1/*
2 * AppArmor security module
3 *
4 * This file contains AppArmor dfa based regular expression matching engine
5 *
6 * Copyright (C) 1998-2008 Novell/SUSE
7 * Copyright 2009-2012 Canonical Ltd.
8 *
9 * This program is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU General Public License as
11 * published by the Free Software Foundation, version 2 of the
12 * License.
13 */
14
15#include <linux/errno.h>
16#include <linux/kernel.h>
17#include <linux/mm.h>
18#include <linux/slab.h>
19#include <linux/vmalloc.h>
20#include <linux/err.h>
21#include <linux/kref.h>
22
23#include "include/apparmor.h"
24#include "include/match.h"
25
26#define base_idx(X) ((X) & 0xffffff)
27
28/**
29 * unpack_table - unpack a dfa table (one of accept, default, base, next check)
30 * @blob: data to unpack (NOT NULL)
31 * @bsize: size of blob
32 *
33 * Returns: pointer to table else NULL on failure
34 *
35 * NOTE: must be freed by kvfree (not kfree)
36 */
37static struct table_header *unpack_table(char *blob, size_t bsize)
38{
39	struct table_header *table = NULL;
40	struct table_header th;
41	size_t tsize;
42
43	if (bsize < sizeof(struct table_header))
44		goto out;
45
46	/* loaded td_id's start at 1, subtract 1 now to avoid doing
47	 * it every time we use td_id as an index
48	 */
49	th.td_id = be16_to_cpu(*(u16 *) (blob)) - 1;
50	th.td_flags = be16_to_cpu(*(u16 *) (blob + 2));
51	th.td_lolen = be32_to_cpu(*(u32 *) (blob + 8));
52	blob += sizeof(struct table_header);
53
54	if (!(th.td_flags == YYTD_DATA16 || th.td_flags == YYTD_DATA32 ||
55	      th.td_flags == YYTD_DATA8))
56		goto out;
57
58	tsize = table_size(th.td_lolen, th.td_flags);
59	if (bsize < tsize)
60		goto out;
61
62	table = kvzalloc(tsize);
63	if (table) {
64		*table = th;
65		if (th.td_flags == YYTD_DATA8)
66			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
67				     u8, byte_to_byte);
68		else if (th.td_flags == YYTD_DATA16)
69			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
70				     u16, be16_to_cpu);
71		else if (th.td_flags == YYTD_DATA32)
72			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
73				     u32, be32_to_cpu);
74		else
75			goto fail;
76	}
77
78out:
79	/* if table was vmalloced make sure the page tables are synced
80	 * before it is used, as it goes live to all cpus.
81	 */
82	if (is_vmalloc_addr(table))
83		vm_unmap_aliases();
84	return table;
85fail:
86	kvfree(table);
87	return NULL;
88}
89
90/**
91 * verify_dfa - verify that transitions and states in the tables are in bounds.
92 * @dfa: dfa to test  (NOT NULL)
93 * @flags: flags controlling what type of accept table are acceptable
94 *
95 * Assumes dfa has gone through the first pass verification done by unpacking
96 * NOTE: this does not valid accept table values
97 *
98 * Returns: %0 else error code on failure to verify
99 */
100static int verify_dfa(struct aa_dfa *dfa, int flags)
101{
102	size_t i, state_count, trans_count;
103	int error = -EPROTO;
104
105	/* check that required tables exist */
106	if (!(dfa->tables[YYTD_ID_DEF] &&
107	      dfa->tables[YYTD_ID_BASE] &&
108	      dfa->tables[YYTD_ID_NXT] && dfa->tables[YYTD_ID_CHK]))
109		goto out;
110
111	/* accept.size == default.size == base.size */
112	state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
113	if (ACCEPT1_FLAGS(flags)) {
114		if (!dfa->tables[YYTD_ID_ACCEPT])
115			goto out;
116		if (state_count != dfa->tables[YYTD_ID_ACCEPT]->td_lolen)
117			goto out;
118	}
119	if (ACCEPT2_FLAGS(flags)) {
120		if (!dfa->tables[YYTD_ID_ACCEPT2])
121			goto out;
122		if (state_count != dfa->tables[YYTD_ID_ACCEPT2]->td_lolen)
123			goto out;
124	}
125	if (state_count != dfa->tables[YYTD_ID_DEF]->td_lolen)
126		goto out;
127
128	/* next.size == chk.size */
129	trans_count = dfa->tables[YYTD_ID_NXT]->td_lolen;
130	if (trans_count != dfa->tables[YYTD_ID_CHK]->td_lolen)
131		goto out;
132
133	/* if equivalence classes then its table size must be 256 */
134	if (dfa->tables[YYTD_ID_EC] &&
135	    dfa->tables[YYTD_ID_EC]->td_lolen != 256)
136		goto out;
137
138	if (flags & DFA_FLAG_VERIFY_STATES) {
139		for (i = 0; i < state_count; i++) {
140			if (DEFAULT_TABLE(dfa)[i] >= state_count)
141				goto out;
142			if (base_idx(BASE_TABLE(dfa)[i]) + 255 >= trans_count) {
143				printk(KERN_ERR "AppArmor DFA next/check upper "
144				       "bounds error\n");
145				goto out;
146			}
147		}
148
149		for (i = 0; i < trans_count; i++) {
150			if (NEXT_TABLE(dfa)[i] >= state_count)
151				goto out;
152			if (CHECK_TABLE(dfa)[i] >= state_count)
153				goto out;
154		}
155	}
156
157	error = 0;
158out:
159	return error;
160}
161
162/**
163 * dfa_free - free a dfa allocated by aa_dfa_unpack
164 * @dfa: the dfa to free  (MAYBE NULL)
165 *
166 * Requires: reference count to dfa == 0
167 */
168static void dfa_free(struct aa_dfa *dfa)
169{
170	if (dfa) {
171		int i;
172
173		for (i = 0; i < ARRAY_SIZE(dfa->tables); i++) {
174			kvfree(dfa->tables[i]);
175			dfa->tables[i] = NULL;
176		}
177		kfree(dfa);
178	}
179}
180
181/**
182 * aa_dfa_free_kref - free aa_dfa by kref (called by aa_put_dfa)
183 * @kr: kref callback for freeing of a dfa  (NOT NULL)
184 */
185void aa_dfa_free_kref(struct kref *kref)
186{
187	struct aa_dfa *dfa = container_of(kref, struct aa_dfa, count);
188	dfa_free(dfa);
189}
190
191/**
192 * aa_dfa_unpack - unpack the binary tables of a serialized dfa
193 * @blob: aligned serialized stream of data to unpack  (NOT NULL)
194 * @size: size of data to unpack
195 * @flags: flags controlling what type of accept tables are acceptable
196 *
197 * Unpack a dfa that has been serialized.  To find information on the dfa
198 * format look in Documentation/security/apparmor.txt
199 * Assumes the dfa @blob stream has been aligned on a 8 byte boundary
200 *
201 * Returns: an unpacked dfa ready for matching or ERR_PTR on failure
202 */
203struct aa_dfa *aa_dfa_unpack(void *blob, size_t size, int flags)
204{
205	int hsize;
206	int error = -ENOMEM;
207	char *data = blob;
208	struct table_header *table = NULL;
209	struct aa_dfa *dfa = kzalloc(sizeof(struct aa_dfa), GFP_KERNEL);
210	if (!dfa)
211		goto fail;
212
213	kref_init(&dfa->count);
214
215	error = -EPROTO;
216
217	/* get dfa table set header */
218	if (size < sizeof(struct table_set_header))
219		goto fail;
220
221	if (ntohl(*(u32 *) data) != YYTH_MAGIC)
222		goto fail;
223
224	hsize = ntohl(*(u32 *) (data + 4));
225	if (size < hsize)
226		goto fail;
227
228	dfa->flags = ntohs(*(u16 *) (data + 12));
229	data += hsize;
230	size -= hsize;
231
232	while (size > 0) {
233		table = unpack_table(data, size);
234		if (!table)
235			goto fail;
236
237		switch (table->td_id) {
238		case YYTD_ID_ACCEPT:
239			if (!(table->td_flags & ACCEPT1_FLAGS(flags)))
240				goto fail;
241			break;
242		case YYTD_ID_ACCEPT2:
243			if (!(table->td_flags & ACCEPT2_FLAGS(flags)))
244				goto fail;
245			break;
246		case YYTD_ID_BASE:
247			if (table->td_flags != YYTD_DATA32)
248				goto fail;
249			break;
250		case YYTD_ID_DEF:
251		case YYTD_ID_NXT:
252		case YYTD_ID_CHK:
253			if (table->td_flags != YYTD_DATA16)
254				goto fail;
255			break;
256		case YYTD_ID_EC:
257			if (table->td_flags != YYTD_DATA8)
258				goto fail;
259			break;
260		default:
261			goto fail;
262		}
263		/* check for duplicate table entry */
264		if (dfa->tables[table->td_id])
265			goto fail;
266		dfa->tables[table->td_id] = table;
267		data += table_size(table->td_lolen, table->td_flags);
268		size -= table_size(table->td_lolen, table->td_flags);
269		table = NULL;
270	}
271
272	error = verify_dfa(dfa, flags);
273	if (error)
274		goto fail;
275
276	return dfa;
277
278fail:
279	kvfree(table);
280	dfa_free(dfa);
281	return ERR_PTR(error);
282}
283
284/**
285 * aa_dfa_match_len - traverse @dfa to find state @str stops at
286 * @dfa: the dfa to match @str against  (NOT NULL)
287 * @start: the state of the dfa to start matching in
288 * @str: the string of bytes to match against the dfa  (NOT NULL)
289 * @len: length of the string of bytes to match
290 *
291 * aa_dfa_match_len will match @str against the dfa and return the state it
292 * finished matching in. The final state can be used to look up the accepting
293 * label, or as the start state of a continuing match.
294 *
295 * This function will happily match again the 0 byte and only finishes
296 * when @len input is consumed.
297 *
298 * Returns: final state reached after input is consumed
299 */
300unsigned int aa_dfa_match_len(struct aa_dfa *dfa, unsigned int start,
301			      const char *str, int len)
302{
303	u16 *def = DEFAULT_TABLE(dfa);
304	u32 *base = BASE_TABLE(dfa);
305	u16 *next = NEXT_TABLE(dfa);
306	u16 *check = CHECK_TABLE(dfa);
307	unsigned int state = start, pos;
308
309	if (state == 0)
310		return 0;
311
312	/* current state is <state>, matching character *str */
313	if (dfa->tables[YYTD_ID_EC]) {
314		/* Equivalence class table defined */
315		u8 *equiv = EQUIV_TABLE(dfa);
316		/* default is direct to next state */
317		for (; len; len--) {
318			pos = base_idx(base[state]) + equiv[(u8) *str++];
319			if (check[pos] == state)
320				state = next[pos];
321			else
322				state = def[state];
323		}
324	} else {
325		/* default is direct to next state */
326		for (; len; len--) {
327			pos = base_idx(base[state]) + (u8) *str++;
328			if (check[pos] == state)
329				state = next[pos];
330			else
331				state = def[state];
332		}
333	}
334
335	return state;
336}
337
338/**
339 * aa_dfa_match - traverse @dfa to find state @str stops at
340 * @dfa: the dfa to match @str against  (NOT NULL)
341 * @start: the state of the dfa to start matching in
342 * @str: the null terminated string of bytes to match against the dfa (NOT NULL)
343 *
344 * aa_dfa_match will match @str against the dfa and return the state it
345 * finished matching in. The final state can be used to look up the accepting
346 * label, or as the start state of a continuing match.
347 *
348 * Returns: final state reached after input is consumed
349 */
350unsigned int aa_dfa_match(struct aa_dfa *dfa, unsigned int start,
351			  const char *str)
352{
353	u16 *def = DEFAULT_TABLE(dfa);
354	u32 *base = BASE_TABLE(dfa);
355	u16 *next = NEXT_TABLE(dfa);
356	u16 *check = CHECK_TABLE(dfa);
357	unsigned int state = start, pos;
358
359	if (state == 0)
360		return 0;
361
362	/* current state is <state>, matching character *str */
363	if (dfa->tables[YYTD_ID_EC]) {
364		/* Equivalence class table defined */
365		u8 *equiv = EQUIV_TABLE(dfa);
366		/* default is direct to next state */
367		while (*str) {
368			pos = base_idx(base[state]) + equiv[(u8) *str++];
369			if (check[pos] == state)
370				state = next[pos];
371			else
372				state = def[state];
373		}
374	} else {
375		/* default is direct to next state */
376		while (*str) {
377			pos = base_idx(base[state]) + (u8) *str++;
378			if (check[pos] == state)
379				state = next[pos];
380			else
381				state = def[state];
382		}
383	}
384
385	return state;
386}
387
388/**
389 * aa_dfa_next - step one character to the next state in the dfa
390 * @dfa: the dfa to tranverse (NOT NULL)
391 * @state: the state to start in
392 * @c: the input character to transition on
393 *
394 * aa_dfa_match will step through the dfa by one input character @c
395 *
396 * Returns: state reach after input @c
397 */
398unsigned int aa_dfa_next(struct aa_dfa *dfa, unsigned int state,
399			  const char c)
400{
401	u16 *def = DEFAULT_TABLE(dfa);
402	u32 *base = BASE_TABLE(dfa);
403	u16 *next = NEXT_TABLE(dfa);
404	u16 *check = CHECK_TABLE(dfa);
405	unsigned int pos;
406
407	/* current state is <state>, matching character *str */
408	if (dfa->tables[YYTD_ID_EC]) {
409		/* Equivalence class table defined */
410		u8 *equiv = EQUIV_TABLE(dfa);
411		/* default is direct to next state */
412
413		pos = base_idx(base[state]) + equiv[(u8) c];
414		if (check[pos] == state)
415			state = next[pos];
416		else
417			state = def[state];
418	} else {
419		/* default is direct to next state */
420		pos = base_idx(base[state]) + (u8) c;
421		if (check[pos] == state)
422			state = next[pos];
423		else
424			state = def[state];
425	}
426
427	return state;
428}
429