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
15 static 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 */
57 static 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
65 next_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 }
117 check_length:
118 if (len > datalen - dp)
119 goto data_overrun_error;
120 dp += len;
121 goto next_tag;
122
123 length_too_long:
124 *_errmsg = "Unsupported length";
125 goto error;
126 indefinite_len_primitive:
127 *_errmsg = "Indefinite len primitive not permitted";
128 goto error;
129 invalid_eoc:
130 *_errmsg = "Invalid length EOC";
131 goto error;
132 data_overrun_error:
133 *_errmsg = "Data overrun error";
134 goto error;
135 missing_eoc:
136 *_errmsg = "Missing EOC in indefinite len cons";
137 error:
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 */
167 int 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
200 next_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
476 data_overrun_error:
477 errmsg = "Data overrun error";
478 goto error;
479 machine_overrun_error:
480 errmsg = "Machine overrun error";
481 goto error;
482 jump_stack_underflow:
483 errmsg = "Jump stack underflow";
484 goto error;
485 jump_stack_overflow:
486 errmsg = "Jump stack overflow";
487 goto error;
488 cons_stack_underflow:
489 errmsg = "Cons stack underflow";
490 goto error;
491 cons_stack_overflow:
492 errmsg = "Cons stack overflow";
493 goto error;
494 cons_length_error:
495 errmsg = "Cons length error";
496 goto error;
497 missing_eoc:
498 errmsg = "Missing EOC in indefinite len cons";
499 goto error;
500 invalid_eoc:
501 errmsg = "Invalid length EOC";
502 goto error;
503 length_too_long:
504 errmsg = "Unsupported length";
505 goto error;
506 indefinite_len_primitive:
507 errmsg = "Indefinite len primitive not permitted";
508 goto error;
509 tag_mismatch:
510 errmsg = "Unexpected tag";
511 goto error;
512 long_tag_not_supported:
513 errmsg = "Long tag not supported";
514 error:
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 }
519 EXPORT_SYMBOL_GPL(asn1_ber_decoder);
520
521 MODULE_LICENSE("GPL");
522
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