 0; i <= wb->len; i++) {
 634                 if (wb->history[pos] == state) {
 635                         *adjust = i;
 636                         return true;
 637                 }
 638                 if (pos == 0)
 639                         pos = WB_HISTORY_SIZE;
 640                 pos--;
 641         }
 642
 643         *adjust = i;
 644         return true;
 645 }
 646
 647 static unsigned int leftmatch_fb(struct aa_dfa *dfa, unsigned int start,
 648                                  const char *str, struct match_workbuf *wb,
 649                                  unsigned int *count)
 650 {
 651         u16 *def = DEFAULT_TABLE(dfa);
 652         u32 *base = BASE_TABLE(dfa);
 653         u16 *next = NEXT_TABLE(dfa);
 654         u16 *check = CHECK_TABLE(dfa);
 655         unsigned int state = start, pos;
 656
 657         AA_BUG(!dfa);
 658         AA_BUG(!str);
 659         AA_BUG(!wb);
 660         AA_BUG(!count);
 661
 662         *count = 0;
 663         if (state == 0)
 664                 return 0;
 665
 666         /* current state is <state>, matching character *str */
 667         if (dfa->tables[YYTD_ID_EC]) {
 668                 /* Equivalence class table defined */
 669                 u8 *equiv = EQUIV_TABLE(dfa);
 670                 /* default is direct to next state */
 671                 while (*str) {
 672                         unsigned int adjust;
 673
 674                         wb->history[wb->pos] = state;
 675                         pos = base_idx(base[state]) + equiv[(u8) *str++];
 676                         if (check[pos] == state)
 677                                 state = next[pos];
 678                         else
 679                                 state = def[state];
 680                         if (is_loop(wb, state, &adjust)) {
 681                                 state = aa_dfa_match(dfa, state, str);
 682                                 *count -= adjust;
 683                                 goto out;
 684                         }
 685                         inc_wb_pos(wb);
 686                         (*count)++;
 687                 }
 688         } else {
 689                 /* default is direct to next state */
 690                 while (*str) {
 691                         unsigned int adjust;
 692
 693                         wb->history[wb->pos] = state;
 694                         pos = base_idx(base[state]) + (u8) *str++;
 695                         if (check[pos] == state)
 696                                 state = next[pos];
 697                         else
 698                                 state = def[state];
 699                         if (is_loop(wb, state, &adjust)) {
 700                                 state = aa_dfa_match(dfa, state, str);
 701                                 *count -= adjust;
 702                                 goto out;
 703                         }
 704                         inc_wb_pos(wb);
 705                         (*count)++;
 706                 }
 707         }
 708
 709 out:
 710         if (!state)
 711                 *count = 0;
 712         return state;
 713 }
 714
 715 /**
 716  * aa_dfa_leftmatch - traverse @dfa to find state @str stops at
 717  * @dfa: the dfa to match @str against  (NOT NULL)
 718  * @start: the state of the dfa to start matching in
 719  * @str: the null terminated string of bytes to match against the dfa (NOT NULL)
 720  * @count: current count of longest left.
 721  *
 722  * aa_dfa_match will match @str against the dfa and return the state it
 723  * finished matching in. The final state can be used to look up the accepting
 724  * label, or as the start state of a continuing match.
 725  *
 726  * Returns: final state reached after input is consumed
 727  */
 728 unsigned int aa_dfa_leftmatch(struct aa_dfa *dfa, unsigned int start,
 729                               const char *str, unsigned int *count)
 730 {
 731         DEFINE_MATCH_WB(wb);
 732
 733         /* TODO: match for extended state dfas */
 734
 735         return leftmatch_fb(dfa, start, str, &wb, count);
 736 }