1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Decoder for ASN.1 BER/DER/CER encoded bytestream
3 *
4 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8#include <linux/export.h>
9#include <linux/kernel.h>
10#include <linux/errno.h>
11#include <linux/module.h>
12#include <linux/asn1_decoder.h>
13#include <linux/asn1_ber_bytecode.h>
14
15static const unsigned char asn1_op_lengths[ASN1_OP__NR] = {
16	/*					OPC TAG JMP ACT */
17	[ASN1_OP_MATCH]				= 1 + 1,
18	[ASN1_OP_MATCH_OR_SKIP]			= 1 + 1,
19	[ASN1_OP_MATCH_ACT]			= 1 + 1     + 1,
20	[ASN1_OP_MATCH_ACT_OR_SKIP]		= 1 + 1     + 1,
21	[ASN1_OP_MATCH_JUMP]			= 1 + 1 + 1,
22	[ASN1_OP_MATCH_JUMP_OR_SKIP]		= 1 + 1 + 1,
23	[ASN1_OP_MATCH_ANY]			= 1,
24	[ASN1_OP_MATCH_ANY_OR_SKIP]		= 1,
25	[ASN1_OP_MATCH_ANY_ACT]			= 1         + 1,
26	[ASN1_OP_MATCH_ANY_ACT_OR_SKIP]		= 1         + 1,
27	[ASN1_OP_COND_MATCH_OR_SKIP]		= 1 + 1,
28	[ASN1_OP_COND_MATCH_ACT_OR_SKIP]	= 1 + 1     + 1,
29	[ASN1_OP_COND_MATCH_JUMP_OR_SKIP]	= 1 + 1 + 1,
30	[ASN1_OP_COND_MATCH_ANY]		= 1,
31	[ASN1_OP_COND_MATCH_ANY_OR_SKIP]	= 1,
32	[ASN1_OP_COND_MATCH_ANY_ACT]		= 1         + 1,
33	[ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP]	= 1         + 1,
34	[ASN1_OP_COND_FAIL]			= 1,
35	[ASN1_OP_COMPLETE]			= 1,
36	[ASN1_OP_ACT]				= 1         + 1,
37	[ASN1_OP_MAYBE_ACT]			= 1         + 1,
38	[ASN1_OP_RETURN]			= 1,
39	[ASN1_OP_END_SEQ]			= 1,
40	[ASN1_OP_END_SEQ_OF]			= 1     + 1,
41	[ASN1_OP_END_SET]			= 1,
42	[ASN1_OP_END_SET_OF]			= 1     + 1,
43	[ASN1_OP_END_SEQ_ACT]			= 1         + 1,
44	[ASN1_OP_END_SEQ_OF_ACT]		= 1     + 1 + 1,
45	[ASN1_OP_END_SET_ACT]			= 1         + 1,
46	[ASN1_OP_END_SET_OF_ACT]		= 1     + 1 + 1,
47};
48
49/*
50 * Find the length of an indefinite length object
51 * @data: The data buffer
52 * @datalen: The end of the innermost containing element in the buffer
53 * @_dp: The data parse cursor (updated before returning)
54 * @_len: Where to return the size of the element.
55 * @_errmsg: Where to return a pointer to an error message on error
56 */
57static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen,
58				       size_t *_dp, size_t *_len,
59				       const char **_errmsg)
60{
61	unsigned char tag, tmp;
62	size_t dp = *_dp, len, n;
63	int indef_level = 1;
64
65next_tag:
66	if (unlikely(datalen - dp < 2)) {
67		if (datalen == dp)
68			goto missing_eoc;
69		goto data_overrun_error;
70	}
71
72	/* Extract a tag from the data */
73	tag = data[dp++];
74	if (tag == ASN1_EOC) {
75		/* It appears to be an EOC. */
76		if (data[dp++] != 0)
77			goto invalid_eoc;
78		if (--indef_level <= 0) {
79			*_len = dp - *_dp;
80			*_dp = dp;
81			return 0;
82		}
83		goto next_tag;
84	}
85
86	if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) {
87		do {
88			if (unlikely(datalen - dp < 2))
89				goto data_overrun_error;
90			tmp = data[dp++];
91		} while (tmp & 0x80);
92	}
93
94	/* Extract the length */
95	len = data[dp++];
96	if (len <= 0x7f)
97		goto check_length;
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(len) - 1))
109		goto length_too_long;
110	if (unlikely(n > datalen - dp))
111		goto data_overrun_error;
112	len = 0;
113	for (; n > 0; n--) {
114		len <<= 8;
115		len |= data[dp++];
116	}
117check_length:
118	if (len > datalen - dp)
119		goto data_overrun_error;
120	dp += len;
121	goto next_tag;
122
123length_too_long:
124	*_errmsg = "Unsupported length";
125	goto error;
126indefinite_len_primitive:
127	*_errmsg = "Indefinite len primitive not permitted";
128	goto error;
129invalid_eoc:
130	*_errmsg = "Invalid length EOC";
131	goto error;
132data_overrun_error:
133	*_errmsg = "Data overrun error";
134	goto error;
135missing_eoc:
136	*_errmsg = "Missing EOC in indefinite len cons";
137error:
138	*_dp = dp;
139	return -1;
140}
141
142/**
143 * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern
144 * @decoder: The decoder definition (produced by asn1_compiler)
145 * @context: The caller's context (to be passed to the action functions)
146 * @data: The encoded data
147 * @datalen: The size of the encoded data
148 *
149 * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern
150 * produced by asn1_compiler.  Action functions are called on marked tags to
151 * allow the caller to retrieve significant data.
152 *
153 * LIMITATIONS:
154 *
155 * To keep down the amount of stack used by this function, the following limits
156 * have been imposed:
157 *
158 *  (1) This won't handle datalen > 65535 without increasing the size of the
159 *	cons stack elements and length_too_long checking.
160 *
161 *  (2) The stack of constructed types is 10 deep.  If the depth of non-leaf
162 *	constructed types exceeds this, the decode will fail.
163 *
164 *  (3) The SET type (not the SET OF type) isn't really supported as tracking
165 *	what members of the set have been seen is a pain.
166 */
167int asn1_ber_decoder(const struct asn1_decoder *decoder,
168		     void *context,
169		     const unsigned char *data,
170		     size_t datalen)
171{
172	const unsigned char *machine = decoder->machine;
173	const asn1_action_t *actions = decoder->actions;
174	size_t machlen = decoder->machlen;
175	enum asn1_opcode op;
176	unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0;
177	const char *errmsg;
178	size_t pc = 0, dp = 0, tdp = 0, len = 0;
179	int ret;
180
181	unsigned char flags = 0;
182#define FLAG_INDEFINITE_LENGTH	0x01
183#define FLAG_MATCHED		0x02
184#define FLAG_LAST_MATCHED	0x04 /* Last tag matched */
185#define FLAG_CONS		0x20 /* Corresponds to CONS bit in the opcode tag
186				      * - ie. whether or not we are going to parse
187				      *   a compound type.
188				      */
189
190#define NR_CONS_STACK 10
191	unsigned short cons_dp_stack[NR_CONS_STACK];
192	unsigned short cons_datalen_stack[NR_CONS_STACK];
193	unsigned char cons_hdrlen_stack[NR_CONS_STACK];
194#define NR_JUMP_STACK 10
195	unsigned char jump_stack[NR_JUMP_STACK];
196
197	if (datalen > 65535)
198		return -EMSGSIZE;
199
200next_op:
201	pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n",
202		 pc, machlen, dp, datalen, csp, jsp);
203	if (unlikely(pc >= machlen))
204		goto machine_overrun_error;
205	op = machine[pc];
206	if (unlikely(pc + asn1_op_lengths[op] > machlen))
207		goto machine_overrun_error;
208
209	/* If this command is meant to match a tag, then do that before
210	 * evaluating the command.
211	 */
212	if (op <= ASN1_OP__MATCHES_TAG) {
213		unsigned char tmp;
214
215		/* Skip conditional matches if possible */
216		if ((op & ASN1_OP_MATCH__COND && flags & FLAG_MATCHED) ||
217		    (op & ASN1_OP_MATCH__SKIP && dp == datalen)) {
218			flags &= ~FLAG_LAST_MATCHED;
219			pc += asn1_op_lengths[op];
220			goto next_op;
221		}
222
223		flags = 0;
224		hdr = 2;
225
226		/* Extract a tag from the data */
227		if (unlikely(datalen - dp < 2))
228			goto data_overrun_error;
229		tag = data[dp++];
230		if (unlikely((tag & 0x1f) == ASN1_LONG_TAG))
231			goto long_tag_not_supported;
232
233		if (op & ASN1_OP_MATCH__ANY) {
234			pr_debug("- any %02x\n", tag);
235		} else {
236			/* Extract the tag from the machine
237			 * - Either CONS or PRIM are permitted in the data if
238			 *   CONS is not set in the op stream, otherwise CONS
239			 *   is mandatory.
240			 */
241			optag = machine[pc + 1];
242			flags |= optag & FLAG_CONS;
243
244			/* Determine whether the tag matched */
245			tmp = optag ^ tag;
246			tmp &= ~(optag & ASN1_CONS_BIT);
247			pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp);
248			if (tmp != 0) {
249				/* All odd-numbered tags are MATCH_OR_SKIP. */
250				if (op & ASN1_OP_MATCH__SKIP) {
251					pc += asn1_op_lengths[op];
252					dp--;
253					goto next_op;
254				}
255				goto tag_mismatch;
256			}
257		}
258		flags |= FLAG_MATCHED;
259
260		len = data[dp++];
261		if (len > 0x7f) {
262			if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
263				/* Indefinite length */
264				if (unlikely(!(tag & ASN1_CONS_BIT)))
265					goto indefinite_len_primitive;
266				flags |= FLAG_INDEFINITE_LENGTH;
267				if (unlikely(2 > datalen - dp))
268					goto data_overrun_error;
269			} else {
270				int n = len - 0x80;
271				if (unlikely(n > 2))
272					goto length_too_long;
273				if (unlikely(n > datalen - dp))
274					goto data_overrun_error;
275				hdr += n;
276				for (len = 0; n > 0; n--) {
277					len <<= 8;
278					len |= data[dp++];
279				}
280				if (unlikely(len > datalen - dp))
281					goto data_overrun_error;
282			}
283		} else {
284			if (unlikely(len > datalen - dp))
285				goto data_overrun_error;
286		}
287
288		if (flags & FLAG_CONS) {
289			/* For expected compound forms, we stack the positions
290			 * of the start and end of the data.
291			 */
292			if (unlikely(csp >= NR_CONS_STACK))
293				goto cons_stack_overflow;
294			cons_dp_stack[csp] = dp;
295			cons_hdrlen_stack[csp] = hdr;
296			if (!(flags & FLAG_INDEFINITE_LENGTH)) {
297				cons_datalen_stack[csp] = datalen;
298				datalen = dp + len;
299			} else {
300				cons_datalen_stack[csp] = 0;
301			}
302			csp++;
303		}
304
305		pr_debug("- TAG: %02x %zu%s\n",
306			 tag, len, flags & FLAG_CONS ? " CONS" : "");
307		tdp = dp;
308	}
309
310	/* Decide how to handle the operation */
311	switch (op) {
312	case ASN1_OP_MATCH:
313	case ASN1_OP_MATCH_OR_SKIP:
314	case ASN1_OP_MATCH_ACT:
315	case ASN1_OP_MATCH_ACT_OR_SKIP:
316	case ASN1_OP_MATCH_ANY:
317	case ASN1_OP_MATCH_ANY_OR_SKIP:
318	case ASN1_OP_MATCH_ANY_ACT:
319	case ASN1_OP_MATCH_ANY_ACT_OR_SKIP:
320	case ASN1_OP_COND_MATCH_OR_SKIP:
321	case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
322	case ASN1_OP_COND_MATCH_ANY:
323	case ASN1_OP_COND_MATCH_ANY_OR_SKIP:
324	case ASN1_OP_COND_MATCH_ANY_ACT:
325	case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP:
326
327		if (!(flags & FLAG_CONS)) {
328			if (flags & FLAG_INDEFINITE_LENGTH) {
329				size_t tmp = dp;
330
331				ret = asn1_find_indefinite_length(
332					data, datalen, &tmp, &len, &errmsg);
333				if (ret < 0)
334					goto error;
335			}
336			pr_debug("- LEAF: %zu\n", len);
337		}
338
339		if (op & ASN1_OP_MATCH__ACT) {
340			unsigned char act;
341
342			if (op & ASN1_OP_MATCH__ANY)
343				act = machine[pc + 1];
344			else
345				act = machine[pc + 2];
346			ret = actions[act](context, hdr, tag, data + dp, len);
347			if (ret < 0)
348				return ret;
349		}
350
351		if (!(flags & FLAG_CONS))
352			dp += len;
353		pc += asn1_op_lengths[op];
354		goto next_op;
355
356	case ASN1_OP_MATCH_JUMP:
357	case ASN1_OP_MATCH_JUMP_OR_SKIP:
358	case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
359		pr_debug("- MATCH_JUMP\n");
360		if (unlikely(jsp == NR_JUMP_STACK))
361			goto jump_stack_overflow;
362		jump_stack[jsp++] = pc + asn1_op_lengths[op];
363		pc = machine[pc + 2];
364		goto next_op;
365
366	case ASN1_OP_COND_FAIL:
367		if (unlikely(!(flags & FLAG_MATCHED)))
368			goto tag_mismatch;
369		pc += asn1_op_lengths[op];
370		goto next_op;
371
372	case ASN1_OP_COMPLETE:
373		if (unlikely(jsp != 0 || csp != 0)) {
374			pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
375			       jsp, csp);
376			return -EBADMSG;
377		}
378		return 0;
379
380	case ASN1_OP_END_SET:
381	case ASN1_OP_END_SET_ACT:
382		if (unlikely(!(flags & FLAG_MATCHED)))
383			goto tag_mismatch;
384		fallthrough;
385
386	case ASN1_OP_END_SEQ:
387	case ASN1_OP_END_SET_OF:
388	case ASN1_OP_END_SEQ_OF:
389	case ASN1_OP_END_SEQ_ACT:
390	case ASN1_OP_END_SET_OF_ACT:
391	case ASN1_OP_END_SEQ_OF_ACT:
392		if (unlikely(csp <= 0))
393			goto cons_stack_underflow;
394		csp--;
395		tdp = cons_dp_stack[csp];
396		hdr = cons_hdrlen_stack[csp];
397		len = datalen;
398		datalen = cons_datalen_stack[csp];
399		pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
400			 tdp, dp, len, datalen);
401		if (datalen == 0) {
402			/* Indefinite length - check for the EOC. */
403			datalen = len;
404			if (unlikely(datalen - dp < 2))
405				goto data_overrun_error;
406			if (data[dp++] != 0) {
407				if (op & ASN1_OP_END__OF) {
408					dp--;
409					csp++;
410					pc = machine[pc + 1];
411					pr_debug("- continue\n");
412					goto next_op;
413				}
414				goto missing_eoc;
415			}
416			if (data[dp++] != 0)
417				goto invalid_eoc;
418			len = dp - tdp - 2;
419		} else {
420			if (dp < len && (op & ASN1_OP_END__OF)) {
421				datalen = len;
422				csp++;
423				pc = machine[pc + 1];
424				pr_debug("- continue\n");
425				goto next_op;
426			}
427			if (dp != len)
428				goto cons_length_error;
429			len -= tdp;
430			pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
431		}
432
433		if (op & ASN1_OP_END__ACT) {
434			unsigned char act;
435			if (op & ASN1_OP_END__OF)
436				act = machine[pc + 2];
437			else
438				act = machine[pc + 1];
439			ret = actions[act](context, hdr, 0, data + tdp, len);
440			if (ret < 0)
441				return ret;
442		}
443		pc += asn1_op_lengths[op];
444		goto next_op;
445
446	case ASN1_OP_MAYBE_ACT:
447		if (!(flags & FLAG_LAST_MATCHED)) {
448			pc += asn1_op_lengths[op];
449			goto next_op;
450		}
451		fallthrough;
452
453	case ASN1_OP_ACT:
454		ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
455		if (ret < 0)
456			return ret;
457		pc += asn1_op_lengths[op];
458		goto next_op;
459
460	case ASN1_OP_RETURN:
461		if (unlikely(jsp <= 0))
462			goto jump_stack_underflow;
463		pc = jump_stack[--jsp];
464		flags |= FLAG_MATCHED | FLAG_LAST_MATCHED;
465		goto next_op;
466
467	default:
468		break;
469	}
470
471	/* Shouldn't reach here */
472	pr_err("ASN.1 decoder error: Found reserved opcode (%u) pc=%zu\n",
473	       op, pc);
474	return -EBADMSG;
475
476data_overrun_error:
477	errmsg = "Data overrun error";
478	goto error;
479machine_overrun_error:
480	errmsg = "Machine overrun error";
481	goto error;
482jump_stack_underflow:
483	errmsg = "Jump stack underflow";
484	goto error;
485jump_stack_overflow:
486	errmsg = "Jump stack overflow";
487	goto error;
488cons_stack_underflow:
489	errmsg = "Cons stack underflow";
490	goto error;
491cons_stack_overflow:
492	errmsg = "Cons stack overflow";
493	goto error;
494cons_length_error:
495	errmsg = "Cons length error";
496	goto error;
497missing_eoc:
498	errmsg = "Missing EOC in indefinite len cons";
499	goto error;
500invalid_eoc:
501	errmsg = "Invalid length EOC";
502	goto error;
503length_too_long:
504	errmsg = "Unsupported length";
505	goto error;
506indefinite_len_primitive:
507	errmsg = "Indefinite len primitive not permitted";
508	goto error;
509tag_mismatch:
510	errmsg = "Unexpected tag";
511	goto error;
512long_tag_not_supported:
513	errmsg = "Long tag not supported";
514error:
515	pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
516		 errmsg, pc, dp, optag, tag, len);
517	return -EBADMSG;
518}
519EXPORT_SYMBOL_GPL(asn1_ber_decoder);
520
521MODULE_LICENSE("GPL");
522