Root/lib/asn1_decoder.c

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 * @datasize: 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

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