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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 2009-2010 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 /**
27  * unpack_table - unpack a dfa table (one of accept, default, base, next check)
28  * @blob: data to unpack (NOT NULL)
29  * @bsize: size of blob
30  *
31  * Returns: pointer to table else NULL on failure
32  *
33  * NOTE: must be freed by kvfree (not kmalloc)
34  */
unpack_table(char * blob,size_t bsize)35 static struct table_header *unpack_table(char *blob, size_t bsize)
36 {
37 	struct table_header *table = NULL;
38 	struct table_header th;
39 	size_t tsize;
40 
41 	if (bsize < sizeof(struct table_header))
42 		goto out;
43 
44 	/* loaded td_id's start at 1, subtract 1 now to avoid doing
45 	 * it every time we use td_id as an index
46 	 */
47 	th.td_id = be16_to_cpu(*(u16 *) (blob)) - 1;
48 	th.td_flags = be16_to_cpu(*(u16 *) (blob + 2));
49 	th.td_lolen = be32_to_cpu(*(u32 *) (blob + 8));
50 	blob += sizeof(struct table_header);
51 
52 	if (!(th.td_flags == YYTD_DATA16 || th.td_flags == YYTD_DATA32 ||
53 	      th.td_flags == YYTD_DATA8))
54 		goto out;
55 
56 	tsize = table_size(th.td_lolen, th.td_flags);
57 	if (bsize < tsize)
58 		goto out;
59 
60 	table = kvmalloc(tsize);
61 	if (table) {
62 		*table = th;
63 		if (th.td_flags == YYTD_DATA8)
64 			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
65 				     u8, byte_to_byte);
66 		else if (th.td_flags == YYTD_DATA16)
67 			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
68 				     u16, be16_to_cpu);
69 		else if (th.td_flags == YYTD_DATA32)
70 			UNPACK_ARRAY(table->td_data, blob, th.td_lolen,
71 				     u32, be32_to_cpu);
72 		else
73 			goto fail;
74 	}
75 
76 out:
77 	/* if table was vmalloced make sure the page tables are synced
78 	 * before it is used, as it goes live to all cpus.
79 	 */
80 	if (is_vmalloc_addr(table))
81 		vm_unmap_aliases();
82 	return table;
83 fail:
84 	kvfree(table);
85 	return NULL;
86 }
87 
88 /**
89  * verify_dfa - verify that transitions and states in the tables are in bounds.
90  * @dfa: dfa to test  (NOT NULL)
91  * @flags: flags controlling what type of accept table are acceptable
92  *
93  * Assumes dfa has gone through the first pass verification done by unpacking
94  * NOTE: this does not valid accept table values
95  *
96  * Returns: %0 else error code on failure to verify
97  */
verify_dfa(struct aa_dfa * dfa,int flags)98 static int verify_dfa(struct aa_dfa *dfa, int flags)
99 {
100 	size_t i, state_count, trans_count;
101 	int error = -EPROTO;
102 
103 	/* check that required tables exist */
104 	if (!(dfa->tables[YYTD_ID_DEF] &&
105 	      dfa->tables[YYTD_ID_BASE] &&
106 	      dfa->tables[YYTD_ID_NXT] && dfa->tables[YYTD_ID_CHK]))
107 		goto out;
108 
109 	/* accept.size == default.size == base.size */
110 	state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
111 	if (ACCEPT1_FLAGS(flags)) {
112 		if (!dfa->tables[YYTD_ID_ACCEPT])
113 			goto out;
114 		if (state_count != dfa->tables[YYTD_ID_ACCEPT]->td_lolen)
115 			goto out;
116 	}
117 	if (ACCEPT2_FLAGS(flags)) {
118 		if (!dfa->tables[YYTD_ID_ACCEPT2])
119 			goto out;
120 		if (state_count != dfa->tables[YYTD_ID_ACCEPT2]->td_lolen)
121 			goto out;
122 	}
123 	if (state_count != dfa->tables[YYTD_ID_DEF]->td_lolen)
124 		goto out;
125 
126 	/* next.size == chk.size */
127 	trans_count = dfa->tables[YYTD_ID_NXT]->td_lolen;
128 	if (trans_count != dfa->tables[YYTD_ID_CHK]->td_lolen)
129 		goto out;
130 
131 	/* if equivalence classes then its table size must be 256 */
132 	if (dfa->tables[YYTD_ID_EC] &&
133 	    dfa->tables[YYTD_ID_EC]->td_lolen != 256)
134 		goto out;
135 
136 	if (flags & DFA_FLAG_VERIFY_STATES) {
137 		for (i = 0; i < state_count; i++) {
138 			if (DEFAULT_TABLE(dfa)[i] >= state_count)
139 				goto out;
140 			/* TODO: do check that DEF state recursion terminates */
141 			if (BASE_TABLE(dfa)[i] + 255 >= trans_count) {
142 				printk(KERN_ERR "AppArmor DFA next/check upper "
143 				       "bounds error\n");
144 				goto out;
145 			}
146 		}
147 
148 		for (i = 0; i < trans_count; i++) {
149 			if (NEXT_TABLE(dfa)[i] >= state_count)
150 				goto out;
151 			if (CHECK_TABLE(dfa)[i] >= state_count)
152 				goto out;
153 		}
154 	}
155 
156 	error = 0;
157 out:
158 	return error;
159 }
160 
161 /**
162  * dfa_free - free a dfa allocated by aa_dfa_unpack
163  * @dfa: the dfa to free  (MAYBE NULL)
164  *
165  * Requires: reference count to dfa == 0
166  */
dfa_free(struct aa_dfa * dfa)167 static void dfa_free(struct aa_dfa *dfa)
168 {
169 	if (dfa) {
170 		int i;
171 
172 		for (i = 0; i < ARRAY_SIZE(dfa->tables); i++) {
173 			kvfree(dfa->tables[i]);
174 			dfa->tables[i] = NULL;
175 		}
176 		kfree(dfa);
177 	}
178 }
179 
180 /**
181  * aa_dfa_free_kref - free aa_dfa by kref (called by aa_put_dfa)
182  * @kr: kref callback for freeing of a dfa  (NOT NULL)
183  */
aa_dfa_free_kref(struct kref * kref)184 void aa_dfa_free_kref(struct kref *kref)
185 {
186 	struct aa_dfa *dfa = container_of(kref, struct aa_dfa, count);
187 	dfa_free(dfa);
188 }
189 
190 /**
191  * aa_dfa_unpack - unpack the binary tables of a serialized dfa
192  * @blob: aligned serialized stream of data to unpack  (NOT NULL)
193  * @size: size of data to unpack
194  * @flags: flags controlling what type of accept tables are acceptable
195  *
196  * Unpack a dfa that has been serialized.  To find information on the dfa
197  * format look in Documentation/security/apparmor.txt
198  * Assumes the dfa @blob stream has been aligned on a 8 byte boundary
199  *
200  * Returns: an unpacked dfa ready for matching or ERR_PTR on failure
201  */
aa_dfa_unpack(void * blob,size_t size,int flags)202 struct aa_dfa *aa_dfa_unpack(void *blob, size_t size, int flags)
203 {
204 	int hsize;
205 	int error = -ENOMEM;
206 	char *data = blob;
207 	struct table_header *table = NULL;
208 	struct aa_dfa *dfa = kzalloc(sizeof(struct aa_dfa), GFP_KERNEL);
209 	if (!dfa)
210 		goto fail;
211 
212 	kref_init(&dfa->count);
213 
214 	error = -EPROTO;
215 
216 	/* get dfa table set header */
217 	if (size < sizeof(struct table_set_header))
218 		goto fail;
219 
220 	if (ntohl(*(u32 *) data) != YYTH_MAGIC)
221 		goto fail;
222 
223 	hsize = ntohl(*(u32 *) (data + 4));
224 	if (size < hsize)
225 		goto fail;
226 
227 	dfa->flags = ntohs(*(u16 *) (data + 12));
228 	data += hsize;
229 	size -= hsize;
230 
231 	while (size > 0) {
232 		table = unpack_table(data, size);
233 		if (!table)
234 			goto fail;
235 
236 		switch (table->td_id) {
237 		case YYTD_ID_ACCEPT:
238 			if (!(table->td_flags & ACCEPT1_FLAGS(flags)))
239 				goto fail;
240 			break;
241 		case YYTD_ID_ACCEPT2:
242 			if (!(table->td_flags & ACCEPT2_FLAGS(flags)))
243 				goto fail;
244 			break;
245 		case YYTD_ID_BASE:
246 			if (table->td_flags != YYTD_DATA32)
247 				goto fail;
248 			break;
249 		case YYTD_ID_DEF:
250 		case YYTD_ID_NXT:
251 		case YYTD_ID_CHK:
252 			if (table->td_flags != YYTD_DATA16)
253 				goto fail;
254 			break;
255 		case YYTD_ID_EC:
256 			if (table->td_flags != YYTD_DATA8)
257 				goto fail;
258 			break;
259 		default:
260 			goto fail;
261 		}
262 		/* check for duplicate table entry */
263 		if (dfa->tables[table->td_id])
264 			goto fail;
265 		dfa->tables[table->td_id] = table;
266 		data += table_size(table->td_lolen, table->td_flags);
267 		size -= table_size(table->td_lolen, table->td_flags);
268 		table = NULL;
269 	}
270 
271 	error = verify_dfa(dfa, flags);
272 	if (error)
273 		goto fail;
274 
275 	return dfa;
276 
277 fail:
278 	kvfree(table);
279 	dfa_free(dfa);
280 	return ERR_PTR(error);
281 }
282 
283 /**
284  * aa_dfa_match_len - traverse @dfa to find state @str stops at
285  * @dfa: the dfa to match @str against  (NOT NULL)
286  * @start: the state of the dfa to start matching in
287  * @str: the string of bytes to match against the dfa  (NOT NULL)
288  * @len: length of the string of bytes to match
289  *
290  * aa_dfa_match_len will match @str against the dfa and return the state it
291  * finished matching in. The final state can be used to look up the accepting
292  * label, or as the start state of a continuing match.
293  *
294  * This function will happily match again the 0 byte and only finishes
295  * when @len input is consumed.
296  *
297  * Returns: final state reached after input is consumed
298  */
aa_dfa_match_len(struct aa_dfa * dfa,unsigned int start,const char * str,int len)299 unsigned int aa_dfa_match_len(struct aa_dfa *dfa, unsigned int start,
300 			      const char *str, int len)
301 {
302 	u16 *def = DEFAULT_TABLE(dfa);
303 	u32 *base = BASE_TABLE(dfa);
304 	u16 *next = NEXT_TABLE(dfa);
305 	u16 *check = CHECK_TABLE(dfa);
306 	unsigned int state = start, pos;
307 
308 	if (state == 0)
309 		return 0;
310 
311 	/* current state is <state>, matching character *str */
312 	if (dfa->tables[YYTD_ID_EC]) {
313 		/* Equivalence class table defined */
314 		u8 *equiv = EQUIV_TABLE(dfa);
315 		/* default is direct to next state */
316 		for (; len; len--) {
317 			pos = base[state] + equiv[(u8) *str++];
318 			if (check[pos] == state)
319 				state = next[pos];
320 			else
321 				state = def[state];
322 		}
323 	} else {
324 		/* default is direct to next state */
325 		for (; len; len--) {
326 			pos = base[state] + (u8) *str++;
327 			if (check[pos] == state)
328 				state = next[pos];
329 			else
330 				state = def[state];
331 		}
332 	}
333 
334 	return state;
335 }
336 
337 /**
338  * aa_dfa_match - traverse @dfa to find state @str stops at
339  * @dfa: the dfa to match @str against  (NOT NULL)
340  * @start: the state of the dfa to start matching in
341  * @str: the null terminated string of bytes to match against the dfa (NOT NULL)
342  *
343  * aa_dfa_match will match @str against the dfa and return the state it
344  * finished matching in. The final state can be used to look up the accepting
345  * label, or as the start state of a continuing match.
346  *
347  * Returns: final state reached after input is consumed
348  */
aa_dfa_match(struct aa_dfa * dfa,unsigned int start,const char * str)349 unsigned int aa_dfa_match(struct aa_dfa *dfa, unsigned int start,
350 			  const char *str)
351 {
352 	u16 *def = DEFAULT_TABLE(dfa);
353 	u32 *base = BASE_TABLE(dfa);
354 	u16 *next = NEXT_TABLE(dfa);
355 	u16 *check = CHECK_TABLE(dfa);
356 	unsigned int state = start, pos;
357 
358 	if (state == 0)
359 		return 0;
360 
361 	/* current state is <state>, matching character *str */
362 	if (dfa->tables[YYTD_ID_EC]) {
363 		/* Equivalence class table defined */
364 		u8 *equiv = EQUIV_TABLE(dfa);
365 		/* default is direct to next state */
366 		while (*str) {
367 			pos = base[state] + equiv[(u8) *str++];
368 			if (check[pos] == state)
369 				state = next[pos];
370 			else
371 				state = def[state];
372 		}
373 	} else {
374 		/* default is direct to next state */
375 		while (*str) {
376 			pos = base[state] + (u8) *str++;
377 			if (check[pos] == state)
378 				state = next[pos];
379 			else
380 				state = def[state];
381 		}
382 	}
383 
384 	return state;
385 }
386 
387 /**
388  * aa_dfa_next - step one character to the next state in the dfa
389  * @dfa: the dfa to tranverse (NOT NULL)
390  * @state: the state to start in
391  * @c: the input character to transition on
392  *
393  * aa_dfa_match will step through the dfa by one input character @c
394  *
395  * Returns: state reach after input @c
396  */
aa_dfa_next(struct aa_dfa * dfa,unsigned int state,const char c)397 unsigned int aa_dfa_next(struct aa_dfa *dfa, unsigned int state,
398 			  const char c)
399 {
400 	u16 *def = DEFAULT_TABLE(dfa);
401 	u32 *base = BASE_TABLE(dfa);
402 	u16 *next = NEXT_TABLE(dfa);
403 	u16 *check = CHECK_TABLE(dfa);
404 	unsigned int pos;
405 
406 	/* current state is <state>, matching character *str */
407 	if (dfa->tables[YYTD_ID_EC]) {
408 		/* Equivalence class table defined */
409 		u8 *equiv = EQUIV_TABLE(dfa);
410 		/* default is direct to next state */
411 
412 		pos = base[state] + equiv[(u8) c];
413 		if (check[pos] == state)
414 			state = next[pos];
415 		else
416 			state = def[state];
417 	} else {
418 		/* default is direct to next state */
419 		pos = base[state] + (u8) c;
420 		if (check[pos] == state)
421 			state = next[pos];
422 		else
423 			state = def[state];
424 	}
425 
426 	return state;
427 }
428