1/* Decoder for ASN.1 BER/DER/CER encoded bytestream
2 *
3 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public Licence
8 * as published by the Free Software Foundation; either version
9 * 2 of the Licence, or (at your option) any later version.
10 */
11
12#include <linux/export.h>
13#include <linux/kernel.h>
14#include <linux/errno.h>
15#include <linux/asn1_decoder.h>
16#include <linux/asn1_ber_bytecode.h>
17
18static const unsigned char asn1_op_lengths[ASN1_OP__NR] = {
19	/*					OPC TAG JMP ACT */
20	[ASN1_OP_MATCH]				= 1 + 1,
21	[ASN1_OP_MATCH_OR_SKIP]			= 1 + 1,
22	[ASN1_OP_MATCH_ACT]			= 1 + 1     + 1,
23	[ASN1_OP_MATCH_ACT_OR_SKIP]		= 1 + 1     + 1,
24	[ASN1_OP_MATCH_JUMP]			= 1 + 1 + 1,
25	[ASN1_OP_MATCH_JUMP_OR_SKIP]		= 1 + 1 + 1,
26	[ASN1_OP_MATCH_ANY]			= 1,
27	[ASN1_OP_MATCH_ANY_ACT]			= 1         + 1,
28	[ASN1_OP_COND_MATCH_OR_SKIP]		= 1 + 1,
29	[ASN1_OP_COND_MATCH_ACT_OR_SKIP]	= 1 + 1     + 1,
30	[ASN1_OP_COND_MATCH_JUMP_OR_SKIP]	= 1 + 1 + 1,
31	[ASN1_OP_COND_MATCH_ANY]		= 1,
32	[ASN1_OP_COND_MATCH_ANY_ACT]		= 1         + 1,
33	[ASN1_OP_COND_FAIL]			= 1,
34	[ASN1_OP_COMPLETE]			= 1,
35	[ASN1_OP_ACT]				= 1         + 1,
36	[ASN1_OP_RETURN]			= 1,
37	[ASN1_OP_END_SEQ]			= 1,
38	[ASN1_OP_END_SEQ_OF]			= 1     + 1,
39	[ASN1_OP_END_SET]			= 1,
40	[ASN1_OP_END_SET_OF]			= 1     + 1,
41	[ASN1_OP_END_SEQ_ACT]			= 1         + 1,
42	[ASN1_OP_END_SEQ_OF_ACT]		= 1     + 1 + 1,
43	[ASN1_OP_END_SET_ACT]			= 1         + 1,
44	[ASN1_OP_END_SET_OF_ACT]		= 1     + 1 + 1,
45};
46
47/*
48 * Find the length of an indefinite length object
49 * @data: The data buffer
50 * @datalen: The end of the innermost containing element in the buffer
51 * @_dp: The data parse cursor (updated before returning)
52 * @_len: Where to return the size of the element.
53 * @_errmsg: Where to return a pointer to an error message on error
54 */
55static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen,
56				       size_t *_dp, size_t *_len,
57				       const char **_errmsg)
58{
59	unsigned char tag, tmp;
60	size_t dp = *_dp, len, n;
61	int indef_level = 1;
62
63next_tag:
64	if (unlikely(datalen - dp < 2)) {
65		if (datalen == dp)
66			goto missing_eoc;
67		goto data_overrun_error;
68	}
69
70	/* Extract a tag from the data */
71	tag = data[dp++];
72	if (tag == 0) {
73		/* It appears to be an EOC. */
74		if (data[dp++] != 0)
75			goto invalid_eoc;
76		if (--indef_level <= 0) {
77			*_len = dp - *_dp;
78			*_dp = dp;
79			return 0;
80		}
81		goto next_tag;
82	}
83
84	if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) {
85		do {
86			if (unlikely(datalen - dp < 2))
87				goto data_overrun_error;
88			tmp = data[dp++];
89		} while (tmp & 0x80);
90	}
91
92	/* Extract the length */
93	len = data[dp++];
94	if (len <= 0x7f) {
95		dp += len;
96		goto next_tag;
97	}
98
99	if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
100		/* Indefinite length */
101		if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5))
102			goto indefinite_len_primitive;
103		indef_level++;
104		goto next_tag;
105	}
106
107	n = len - 0x80;
108	if (unlikely(n > sizeof(size_t) - 1))
109		goto length_too_long;
110	if (unlikely(n > datalen - dp))
111		goto data_overrun_error;
112	for (len = 0; n > 0; n--) {
113		len <<= 8;
114		len |= data[dp++];
115	}
116	dp += len;
117	goto next_tag;
118
119length_too_long:
120	*_errmsg = "Unsupported length";
121	goto error;
122indefinite_len_primitive:
123	*_errmsg = "Indefinite len primitive not permitted";
124	goto error;
125invalid_eoc:
126	*_errmsg = "Invalid length EOC";
127	goto error;
128data_overrun_error:
129	*_errmsg = "Data overrun error";
130	goto error;
131missing_eoc:
132	*_errmsg = "Missing EOC in indefinite len cons";
133error:
134	*_dp = dp;
135	return -1;
136}
137
138/**
139 * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern
140 * @decoder: The decoder definition (produced by asn1_compiler)
141 * @context: The caller's context (to be passed to the action functions)
142 * @data: The encoded data
143 * @datalen: The size of the encoded data
144 *
145 * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern
146 * produced by asn1_compiler.  Action functions are called on marked tags to
147 * allow the caller to retrieve significant data.
148 *
149 * LIMITATIONS:
150 *
151 * To keep down the amount of stack used by this function, the following limits
152 * have been imposed:
153 *
154 *  (1) This won't handle datalen > 65535 without increasing the size of the
155 *	cons stack elements and length_too_long checking.
156 *
157 *  (2) The stack of constructed types is 10 deep.  If the depth of non-leaf
158 *	constructed types exceeds this, the decode will fail.
159 *
160 *  (3) The SET type (not the SET OF type) isn't really supported as tracking
161 *	what members of the set have been seen is a pain.
162 */
163int asn1_ber_decoder(const struct asn1_decoder *decoder,
164		     void *context,
165		     const unsigned char *data,
166		     size_t datalen)
167{
168	const unsigned char *machine = decoder->machine;
169	const asn1_action_t *actions = decoder->actions;
170	size_t machlen = decoder->machlen;
171	enum asn1_opcode op;
172	unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0;
173	const char *errmsg;
174	size_t pc = 0, dp = 0, tdp = 0, len = 0;
175	int ret;
176
177	unsigned char flags = 0;
178#define FLAG_INDEFINITE_LENGTH	0x01
179#define FLAG_MATCHED		0x02
180#define FLAG_CONS		0x20 /* Corresponds to CONS bit in the opcode tag
181				      * - ie. whether or not we are going to parse
182				      *   a compound type.
183				      */
184
185#define NR_CONS_STACK 10
186	unsigned short cons_dp_stack[NR_CONS_STACK];
187	unsigned short cons_datalen_stack[NR_CONS_STACK];
188	unsigned char cons_hdrlen_stack[NR_CONS_STACK];
189#define NR_JUMP_STACK 10
190	unsigned char jump_stack[NR_JUMP_STACK];
191
192	if (datalen > 65535)
193		return -EMSGSIZE;
194
195next_op:
196	pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n",
197		 pc, machlen, dp, datalen, csp, jsp);
198	if (unlikely(pc >= machlen))
199		goto machine_overrun_error;
200	op = machine[pc];
201	if (unlikely(pc + asn1_op_lengths[op] > machlen))
202		goto machine_overrun_error;
203
204	/* If this command is meant to match a tag, then do that before
205	 * evaluating the command.
206	 */
207	if (op <= ASN1_OP__MATCHES_TAG) {
208		unsigned char tmp;
209
210		/* Skip conditional matches if possible */
211		if ((op & ASN1_OP_MATCH__COND &&
212		     flags & FLAG_MATCHED) ||
213		    dp == datalen) {
214			pc += asn1_op_lengths[op];
215			goto next_op;
216		}
217
218		flags = 0;
219		hdr = 2;
220
221		/* Extract a tag from the data */
222		if (unlikely(dp >= datalen - 1))
223			goto data_overrun_error;
224		tag = data[dp++];
225		if (unlikely((tag & 0x1f) == ASN1_LONG_TAG))
226			goto long_tag_not_supported;
227
228		if (op & ASN1_OP_MATCH__ANY) {
229			pr_debug("- any %02x\n", tag);
230		} else {
231			/* Extract the tag from the machine
232			 * - Either CONS or PRIM are permitted in the data if
233			 *   CONS is not set in the op stream, otherwise CONS
234			 *   is mandatory.
235			 */
236			optag = machine[pc + 1];
237			flags |= optag & FLAG_CONS;
238
239			/* Determine whether the tag matched */
240			tmp = optag ^ tag;
241			tmp &= ~(optag & ASN1_CONS_BIT);
242			pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp);
243			if (tmp != 0) {
244				/* All odd-numbered tags are MATCH_OR_SKIP. */
245				if (op & ASN1_OP_MATCH__SKIP) {
246					pc += asn1_op_lengths[op];
247					dp--;
248					goto next_op;
249				}
250				goto tag_mismatch;
251			}
252		}
253		flags |= FLAG_MATCHED;
254
255		len = data[dp++];
256		if (len > 0x7f) {
257			if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
258				/* Indefinite length */
259				if (unlikely(!(tag & ASN1_CONS_BIT)))
260					goto indefinite_len_primitive;
261				flags |= FLAG_INDEFINITE_LENGTH;
262				if (unlikely(2 > datalen - dp))
263					goto data_overrun_error;
264			} else {
265				int n = len - 0x80;
266				if (unlikely(n > 2))
267					goto length_too_long;
268				if (unlikely(dp >= datalen - n))
269					goto data_overrun_error;
270				hdr += n;
271				for (len = 0; n > 0; n--) {
272					len <<= 8;
273					len |= data[dp++];
274				}
275				if (unlikely(len > datalen - dp))
276					goto data_overrun_error;
277			}
278		}
279
280		if (flags & FLAG_CONS) {
281			/* For expected compound forms, we stack the positions
282			 * of the start and end of the data.
283			 */
284			if (unlikely(csp >= NR_CONS_STACK))
285				goto cons_stack_overflow;
286			cons_dp_stack[csp] = dp;
287			cons_hdrlen_stack[csp] = hdr;
288			if (!(flags & FLAG_INDEFINITE_LENGTH)) {
289				cons_datalen_stack[csp] = datalen;
290				datalen = dp + len;
291			} else {
292				cons_datalen_stack[csp] = 0;
293			}
294			csp++;
295		}
296
297		pr_debug("- TAG: %02x %zu%s\n",
298			 tag, len, flags & FLAG_CONS ? " CONS" : "");
299		tdp = dp;
300	}
301
302	/* Decide how to handle the operation */
303	switch (op) {
304	case ASN1_OP_MATCH_ANY_ACT:
305	case ASN1_OP_COND_MATCH_ANY_ACT:
306		ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len);
307		if (ret < 0)
308			return ret;
309		goto skip_data;
310
311	case ASN1_OP_MATCH_ACT:
312	case ASN1_OP_MATCH_ACT_OR_SKIP:
313	case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
314		ret = actions[machine[pc + 2]](context, hdr, tag, data + dp, len);
315		if (ret < 0)
316			return ret;
317		goto skip_data;
318
319	case ASN1_OP_MATCH:
320	case ASN1_OP_MATCH_OR_SKIP:
321	case ASN1_OP_MATCH_ANY:
322	case ASN1_OP_COND_MATCH_OR_SKIP:
323	case ASN1_OP_COND_MATCH_ANY:
324	skip_data:
325		if (!(flags & FLAG_CONS)) {
326			if (flags & FLAG_INDEFINITE_LENGTH) {
327				ret = asn1_find_indefinite_length(
328					data, datalen, &dp, &len, &errmsg);
329				if (ret < 0)
330					goto error;
331			} else {
332				dp += len;
333			}
334			pr_debug("- LEAF: %zu\n", len);
335		}
336		pc += asn1_op_lengths[op];
337		goto next_op;
338
339	case ASN1_OP_MATCH_JUMP:
340	case ASN1_OP_MATCH_JUMP_OR_SKIP:
341	case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
342		pr_debug("- MATCH_JUMP\n");
343		if (unlikely(jsp == NR_JUMP_STACK))
344			goto jump_stack_overflow;
345		jump_stack[jsp++] = pc + asn1_op_lengths[op];
346		pc = machine[pc + 2];
347		goto next_op;
348
349	case ASN1_OP_COND_FAIL:
350		if (unlikely(!(flags & FLAG_MATCHED)))
351			goto tag_mismatch;
352		pc += asn1_op_lengths[op];
353		goto next_op;
354
355	case ASN1_OP_COMPLETE:
356		if (unlikely(jsp != 0 || csp != 0)) {
357			pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
358			       jsp, csp);
359			return -EBADMSG;
360		}
361		return 0;
362
363	case ASN1_OP_END_SET:
364	case ASN1_OP_END_SET_ACT:
365		if (unlikely(!(flags & FLAG_MATCHED)))
366			goto tag_mismatch;
367	case ASN1_OP_END_SEQ:
368	case ASN1_OP_END_SET_OF:
369	case ASN1_OP_END_SEQ_OF:
370	case ASN1_OP_END_SEQ_ACT:
371	case ASN1_OP_END_SET_OF_ACT:
372	case ASN1_OP_END_SEQ_OF_ACT:
373		if (unlikely(csp <= 0))
374			goto cons_stack_underflow;
375		csp--;
376		tdp = cons_dp_stack[csp];
377		hdr = cons_hdrlen_stack[csp];
378		len = datalen;
379		datalen = cons_datalen_stack[csp];
380		pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
381			 tdp, dp, len, datalen);
382		if (datalen == 0) {
383			/* Indefinite length - check for the EOC. */
384			datalen = len;
385			if (unlikely(datalen - dp < 2))
386				goto data_overrun_error;
387			if (data[dp++] != 0) {
388				if (op & ASN1_OP_END__OF) {
389					dp--;
390					csp++;
391					pc = machine[pc + 1];
392					pr_debug("- continue\n");
393					goto next_op;
394				}
395				goto missing_eoc;
396			}
397			if (data[dp++] != 0)
398				goto invalid_eoc;
399			len = dp - tdp - 2;
400		} else {
401			if (dp < len && (op & ASN1_OP_END__OF)) {
402				datalen = len;
403				csp++;
404				pc = machine[pc + 1];
405				pr_debug("- continue\n");
406				goto next_op;
407			}
408			if (dp != len)
409				goto cons_length_error;
410			len -= tdp;
411			pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
412		}
413
414		if (op & ASN1_OP_END__ACT) {
415			unsigned char act;
416			if (op & ASN1_OP_END__OF)
417				act = machine[pc + 2];
418			else
419				act = machine[pc + 1];
420			ret = actions[act](context, hdr, 0, data + tdp, len);
421		}
422		pc += asn1_op_lengths[op];
423		goto next_op;
424
425	case ASN1_OP_ACT:
426		ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
427		pc += asn1_op_lengths[op];
428		goto next_op;
429
430	case ASN1_OP_RETURN:
431		if (unlikely(jsp <= 0))
432			goto jump_stack_underflow;
433		pc = jump_stack[--jsp];
434		goto next_op;
435
436	default:
437		break;
438	}
439
440	/* Shouldn't reach here */
441	pr_err("ASN.1 decoder error: Found reserved opcode (%u)\n", op);
442	return -EBADMSG;
443
444data_overrun_error:
445	errmsg = "Data overrun error";
446	goto error;
447machine_overrun_error:
448	errmsg = "Machine overrun error";
449	goto error;
450jump_stack_underflow:
451	errmsg = "Jump stack underflow";
452	goto error;
453jump_stack_overflow:
454	errmsg = "Jump stack overflow";
455	goto error;
456cons_stack_underflow:
457	errmsg = "Cons stack underflow";
458	goto error;
459cons_stack_overflow:
460	errmsg = "Cons stack overflow";
461	goto error;
462cons_length_error:
463	errmsg = "Cons length error";
464	goto error;
465missing_eoc:
466	errmsg = "Missing EOC in indefinite len cons";
467	goto error;
468invalid_eoc:
469	errmsg = "Invalid length EOC";
470	goto error;
471length_too_long:
472	errmsg = "Unsupported length";
473	goto error;
474indefinite_len_primitive:
475	errmsg = "Indefinite len primitive not permitted";
476	goto error;
477tag_mismatch:
478	errmsg = "Unexpected tag";
479	goto error;
480long_tag_not_supported:
481	errmsg = "Long tag not supported";
482error:
483	pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
484		 errmsg, pc, dp, optag, tag, len);
485	return -EBADMSG;
486}
487EXPORT_SYMBOL_GPL(asn1_ber_decoder);
488