summaryrefslogtreecommitdiff
path: root/security/apparmor/match.c
blob: e605b7d53fb4b632d15380881d3132d1a24836b4 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
// SPDX-License-Identifier: GPL-2.0-only
/*
 * AppArmor security module
 *
 * This file contains AppArmor dfa based regular expression matching engine
 *
 * Copyright (C) 1998-2008 Novell/SUSE
 * Copyright 2009-2012 Canonical Ltd.
 */

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/err.h>
#include <linux/kref.h>

#include "include/lib.h"
#include "include/match.h"

#define base_idx(X) ((X) & 0xffffff)

static char nulldfa_src[] = {
	#include "nulldfa.in"
};
struct aa_dfa *nulldfa;

static char stacksplitdfa_src[] = {
	#include "stacksplitdfa.in"
};
struct aa_dfa *stacksplitdfa;

int aa_setup_dfa_engine(void)
{
	int error;

	nulldfa = aa_dfa_unpack(nulldfa_src, sizeof(nulldfa_src),
				TO_ACCEPT1_FLAG(YYTD_DATA32) |
				TO_ACCEPT2_FLAG(YYTD_DATA32));
	if (IS_ERR(nulldfa)) {
		error = PTR_ERR(nulldfa);
		nulldfa = NULL;
		return error;
	}

	stacksplitdfa = aa_dfa_unpack(stacksplitdfa_src,
				      sizeof(stacksplitdfa_src),
				      TO_ACCEPT1_FLAG(YYTD_DATA32) |
				      TO_ACCEPT2_FLAG(YYTD_DATA32));
	if (IS_ERR(stacksplitdfa)) {
		aa_put_dfa(nulldfa);
		nulldfa = NULL;
		error = PTR_ERR(stacksplitdfa);
		stacksplitdfa = NULL;
		return error;
	}

	return 0;
}

void aa_teardown_dfa_engine(void)
{
	aa_put_dfa(stacksplitdfa);
	aa_put_dfa(nulldfa);
}

/**
 * unpack_table - unpack a dfa table (one of accept, default, base, next check)
 * @blob: data to unpack (NOT NULL)
 * @bsize: size of blob
 *
 * Returns: pointer to table else NULL on failure
 *
 * NOTE: must be freed by kvfree (not kfree)
 */
static struct table_header *unpack_table(char *blob, size_t bsize)
{
	struct table_header *table = NULL;
	struct table_header th;
	size_t tsize;

	if (bsize < sizeof(struct table_header))
		goto out;

	/* loaded td_id's start at 1, subtract 1 now to avoid doing
	 * it every time we use td_id as an index
	 */
	th.td_id = be16_to_cpu(*(__be16 *) (blob)) - 1;
	if (th.td_id > YYTD_ID_MAX)
		goto out;
	th.td_flags = be16_to_cpu(*(__be16 *) (blob + 2));
	th.td_lolen = be32_to_cpu(*(__be32 *) (blob + 8));
	blob += sizeof(struct table_header);

	if (!(th.td_flags == YYTD_DATA16 || th.td_flags == YYTD_DATA32 ||
	      th.td_flags == YYTD_DATA8))
		goto out;

	tsize = table_size(th.td_lolen, th.td_flags);
	if (bsize < tsize)
		goto out;

	table = kvzalloc(tsize, GFP_KERNEL);
	if (table) {
		table->td_id = th.td_id;
		table->td_flags = th.td_flags;
		table->td_lolen = th.td_lolen;
		if (th.td_flags == YYTD_DATA8)
			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
				     u8, u8, byte_to_byte);
		else if (th.td_flags == YYTD_DATA16)
			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
				     u16, __be16, be16_to_cpu);
		else if (th.td_flags == YYTD_DATA32)
			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
				     u32, __be32, be32_to_cpu);
		else
			goto fail;
		/* if table was vmalloced make sure the page tables are synced
		 * before it is used, as it goes live to all cpus.
		 */
		if (is_vmalloc_addr(table))
			vm_unmap_aliases();
	}

out:
	return table;
fail:
	kvfree(table);
	return NULL;
}

/**
 * verify_table_headers - verify that the tables headers are as expected
 * @tables - array of dfa tables to check (NOT NULL)
 * @flags: flags controlling what type of accept table are acceptable
 *
 * Assumes dfa has gone through the first pass verification done by unpacking
 * NOTE: this does not valid accept table values
 *
 * Returns: %0 else error code on failure to verify
 */
static int verify_table_headers(struct table_header **tables, int flags)
{
	size_t state_count, trans_count;
	int error = -EPROTO;

	/* check that required tables exist */
	if (!(tables[YYTD_ID_DEF] && tables[YYTD_ID_BASE] &&
	      tables[YYTD_ID_NXT] && tables[YYTD_ID_CHK]))
		goto out;

	/* accept.size == default.size == base.size */
	state_count = tables[YYTD_ID_BASE]->td_lolen;
	if (ACCEPT1_FLAGS(flags)) {
		if (!tables[YYTD_ID_ACCEPT])
			goto out;
		if (state_count != tables[YYTD_ID_ACCEPT]->td_lolen)
			goto out;
	}
	if (ACCEPT2_FLAGS(flags)) {
		if (!tables[YYTD_ID_ACCEPT2])
			goto out;
		if (state_count != tables[YYTD_ID_ACCEPT2]->td_lolen)
			goto out;
	}
	if (state_count != tables[YYTD_ID_DEF]->td_lolen)
		goto out;

	/* next.size == chk.size */
	trans_count = tables[YYTD_ID_NXT]->td_lolen;
	if (trans_count != tables[YYTD_ID_CHK]->td_lolen)
		goto out;

	/* if equivalence classes then its table size must be 256 */
	if (tables[YYTD_ID_EC] && tables[YYTD_ID_EC]->td_lolen != 256)
		goto out;

	error = 0;
out:
	return error;
}

/**
 * verify_dfa - verify that transitions and states in the tables are in bounds.
 * @dfa: dfa to test  (NOT NULL)
 *
 * Assumes dfa has gone through the first pass verification done by unpacking
 * NOTE: this does not valid accept table values
 *
 * Returns: %0 else error code on failure to verify
 */
static int verify_dfa(struct aa_dfa *dfa)
{
	size_t i, state_count, trans_count;
	int error = -EPROTO;

	state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
	trans_count = dfa->tables[YYTD_ID_NXT]->td_lolen;
	for (i = 0; i < state_count; i++) {
		if (!(BASE_TABLE(dfa)[i] & MATCH_FLAG_DIFF_ENCODE) &&
		    (DEFAULT_TABLE(dfa)[i] >= state_count))
			goto out;
		if (BASE_TABLE(dfa)[i] & MATCH_FLAGS_INVALID) {
			pr_err("AppArmor DFA state with invalid match flags");
			goto out;
		}
		if ((BASE_TABLE(dfa)[i] & MATCH_FLAG_DIFF_ENCODE)) {
			if (!(dfa->flags & YYTH_FLAG_DIFF_ENCODE)) {
				pr_err("AppArmor DFA diff encoded transition state without header flag");
				goto out;
			}
		}
		if ((BASE_TABLE(dfa)[i] & MATCH_FLAG_OOB_TRANSITION)) {
			if (base_idx(BASE_TABLE(dfa)[i]) < dfa->max_oob) {
				pr_err("AppArmor DFA out of bad transition out of range");
				goto out;
			}
			if (!(dfa->flags & YYTH_FLAG_OOB_TRANS)) {
				pr_err("AppArmor DFA out of bad transition state without header flag");
				goto out;
			}
		}
		if (base_idx(BASE_TABLE(dfa)[i]) + 255 >= trans_count) {
			pr_err("AppArmor DFA next/check upper bounds error\n");
			goto out;
		}
	}

	for (i = 0; i < trans_count; i++) {
		if (NEXT_TABLE(dfa)[i] >= state_count)
			goto out;
		if (CHECK_TABLE(dfa)[i] >= state_count)
			goto out;
	}

	/* Now that all the other tables are verified, verify diffencoding */
	for (i = 0; i < state_count; i++) {
		size_t j, k;

		for (j = i;
		     (BASE_TABLE(dfa)[j] & MATCH_FLAG_DIFF_ENCODE) &&
		     !(BASE_TABLE(dfa)[j] & MARK_DIFF_ENCODE);
		     j = k) {
			k = DEFAULT_TABLE(dfa)[j];
			if (j == k)
				goto out;
			if (k < j)
				break;		/* already verified */
			BASE_TABLE(dfa)[j] |= MARK_DIFF_ENCODE;
		}
	}
	error = 0;

out:
	return error;
}

/**
 * dfa_free - free a dfa allocated by aa_dfa_unpack
 * @dfa: the dfa to free  (MAYBE NULL)
 *
 * Requires: reference count to dfa == 0
 */
static void dfa_free(struct aa_dfa *dfa)
{
	if (dfa) {
		int i;

		for (i = 0; i < ARRAY_SIZE(dfa->tables); i++) {
			kvfree(dfa->tables[i]);
			dfa->tables[i] = NULL;
		}
		kfree(dfa);
	}
}

/**
 * aa_dfa_free_kref - free aa_dfa by kref (called by aa_put_dfa)
 * @kr: kref callback for freeing of a dfa  (NOT NULL)
 */
void aa_dfa_free_kref(struct kref *kref)
{
	struct aa_dfa *dfa = container_of(kref, struct aa_dfa, count);
	dfa_free(dfa);
}

/**
 * aa_dfa_unpack - unpack the binary tables of a serialized dfa
 * @blob: aligned serialized stream of data to unpack  (NOT NULL)
 * @size: size of data to unpack
 * @flags: flags controlling what type of accept tables are acceptable
 *
 * Unpack a dfa that has been serialized.  To find information on the dfa
 * format look in Documentation/admin-guide/LSM/apparmor.rst
 * Assumes the dfa @blob stream has been aligned on a 8 byte boundary
 *
 * Returns: an unpacked dfa ready for matching or ERR_PTR on failure
 */
struct aa_dfa *aa_dfa_unpack(void *blob, size_t size, int flags)
{
	int hsize;
	int error = -ENOMEM;
	char *data = blob;
	struct table_header *table = NULL;
	struct aa_dfa *dfa = kzalloc(sizeof(struct aa_dfa), GFP_KERNEL);
	if (!dfa)
		goto fail;

	kref_init(&dfa->count);

	error = -EPROTO;

	/* get dfa table set header */
	if (size < sizeof(struct table_set_header))
		goto fail;

	if (ntohl(*(__be32 *) data) != YYTH_MAGIC)
		goto fail;

	hsize = ntohl(*(__be32 *) (data + 4));
	if (size < hsize)
		goto fail;

	dfa->flags = ntohs(*(__be16 *) (data + 12));
	if (dfa->flags & ~(YYTH_FLAGS))
		goto fail;

	/*
	 * TODO: needed for dfa to support more than 1 oob
	 * if (dfa->flags & YYTH_FLAGS_OOB_TRANS) {
	 *	if (hsize < 16 + 4)
	 *		goto fail;
	 *	dfa->max_oob = ntol(*(__be32 *) (data + 16));
	 *	if (dfa->max <= MAX_OOB_SUPPORTED) {
	 *		pr_err("AppArmor DFA OOB greater than supported\n");
	 *		goto fail;
	 *	}
	 * }
	 */
	dfa->max_oob = 1;

	data += hsize;
	size -= hsize;

	while (size > 0) {
		table = unpack_table(data, size);
		if (!table)
			goto fail;

		switch (table->td_id) {
		case YYTD_ID_ACCEPT:
			if (!(table->td_flags & ACCEPT1_FLAGS(flags)))
				goto fail;
			break;
		case YYTD_ID_ACCEPT2:
			if (!(table->td_flags & ACCEPT2_FLAGS(flags)))
				goto fail;
			break;
		case YYTD_ID_BASE:
			if (table->td_flags != YYTD_DATA32)
				goto fail;
			break;
		case YYTD_ID_DEF:
		case YYTD_ID_NXT:
		case YYTD_ID_CHK:
			if (table->td_flags != YYTD_DATA16)
				goto fail;
			break;
		case YYTD_ID_EC:
			if (table->td_flags != YYTD_DATA8)
				goto fail;
			break;
		default:
			goto fail;
		}
		/* check for duplicate table entry */
		if (dfa->tables[table->td_id])
			goto fail;
		dfa->tables[table->td_id] = table;
		data += table_size(table->td_lolen, table->td_flags);
		size -= table_size(table->td_lolen, table->td_flags);
		table = NULL;
	}
	error = verify_table_headers(dfa->tables, flags);
	if (error)
		goto fail;

	if (flags & DFA_FLAG_VERIFY_STATES) {
		error = verify_dfa(dfa);
		if (error)
			goto fail;
	}

	return dfa;

fail:
	kvfree(table);
	dfa_free(dfa);
	return ERR_PTR(error);
}

#define match_char(state, def, base, next, check, C)	\
do {							\
	u32 b = (base)[(state)];			\
	unsigned int pos = base_idx(b) + (C);		\
	if ((check)[pos] != (state)) {			\
		(state) = (def)[(state)];		\
		if (b & MATCH_FLAG_DIFF_ENCODE)		\
			continue;			\
		break;					\
	}						\
	(state) = (next)[pos];				\
	break;						\
} while (1)

/**
 * aa_dfa_match_len - traverse @dfa to find state @str stops at
 * @dfa: the dfa to match @str against  (NOT NULL)
 * @start: the state of the dfa to start matching in
 * @str: the string of bytes to match against the dfa  (NOT NULL)
 * @len: length of the string of bytes to match
 *
 * aa_dfa_match_len will match @str against the dfa and return the state it
 * finished matching in. The final state can be used to look up the accepting
 * label, or as the start state of a continuing match.
 *
 * This function will happily match again the 0 byte and only finishes
 * when @len input is consumed.
 *
 * Returns: final state reached after input is consumed
 */
unsigned int aa_dfa_match_len(struct aa_dfa *dfa, unsigned int start,
			      const char *str, int len)
{
	u16 *def = DEFAULT_TABLE(dfa);
	u32 *base = BASE_TABLE(dfa);
	u16 *next = NEXT_TABLE(dfa);
	u16 *check = CHECK_TABLE(dfa);
	unsigned int state = start;

	if (state == 0)
		return 0;

	/* current state is <state>, matching character *str */
	if (dfa->tables[YYTD_ID_EC]) {
		/* Equivalence class table defined */
		u8 *equiv = EQUIV_TABLE(dfa);
		for (; len; len--)
			match_char(state, def, base, next, check,
				   equiv[(u8) *str++]);
	} else {
		/* default is direct to next state */
		for (; len; len--)
			match_char(state, def, base, next, check, (u8) *str++);
	}

	return state;
}

/**
 * aa_dfa_match - traverse @dfa to find state @str stops at
 * @dfa: the dfa to match @str against  (NOT NULL)
 * @start: the state of the dfa to start matching in
 * @str: the null terminated string of bytes to match against the dfa (NOT NULL)
 *
 * aa_dfa_match will match @str against the dfa and return the state it
 * finished matching in. The final state can be used to look up the accepting
 * label, or as the start state of a continuing match.
 *
 * Returns: final state reached after input is consumed
 */
unsigned int aa_dfa_match(struct aa_dfa *dfa, unsigned int start,
			  const char *str)
{
	u16 *def = DEFAULT_TABLE(dfa);
	u32 *base = BASE_TABLE(dfa);
	u16 *next = NEXT_TABLE(dfa);
	u16 *check = CHECK_TABLE(dfa);
	unsigned int state = start;

	if (state == 0)
		return 0;

	/* current state is <state>, matching character *str */
	if (dfa->tables[YYTD_ID_EC]) {
		/* Equivalence class table defined */
		u8 *equiv = EQUIV_TABLE(dfa);
		/* default is direct to next state */
		while (*str)
			match_char(state, def, base, next, check,
				   equiv[(u8) *str++]);
	} else {
		/* default is direct to next state */
		while (*str)
			match_char(state, def, base, next, check, (u8) *str++);
	}

	return state;
}

/**
 * aa_dfa_next - step one character to the next state in the dfa
 * @dfa: the dfa to traverse (NOT NULL)
 * @state: the state to start in
 * @c: the input character to transition on
 *
 * aa_dfa_match will step through the dfa by one input character @c
 *
 * Returns: state reach after input @c
 */
unsigned int aa_dfa_next(struct aa_dfa *dfa, unsigned int state,
			  const char c)
{
	u16 *def = DEFAULT_TABLE(dfa);
	u32 *base = BASE_TABLE(dfa);
	u16 *next = NEXT_TABLE(dfa);
	u16 *check = CHECK_TABLE(dfa);

	/* current state is <state>, matching character *str */
	if (dfa->tables[YYTD_ID_EC]) {
		/* Equivalence class table defined */
		u8 *equiv = EQUIV_TABLE(dfa);
		match_char(state, def, base, next, check, equiv[(u8) c]);
	} else
		match_char(state, def, base, next, check, (u8) c);

	return state;
}

unsigned int aa_dfa_outofband_transition(struct aa_dfa *dfa, unsigned int state)
{
	u16 *def = DEFAULT_TABLE(dfa);
	u32 *base = BASE_TABLE(dfa);
	u16 *next = NEXT_TABLE(dfa);
	u16 *check = CHECK_TABLE(dfa);
	u32 b = (base)[(state)];

	if (!(b & MATCH_FLAG_OOB_TRANSITION))
		return DFA_NOMATCH;

	/* No Equivalence class remapping for outofband transitions */
	match_char(state, def, base, next, check, -1);

	return state;
}

/**
 * aa_dfa_match_until - traverse @dfa until accept state or end of input
 * @dfa: the dfa to match @str against  (NOT NULL)
 * @start: the state of the dfa to start matching in
 * @str: the null terminated string of bytes to match against the dfa (NOT NULL)
 * @retpos: first character in str after match OR end of string
 *
 * aa_dfa_match will match @str against the dfa and return the state it
 * finished matching in. The final state can be used to look up the accepting
 * label, or as the start state of a continuing match.
 *
 * Returns: final state reached after input is consumed
 */
unsigned int aa_dfa_match_until(struct aa_dfa *dfa, unsigned int start,
				const char *str, const char **retpos)
{
	u16 *def = DEFAULT_TABLE(dfa);
	u32 *base = BASE_TABLE(dfa);
	u16 *next = NEXT_TABLE(dfa);
	u16 *check = CHECK_TABLE(dfa);
	u32 *accept = ACCEPT_TABLE(dfa);
	unsigned int state = start, pos;

	if (state == 0)
		return 0;

	/* current state is <state>, matching character *str */
	if (dfa->tables[YYTD_ID_EC]) {
		/* Equivalence class table defined */
		u8 *equiv = EQUIV_TABLE(dfa);
		/* default is direct to next state */
		while (*str) {
			pos = base_idx(base[state]) + equiv[(u8) *str++];
			if (check[pos] == state)
				state = next[pos];
			else
				state = def[state];
			if (accept[state])
				break;
		}
	} else {
		/* default is direct to next state */
		while (*str) {
			pos = base_idx(base[state]) + (u8) *str++;
			if (check[pos] == state)
				state = next[pos];
			else
				state = def[state];
			if (accept[state])
				break;
		}
	}

	*retpos = str;
	return state;
}

/**
 * aa_dfa_matchn_until - traverse @dfa until accept or @n bytes consumed
 * @dfa: the dfa to match @str against  (NOT NULL)
 * @start: the state of the dfa to start matching in
 * @str: the string of bytes to match against the dfa  (NOT NULL)
 * @n: length of the string of bytes to match
 * @retpos: first character in str after match OR str + n
 *
 * aa_dfa_match_len will match @str against the dfa and return the state it
 * finished matching in. The final state can be used to look up the accepting
 * label, or as the start state of a continuing match.
 *
 * This function will happily match again the 0 byte and only finishes
 * when @n input is consumed.
 *
 * Returns: final state reached after input is consumed
 */
unsigned int aa_dfa_matchn_until(struct aa_dfa *dfa, unsigned int start,
				 const char *str, int n, const char **retpos)
{
	u16 *def = DEFAULT_TABLE(dfa);
	u32 *base = BASE_TABLE(dfa);
	u16 *next = NEXT_TABLE(dfa);
	u16 *check = CHECK_TABLE(dfa);
	u32 *accept = ACCEPT_TABLE(dfa);
	unsigned int state = start, pos;

	*retpos = NULL;
	if (state == 0)
		return 0;

	/* current state is <state>, matching character *str */
	if (dfa->tables[YYTD_ID_EC]) {
		/* Equivalence class table defined */
		u8 *equiv = EQUIV_TABLE(dfa);
		/* default is direct to next state */
		for (; n; n--) {
			pos = base_idx(base[state]) + equiv[(u8) *str++];
			if (check[pos] == state)
				state = next[pos];
			else
				state = def[state];
			if (accept[state])
				break;
		}
	} else {
		/* default is direct to next state */
		for (; n; n--) {
			pos = base_idx(base[state]) + (u8) *str++;
			if (check[pos] == state)
				state = next[pos];
			else
				state = def[state];
			if (accept[state])
				break;
		}
	}

	*retpos = str;
	return state;
}

#define inc_wb_pos(wb)						\
do {								\
	wb->pos = (wb->pos + 1) & (WB_HISTORY_SIZE - 1);		\
	wb->len = (wb->len + 1) & (WB_HISTORY_SIZE - 1);		\
} while (0)

/* For DFAs that don't support extended tagging of states */
static bool is_loop(struct match_workbuf *wb, unsigned int state,
		    unsigned int *adjust)
{
	unsigned int pos = wb->pos;
	unsigned int i;

	if (wb->history[pos] < state)
		return false;

	for (i = 0; i <= wb->len; i++) {
		if (wb->history[pos] == state) {
			*adjust = i;
			return true;
		}
		if (pos == 0)
			pos = WB_HISTORY_SIZE;
		pos--;
	}

	*adjust = i;
	return true;
}

static unsigned int leftmatch_fb(struct aa_dfa *dfa, unsigned int start,
				 const char *str, struct match_workbuf *wb,
				 unsigned int *count)
{
	u16 *def = DEFAULT_TABLE(dfa);
	u32 *base = BASE_TABLE(dfa);
	u16 *next = NEXT_TABLE(dfa);
	u16 *check = CHECK_TABLE(dfa);
	unsigned int state = start, pos;

	AA_BUG(!dfa);
	AA_BUG(!str);
	AA_BUG(!wb);
	AA_BUG(!count);

	*count = 0;
	if (state == 0)
		return 0;

	/* current state is <state>, matching character *str */
	if (dfa->tables[YYTD_ID_EC]) {
		/* Equivalence class table defined */
		u8 *equiv = EQUIV_TABLE(dfa);
		/* default is direct to next state */
		while (*str) {
			unsigned int adjust;

			wb->history[wb->pos] = state;
			pos = base_idx(base[state]) + equiv[(u8) *str++];
			if (check[pos] == state)
				state = next[pos];
			else
				state = def[state];
			if (is_loop(wb, state, &adjust)) {
				state = aa_dfa_match(dfa, state, str);
				*count -= adjust;
				goto out;
			}
			inc_wb_pos(wb);
			(*count)++;
		}
	} else {
		/* default is direct to next state */
		while (*str) {
			unsigned int adjust;

			wb->history[wb->pos] = state;
			pos = base_idx(base[state]) + (u8) *str++;
			if (check[pos] == state)
				state = next[pos];
			else
				state = def[state];
			if (is_loop(wb, state, &adjust)) {
				state = aa_dfa_match(dfa, state, str);
				*count -= adjust;
				goto out;
			}
			inc_wb_pos(wb);
			(*count)++;
		}
	}

out:
	if (!state)
		*count = 0;
	return state;
}

/**
 * aa_dfa_leftmatch - traverse @dfa to find state @str stops at
 * @dfa: the dfa to match @str against  (NOT NULL)
 * @start: the state of the dfa to start matching in
 * @str: the null terminated string of bytes to match against the dfa (NOT NULL)
 * @count: current count of longest left.
 *
 * aa_dfa_match will match @str against the dfa and return the state it
 * finished matching in. The final state can be used to look up the accepting
 * label, or as the start state of a continuing match.
 *
 * Returns: final state reached after input is consumed
 */
unsigned int aa_dfa_leftmatch(struct aa_dfa *dfa, unsigned int start,
			      const char *str, unsigned int *count)
{
	DEFINE_MATCH_WB(wb);

	/* TODO: match for extended state dfas */

	return leftmatch_fb(dfa, start, str, &wb, count);
}