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Linux/lib/asn1_decoder.c

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  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 
 18 static 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_OR_SKIP]             = 1,
 28         [ASN1_OP_MATCH_ANY_ACT]                 = 1         + 1,
 29         [ASN1_OP_MATCH_ANY_ACT_OR_SKIP]         = 1         + 1,
 30         [ASN1_OP_COND_MATCH_OR_SKIP]            = 1 + 1,
 31         [ASN1_OP_COND_MATCH_ACT_OR_SKIP]        = 1 + 1     + 1,
 32         [ASN1_OP_COND_MATCH_JUMP_OR_SKIP]       = 1 + 1 + 1,
 33         [ASN1_OP_COND_MATCH_ANY]                = 1,
 34         [ASN1_OP_COND_MATCH_ANY_OR_SKIP]        = 1,
 35         [ASN1_OP_COND_MATCH_ANY_ACT]            = 1         + 1,
 36         [ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP]    = 1         + 1,
 37         [ASN1_OP_COND_FAIL]                     = 1,
 38         [ASN1_OP_COMPLETE]                      = 1,
 39         [ASN1_OP_ACT]                           = 1         + 1,
 40         [ASN1_OP_MAYBE_ACT]                     = 1         + 1,
 41         [ASN1_OP_RETURN]                        = 1,
 42         [ASN1_OP_END_SEQ]                       = 1,
 43         [ASN1_OP_END_SEQ_OF]                    = 1     + 1,
 44         [ASN1_OP_END_SET]                       = 1,
 45         [ASN1_OP_END_SET_OF]                    = 1     + 1,
 46         [ASN1_OP_END_SEQ_ACT]                   = 1         + 1,
 47         [ASN1_OP_END_SEQ_OF_ACT]                = 1     + 1 + 1,
 48         [ASN1_OP_END_SET_ACT]                   = 1         + 1,
 49         [ASN1_OP_END_SET_OF_ACT]                = 1     + 1 + 1,
 50 };
 51 
 52 /*
 53  * Find the length of an indefinite length object
 54  * @data: The data buffer
 55  * @datalen: The end of the innermost containing element in the buffer
 56  * @_dp: The data parse cursor (updated before returning)
 57  * @_len: Where to return the size of the element.
 58  * @_errmsg: Where to return a pointer to an error message on error
 59  */
 60 static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen,
 61                                        size_t *_dp, size_t *_len,
 62                                        const char **_errmsg)
 63 {
 64         unsigned char tag, tmp;
 65         size_t dp = *_dp, len, n;
 66         int indef_level = 1;
 67 
 68 next_tag:
 69         if (unlikely(datalen - dp < 2)) {
 70                 if (datalen == dp)
 71                         goto missing_eoc;
 72                 goto data_overrun_error;
 73         }
 74 
 75         /* Extract a tag from the data */
 76         tag = data[dp++];
 77         if (tag == 0) {
 78                 /* It appears to be an EOC. */
 79                 if (data[dp++] != 0)
 80                         goto invalid_eoc;
 81                 if (--indef_level <= 0) {
 82                         *_len = dp - *_dp;
 83                         *_dp = dp;
 84                         return 0;
 85                 }
 86                 goto next_tag;
 87         }
 88 
 89         if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) {
 90                 do {
 91                         if (unlikely(datalen - dp < 2))
 92                                 goto data_overrun_error;
 93                         tmp = data[dp++];
 94                 } while (tmp & 0x80);
 95         }
 96 
 97         /* Extract the length */
 98         len = data[dp++];
 99         if (len <= 0x7f) {
100                 dp += len;
101                 goto next_tag;
102         }
103 
104         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
105                 /* Indefinite length */
106                 if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5))
107                         goto indefinite_len_primitive;
108                 indef_level++;
109                 goto next_tag;
110         }
111 
112         n = len - 0x80;
113         if (unlikely(n > sizeof(size_t) - 1))
114                 goto length_too_long;
115         if (unlikely(n > datalen - dp))
116                 goto data_overrun_error;
117         for (len = 0; n > 0; n--) {
118                 len <<= 8;
119                 len |= data[dp++];
120         }
121         dp += len;
122         goto next_tag;
123 
124 length_too_long:
125         *_errmsg = "Unsupported length";
126         goto error;
127 indefinite_len_primitive:
128         *_errmsg = "Indefinite len primitive not permitted";
129         goto error;
130 invalid_eoc:
131         *_errmsg = "Invalid length EOC";
132         goto error;
133 data_overrun_error:
134         *_errmsg = "Data overrun error";
135         goto error;
136 missing_eoc:
137         *_errmsg = "Missing EOC in indefinite len cons";
138 error:
139         *_dp = dp;
140         return -1;
141 }
142 
143 /**
144  * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern
145  * @decoder: The decoder definition (produced by asn1_compiler)
146  * @context: The caller's context (to be passed to the action functions)
147  * @data: The encoded data
148  * @datalen: The size of the encoded data
149  *
150  * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern
151  * produced by asn1_compiler.  Action functions are called on marked tags to
152  * allow the caller to retrieve significant data.
153  *
154  * LIMITATIONS:
155  *
156  * To keep down the amount of stack used by this function, the following limits
157  * have been imposed:
158  *
159  *  (1) This won't handle datalen > 65535 without increasing the size of the
160  *      cons stack elements and length_too_long checking.
161  *
162  *  (2) The stack of constructed types is 10 deep.  If the depth of non-leaf
163  *      constructed types exceeds this, the decode will fail.
164  *
165  *  (3) The SET type (not the SET OF type) isn't really supported as tracking
166  *      what members of the set have been seen is a pain.
167  */
168 int asn1_ber_decoder(const struct asn1_decoder *decoder,
169                      void *context,
170                      const unsigned char *data,
171                      size_t datalen)
172 {
173         const unsigned char *machine = decoder->machine;
174         const asn1_action_t *actions = decoder->actions;
175         size_t machlen = decoder->machlen;
176         enum asn1_opcode op;
177         unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0;
178         const char *errmsg;
179         size_t pc = 0, dp = 0, tdp = 0, len = 0;
180         int ret;
181 
182         unsigned char flags = 0;
183 #define FLAG_INDEFINITE_LENGTH  0x01
184 #define FLAG_MATCHED            0x02
185 #define FLAG_LAST_MATCHED       0x04 /* Last tag matched */
186 #define FLAG_CONS               0x20 /* Corresponds to CONS bit in the opcode tag
187                                       * - ie. whether or not we are going to parse
188                                       *   a compound type.
189                                       */
190 
191 #define NR_CONS_STACK 10
192         unsigned short cons_dp_stack[NR_CONS_STACK];
193         unsigned short cons_datalen_stack[NR_CONS_STACK];
194         unsigned char cons_hdrlen_stack[NR_CONS_STACK];
195 #define NR_JUMP_STACK 10
196         unsigned char jump_stack[NR_JUMP_STACK];
197 
198         if (datalen > 65535)
199                 return -EMSGSIZE;
200 
201 next_op:
202         pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n",
203                  pc, machlen, dp, datalen, csp, jsp);
204         if (unlikely(pc >= machlen))
205                 goto machine_overrun_error;
206         op = machine[pc];
207         if (unlikely(pc + asn1_op_lengths[op] > machlen))
208                 goto machine_overrun_error;
209 
210         /* If this command is meant to match a tag, then do that before
211          * evaluating the command.
212          */
213         if (op <= ASN1_OP__MATCHES_TAG) {
214                 unsigned char tmp;
215 
216                 /* Skip conditional matches if possible */
217                 if ((op & ASN1_OP_MATCH__COND && flags & FLAG_MATCHED) ||
218                     (op & ASN1_OP_MATCH__SKIP && dp == datalen)) {
219                         flags &= ~FLAG_LAST_MATCHED;
220                         pc += asn1_op_lengths[op];
221                         goto next_op;
222                 }
223 
224                 flags = 0;
225                 hdr = 2;
226 
227                 /* Extract a tag from the data */
228                 if (unlikely(dp >= datalen - 1))
229                         goto data_overrun_error;
230                 tag = data[dp++];
231                 if (unlikely((tag & 0x1f) == ASN1_LONG_TAG))
232                         goto long_tag_not_supported;
233 
234                 if (op & ASN1_OP_MATCH__ANY) {
235                         pr_debug("- any %02x\n", tag);
236                 } else {
237                         /* Extract the tag from the machine
238                          * - Either CONS or PRIM are permitted in the data if
239                          *   CONS is not set in the op stream, otherwise CONS
240                          *   is mandatory.
241                          */
242                         optag = machine[pc + 1];
243                         flags |= optag & FLAG_CONS;
244 
245                         /* Determine whether the tag matched */
246                         tmp = optag ^ tag;
247                         tmp &= ~(optag & ASN1_CONS_BIT);
248                         pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp);
249                         if (tmp != 0) {
250                                 /* All odd-numbered tags are MATCH_OR_SKIP. */
251                                 if (op & ASN1_OP_MATCH__SKIP) {
252                                         pc += asn1_op_lengths[op];
253                                         dp--;
254                                         goto next_op;
255                                 }
256                                 goto tag_mismatch;
257                         }
258                 }
259                 flags |= FLAG_MATCHED;
260 
261                 len = data[dp++];
262                 if (len > 0x7f) {
263                         if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
264                                 /* Indefinite length */
265                                 if (unlikely(!(tag & ASN1_CONS_BIT)))
266                                         goto indefinite_len_primitive;
267                                 flags |= FLAG_INDEFINITE_LENGTH;
268                                 if (unlikely(2 > datalen - dp))
269                                         goto data_overrun_error;
270                         } else {
271                                 int n = len - 0x80;
272                                 if (unlikely(n > 2))
273                                         goto length_too_long;
274                                 if (unlikely(dp >= datalen - n))
275                                         goto data_overrun_error;
276                                 hdr += n;
277                                 for (len = 0; n > 0; n--) {
278                                         len <<= 8;
279                                         len |= data[dp++];
280                                 }
281                                 if (unlikely(len > datalen - dp))
282                                         goto data_overrun_error;
283                         }
284                 }
285 
286                 if (flags & FLAG_CONS) {
287                         /* For expected compound forms, we stack the positions
288                          * of the start and end of the data.
289                          */
290                         if (unlikely(csp >= NR_CONS_STACK))
291                                 goto cons_stack_overflow;
292                         cons_dp_stack[csp] = dp;
293                         cons_hdrlen_stack[csp] = hdr;
294                         if (!(flags & FLAG_INDEFINITE_LENGTH)) {
295                                 cons_datalen_stack[csp] = datalen;
296                                 datalen = dp + len;
297                         } else {
298                                 cons_datalen_stack[csp] = 0;
299                         }
300                         csp++;
301                 }
302 
303                 pr_debug("- TAG: %02x %zu%s\n",
304                          tag, len, flags & FLAG_CONS ? " CONS" : "");
305                 tdp = dp;
306         }
307 
308         /* Decide how to handle the operation */
309         switch (op) {
310         case ASN1_OP_MATCH_ANY_ACT:
311         case ASN1_OP_MATCH_ANY_ACT_OR_SKIP:
312         case ASN1_OP_COND_MATCH_ANY_ACT:
313         case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP:
314                 ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len);
315                 if (ret < 0)
316                         return ret;
317                 goto skip_data;
318 
319         case ASN1_OP_MATCH_ACT:
320         case ASN1_OP_MATCH_ACT_OR_SKIP:
321         case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
322                 ret = actions[machine[pc + 2]](context, hdr, tag, data + dp, len);
323                 if (ret < 0)
324                         return ret;
325                 goto skip_data;
326 
327         case ASN1_OP_MATCH:
328         case ASN1_OP_MATCH_OR_SKIP:
329         case ASN1_OP_MATCH_ANY:
330         case ASN1_OP_MATCH_ANY_OR_SKIP:
331         case ASN1_OP_COND_MATCH_OR_SKIP:
332         case ASN1_OP_COND_MATCH_ANY:
333         case ASN1_OP_COND_MATCH_ANY_OR_SKIP:
334         skip_data:
335                 if (!(flags & FLAG_CONS)) {
336                         if (flags & FLAG_INDEFINITE_LENGTH) {
337                                 ret = asn1_find_indefinite_length(
338                                         data, datalen, &dp, &len, &errmsg);
339                                 if (ret < 0)
340                                         goto error;
341                         } else {
342                                 dp += len;
343                         }
344                         pr_debug("- LEAF: %zu\n", len);
345                 }
346                 pc += asn1_op_lengths[op];
347                 goto next_op;
348 
349         case ASN1_OP_MATCH_JUMP:
350         case ASN1_OP_MATCH_JUMP_OR_SKIP:
351         case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
352                 pr_debug("- MATCH_JUMP\n");
353                 if (unlikely(jsp == NR_JUMP_STACK))
354                         goto jump_stack_overflow;
355                 jump_stack[jsp++] = pc + asn1_op_lengths[op];
356                 pc = machine[pc + 2];
357                 goto next_op;
358 
359         case ASN1_OP_COND_FAIL:
360                 if (unlikely(!(flags & FLAG_MATCHED)))
361                         goto tag_mismatch;
362                 pc += asn1_op_lengths[op];
363                 goto next_op;
364 
365         case ASN1_OP_COMPLETE:
366                 if (unlikely(jsp != 0 || csp != 0)) {
367                         pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
368                                jsp, csp);
369                         return -EBADMSG;
370                 }
371                 return 0;
372 
373         case ASN1_OP_END_SET:
374         case ASN1_OP_END_SET_ACT:
375                 if (unlikely(!(flags & FLAG_MATCHED)))
376                         goto tag_mismatch;
377         case ASN1_OP_END_SEQ:
378         case ASN1_OP_END_SET_OF:
379         case ASN1_OP_END_SEQ_OF:
380         case ASN1_OP_END_SEQ_ACT:
381         case ASN1_OP_END_SET_OF_ACT:
382         case ASN1_OP_END_SEQ_OF_ACT:
383                 if (unlikely(csp <= 0))
384                         goto cons_stack_underflow;
385                 csp--;
386                 tdp = cons_dp_stack[csp];
387                 hdr = cons_hdrlen_stack[csp];
388                 len = datalen;
389                 datalen = cons_datalen_stack[csp];
390                 pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
391                          tdp, dp, len, datalen);
392                 if (datalen == 0) {
393                         /* Indefinite length - check for the EOC. */
394                         datalen = len;
395                         if (unlikely(datalen - dp < 2))
396                                 goto data_overrun_error;
397                         if (data[dp++] != 0) {
398                                 if (op & ASN1_OP_END__OF) {
399                                         dp--;
400                                         csp++;
401                                         pc = machine[pc + 1];
402                                         pr_debug("- continue\n");
403                                         goto next_op;
404                                 }
405                                 goto missing_eoc;
406                         }
407                         if (data[dp++] != 0)
408                                 goto invalid_eoc;
409                         len = dp - tdp - 2;
410                 } else {
411                         if (dp < len && (op & ASN1_OP_END__OF)) {
412                                 datalen = len;
413                                 csp++;
414                                 pc = machine[pc + 1];
415                                 pr_debug("- continue\n");
416                                 goto next_op;
417                         }
418                         if (dp != len)
419                                 goto cons_length_error;
420                         len -= tdp;
421                         pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
422                 }
423 
424                 if (op & ASN1_OP_END__ACT) {
425                         unsigned char act;
426                         if (op & ASN1_OP_END__OF)
427                                 act = machine[pc + 2];
428                         else
429                                 act = machine[pc + 1];
430                         ret = actions[act](context, hdr, 0, data + tdp, len);
431                 }
432                 pc += asn1_op_lengths[op];
433                 goto next_op;
434 
435         case ASN1_OP_MAYBE_ACT:
436                 if (!(flags & FLAG_LAST_MATCHED)) {
437                         pc += asn1_op_lengths[op];
438                         goto next_op;
439                 }
440         case ASN1_OP_ACT:
441                 ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
442                 if (ret < 0)
443                         return ret;
444                 pc += asn1_op_lengths[op];
445                 goto next_op;
446 
447         case ASN1_OP_RETURN:
448                 if (unlikely(jsp <= 0))
449                         goto jump_stack_underflow;
450                 pc = jump_stack[--jsp];
451                 flags |= FLAG_MATCHED | FLAG_LAST_MATCHED;
452                 goto next_op;
453 
454         default:
455                 break;
456         }
457 
458         /* Shouldn't reach here */
459         pr_err("ASN.1 decoder error: Found reserved opcode (%u) pc=%zu\n",
460                op, pc);
461         return -EBADMSG;
462 
463 data_overrun_error:
464         errmsg = "Data overrun error";
465         goto error;
466 machine_overrun_error:
467         errmsg = "Machine overrun error";
468         goto error;
469 jump_stack_underflow:
470         errmsg = "Jump stack underflow";
471         goto error;
472 jump_stack_overflow:
473         errmsg = "Jump stack overflow";
474         goto error;
475 cons_stack_underflow:
476         errmsg = "Cons stack underflow";
477         goto error;
478 cons_stack_overflow:
479         errmsg = "Cons stack overflow";
480         goto error;
481 cons_length_error:
482         errmsg = "Cons length error";
483         goto error;
484 missing_eoc:
485         errmsg = "Missing EOC in indefinite len cons";
486         goto error;
487 invalid_eoc:
488         errmsg = "Invalid length EOC";
489         goto error;
490 length_too_long:
491         errmsg = "Unsupported length";
492         goto error;
493 indefinite_len_primitive:
494         errmsg = "Indefinite len primitive not permitted";
495         goto error;
496 tag_mismatch:
497         errmsg = "Unexpected tag";
498         goto error;
499 long_tag_not_supported:
500         errmsg = "Long tag not supported";
501 error:
502         pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
503                  errmsg, pc, dp, optag, tag, len);
504         return -EBADMSG;
505 }
506 EXPORT_SYMBOL_GPL(asn1_ber_decoder);
507 

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