summaryrefslogtreecommitdiff
path: root/crypto/asymmetric_keys/x509_cert_parser.c
blob: 487204d394266e74be91e1b47beb25eecfdc8f54 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
// SPDX-License-Identifier: GPL-2.0-or-later
/* X.509 certificate parser
 *
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#define pr_fmt(fmt) "X.509: "fmt
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/oid_registry.h>
#include <crypto/public_key.h>
#include "x509_parser.h"
#include "x509.asn1.h"
#include "x509_akid.asn1.h"

struct x509_parse_context {
	struct x509_certificate	*cert;		/* Certificate being constructed */
	unsigned long	data;			/* Start of data */
	const void	*key;			/* Key data */
	size_t		key_size;		/* Size of key data */
	const void	*params;		/* Key parameters */
	size_t		params_size;		/* Size of key parameters */
	enum OID	key_algo;		/* Algorithm used by the cert's key */
	enum OID	last_oid;		/* Last OID encountered */
	enum OID	sig_algo;		/* Algorithm used to sign the cert */
	u8		o_size;			/* Size of organizationName (O) */
	u8		cn_size;		/* Size of commonName (CN) */
	u8		email_size;		/* Size of emailAddress */
	u16		o_offset;		/* Offset of organizationName (O) */
	u16		cn_offset;		/* Offset of commonName (CN) */
	u16		email_offset;		/* Offset of emailAddress */
	unsigned	raw_akid_size;
	const void	*raw_akid;		/* Raw authorityKeyId in ASN.1 */
	const void	*akid_raw_issuer;	/* Raw directoryName in authorityKeyId */
	unsigned	akid_raw_issuer_size;
};

/*
 * Free an X.509 certificate
 */
void x509_free_certificate(struct x509_certificate *cert)
{
	if (cert) {
		public_key_free(cert->pub);
		public_key_signature_free(cert->sig);
		kfree(cert->issuer);
		kfree(cert->subject);
		kfree(cert->id);
		kfree(cert->skid);
		kfree(cert);
	}
}
EXPORT_SYMBOL_GPL(x509_free_certificate);

/*
 * Parse an X.509 certificate
 */
struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
{
	struct x509_certificate *cert;
	struct x509_parse_context *ctx;
	struct asymmetric_key_id *kid;
	long ret;

	ret = -ENOMEM;
	cert = kzalloc(sizeof(struct x509_certificate), GFP_KERNEL);
	if (!cert)
		goto error_no_cert;
	cert->pub = kzalloc(sizeof(struct public_key), GFP_KERNEL);
	if (!cert->pub)
		goto error_no_ctx;
	cert->sig = kzalloc(sizeof(struct public_key_signature), GFP_KERNEL);
	if (!cert->sig)
		goto error_no_ctx;
	ctx = kzalloc(sizeof(struct x509_parse_context), GFP_KERNEL);
	if (!ctx)
		goto error_no_ctx;

	ctx->cert = cert;
	ctx->data = (unsigned long)data;

	/* Attempt to decode the certificate */
	ret = asn1_ber_decoder(&x509_decoder, ctx, data, datalen);
	if (ret < 0)
		goto error_decode;

	/* Decode the AuthorityKeyIdentifier */
	if (ctx->raw_akid) {
		pr_devel("AKID: %u %*phN\n",
			 ctx->raw_akid_size, ctx->raw_akid_size, ctx->raw_akid);
		ret = asn1_ber_decoder(&x509_akid_decoder, ctx,
				       ctx->raw_akid, ctx->raw_akid_size);
		if (ret < 0) {
			pr_warn("Couldn't decode AuthKeyIdentifier\n");
			goto error_decode;
		}
	}

	ret = -ENOMEM;
	cert->pub->key = kmemdup(ctx->key, ctx->key_size, GFP_KERNEL);
	if (!cert->pub->key)
		goto error_decode;

	cert->pub->keylen = ctx->key_size;

	cert->pub->params = kmemdup(ctx->params, ctx->params_size, GFP_KERNEL);
	if (!cert->pub->params)
		goto error_decode;

	cert->pub->paramlen = ctx->params_size;
	cert->pub->algo = ctx->key_algo;

	/* Grab the signature bits */
	ret = x509_get_sig_params(cert);
	if (ret < 0)
		goto error_decode;

	/* Generate cert issuer + serial number key ID */
	kid = asymmetric_key_generate_id(cert->raw_serial,
					 cert->raw_serial_size,
					 cert->raw_issuer,
					 cert->raw_issuer_size);
	if (IS_ERR(kid)) {
		ret = PTR_ERR(kid);
		goto error_decode;
	}
	cert->id = kid;

	/* Detect self-signed certificates */
	ret = x509_check_for_self_signed(cert);
	if (ret < 0)
		goto error_decode;

	kfree(ctx);
	return cert;

error_decode:
	kfree(ctx);
error_no_ctx:
	x509_free_certificate(cert);
error_no_cert:
	return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(x509_cert_parse);

/*
 * Note an OID when we find one for later processing when we know how
 * to interpret it.
 */
int x509_note_OID(void *context, size_t hdrlen,
	     unsigned char tag,
	     const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;

	ctx->last_oid = look_up_OID(value, vlen);
	if (ctx->last_oid == OID__NR) {
		char buffer[50];
		sprint_oid(value, vlen, buffer, sizeof(buffer));
		pr_debug("Unknown OID: [%lu] %s\n",
			 (unsigned long)value - ctx->data, buffer);
	}
	return 0;
}

/*
 * Save the position of the TBS data so that we can check the signature over it
 * later.
 */
int x509_note_tbs_certificate(void *context, size_t hdrlen,
			      unsigned char tag,
			      const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;

	pr_debug("x509_note_tbs_certificate(,%zu,%02x,%ld,%zu)!\n",
		 hdrlen, tag, (unsigned long)value - ctx->data, vlen);

	ctx->cert->tbs = value - hdrlen;
	ctx->cert->tbs_size = vlen + hdrlen;
	return 0;
}

/*
 * Record the algorithm that was used to sign this certificate.
 */
int x509_note_sig_algo(void *context, size_t hdrlen, unsigned char tag,
		       const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;

	pr_debug("PubKey Algo: %u\n", ctx->last_oid);

	switch (ctx->last_oid) {
	default:
		return -ENOPKG; /* Unsupported combination */

	case OID_sha256WithRSAEncryption:
		ctx->cert->sig->hash_algo = "sha256";
		goto rsa_pkcs1;

	case OID_sha384WithRSAEncryption:
		ctx->cert->sig->hash_algo = "sha384";
		goto rsa_pkcs1;

	case OID_sha512WithRSAEncryption:
		ctx->cert->sig->hash_algo = "sha512";
		goto rsa_pkcs1;

	case OID_sha224WithRSAEncryption:
		ctx->cert->sig->hash_algo = "sha224";
		goto rsa_pkcs1;

	case OID_id_rsassa_pkcs1_v1_5_with_sha3_256:
		ctx->cert->sig->hash_algo = "sha3-256";
		goto rsa_pkcs1;

	case OID_id_rsassa_pkcs1_v1_5_with_sha3_384:
		ctx->cert->sig->hash_algo = "sha3-384";
		goto rsa_pkcs1;

	case OID_id_rsassa_pkcs1_v1_5_with_sha3_512:
		ctx->cert->sig->hash_algo = "sha3-512";
		goto rsa_pkcs1;

	case OID_id_ecdsa_with_sha224:
		ctx->cert->sig->hash_algo = "sha224";
		goto ecdsa;

	case OID_id_ecdsa_with_sha256:
		ctx->cert->sig->hash_algo = "sha256";
		goto ecdsa;

	case OID_id_ecdsa_with_sha384:
		ctx->cert->sig->hash_algo = "sha384";
		goto ecdsa;

	case OID_id_ecdsa_with_sha512:
		ctx->cert->sig->hash_algo = "sha512";
		goto ecdsa;

	case OID_id_ecdsa_with_sha3_256:
		ctx->cert->sig->hash_algo = "sha3-256";
		goto ecdsa;

	case OID_id_ecdsa_with_sha3_384:
		ctx->cert->sig->hash_algo = "sha3-384";
		goto ecdsa;

	case OID_id_ecdsa_with_sha3_512:
		ctx->cert->sig->hash_algo = "sha3-512";
		goto ecdsa;

	case OID_gost2012Signature256:
		ctx->cert->sig->hash_algo = "streebog256";
		goto ecrdsa;

	case OID_gost2012Signature512:
		ctx->cert->sig->hash_algo = "streebog512";
		goto ecrdsa;

	case OID_SM2_with_SM3:
		ctx->cert->sig->hash_algo = "sm3";
		goto sm2;
	}

rsa_pkcs1:
	ctx->cert->sig->pkey_algo = "rsa";
	ctx->cert->sig->encoding = "pkcs1";
	ctx->sig_algo = ctx->last_oid;
	return 0;
ecrdsa:
	ctx->cert->sig->pkey_algo = "ecrdsa";
	ctx->cert->sig->encoding = "raw";
	ctx->sig_algo = ctx->last_oid;
	return 0;
sm2:
	ctx->cert->sig->pkey_algo = "sm2";
	ctx->cert->sig->encoding = "raw";
	ctx->sig_algo = ctx->last_oid;
	return 0;
ecdsa:
	ctx->cert->sig->pkey_algo = "ecdsa";
	ctx->cert->sig->encoding = "x962";
	ctx->sig_algo = ctx->last_oid;
	return 0;
}

/*
 * Note the whereabouts and type of the signature.
 */
int x509_note_signature(void *context, size_t hdrlen,
			unsigned char tag,
			const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;

	pr_debug("Signature: alg=%u, size=%zu\n", ctx->last_oid, vlen);

	/*
	 * In X.509 certificates, the signature's algorithm is stored in two
	 * places: inside the TBSCertificate (the data that is signed), and
	 * alongside the signature.  These *must* match.
	 */
	if (ctx->last_oid != ctx->sig_algo) {
		pr_warn("signatureAlgorithm (%u) differs from tbsCertificate.signature (%u)\n",
			ctx->last_oid, ctx->sig_algo);
		return -EINVAL;
	}

	if (strcmp(ctx->cert->sig->pkey_algo, "rsa") == 0 ||
	    strcmp(ctx->cert->sig->pkey_algo, "ecrdsa") == 0 ||
	    strcmp(ctx->cert->sig->pkey_algo, "sm2") == 0 ||
	    strcmp(ctx->cert->sig->pkey_algo, "ecdsa") == 0) {
		/* Discard the BIT STRING metadata */
		if (vlen < 1 || *(const u8 *)value != 0)
			return -EBADMSG;

		value++;
		vlen--;
	}

	ctx->cert->raw_sig = value;
	ctx->cert->raw_sig_size = vlen;
	return 0;
}

/*
 * Note the certificate serial number
 */
int x509_note_serial(void *context, size_t hdrlen,
		     unsigned char tag,
		     const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;
	ctx->cert->raw_serial = value;
	ctx->cert->raw_serial_size = vlen;
	return 0;
}

/*
 * Note some of the name segments from which we'll fabricate a name.
 */
int x509_extract_name_segment(void *context, size_t hdrlen,
			      unsigned char tag,
			      const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;

	switch (ctx->last_oid) {
	case OID_commonName:
		ctx->cn_size = vlen;
		ctx->cn_offset = (unsigned long)value - ctx->data;
		break;
	case OID_organizationName:
		ctx->o_size = vlen;
		ctx->o_offset = (unsigned long)value - ctx->data;
		break;
	case OID_email_address:
		ctx->email_size = vlen;
		ctx->email_offset = (unsigned long)value - ctx->data;
		break;
	default:
		break;
	}

	return 0;
}

/*
 * Fabricate and save the issuer and subject names
 */
static int x509_fabricate_name(struct x509_parse_context *ctx, size_t hdrlen,
			       unsigned char tag,
			       char **_name, size_t vlen)
{
	const void *name, *data = (const void *)ctx->data;
	size_t namesize;
	char *buffer;

	if (*_name)
		return -EINVAL;

	/* Empty name string if no material */
	if (!ctx->cn_size && !ctx->o_size && !ctx->email_size) {
		buffer = kmalloc(1, GFP_KERNEL);
		if (!buffer)
			return -ENOMEM;
		buffer[0] = 0;
		goto done;
	}

	if (ctx->cn_size && ctx->o_size) {
		/* Consider combining O and CN, but use only the CN if it is
		 * prefixed by the O, or a significant portion thereof.
		 */
		namesize = ctx->cn_size;
		name = data + ctx->cn_offset;
		if (ctx->cn_size >= ctx->o_size &&
		    memcmp(data + ctx->cn_offset, data + ctx->o_offset,
			   ctx->o_size) == 0)
			goto single_component;
		if (ctx->cn_size >= 7 &&
		    ctx->o_size >= 7 &&
		    memcmp(data + ctx->cn_offset, data + ctx->o_offset, 7) == 0)
			goto single_component;

		buffer = kmalloc(ctx->o_size + 2 + ctx->cn_size + 1,
				 GFP_KERNEL);
		if (!buffer)
			return -ENOMEM;

		memcpy(buffer,
		       data + ctx->o_offset, ctx->o_size);
		buffer[ctx->o_size + 0] = ':';
		buffer[ctx->o_size + 1] = ' ';
		memcpy(buffer + ctx->o_size + 2,
		       data + ctx->cn_offset, ctx->cn_size);
		buffer[ctx->o_size + 2 + ctx->cn_size] = 0;
		goto done;

	} else if (ctx->cn_size) {
		namesize = ctx->cn_size;
		name = data + ctx->cn_offset;
	} else if (ctx->o_size) {
		namesize = ctx->o_size;
		name = data + ctx->o_offset;
	} else {
		namesize = ctx->email_size;
		name = data + ctx->email_offset;
	}

single_component:
	buffer = kmalloc(namesize + 1, GFP_KERNEL);
	if (!buffer)
		return -ENOMEM;
	memcpy(buffer, name, namesize);
	buffer[namesize] = 0;

done:
	*_name = buffer;
	ctx->cn_size = 0;
	ctx->o_size = 0;
	ctx->email_size = 0;
	return 0;
}

int x509_note_issuer(void *context, size_t hdrlen,
		     unsigned char tag,
		     const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;
	struct asymmetric_key_id *kid;

	ctx->cert->raw_issuer = value;
	ctx->cert->raw_issuer_size = vlen;

	if (!ctx->cert->sig->auth_ids[2]) {
		kid = asymmetric_key_generate_id(value, vlen, "", 0);
		if (IS_ERR(kid))
			return PTR_ERR(kid);
		ctx->cert->sig->auth_ids[2] = kid;
	}

	return x509_fabricate_name(ctx, hdrlen, tag, &ctx->cert->issuer, vlen);
}

int x509_note_subject(void *context, size_t hdrlen,
		      unsigned char tag,
		      const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;
	ctx->cert->raw_subject = value;
	ctx->cert->raw_subject_size = vlen;
	return x509_fabricate_name(ctx, hdrlen, tag, &ctx->cert->subject, vlen);
}

/*
 * Extract the parameters for the public key
 */
int x509_note_params(void *context, size_t hdrlen,
		     unsigned char tag,
		     const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;

	/*
	 * AlgorithmIdentifier is used three times in the x509, we should skip
	 * first and ignore third, using second one which is after subject and
	 * before subjectPublicKey.
	 */
	if (!ctx->cert->raw_subject || ctx->key)
		return 0;
	ctx->params = value - hdrlen;
	ctx->params_size = vlen + hdrlen;
	return 0;
}

/*
 * Extract the data for the public key algorithm
 */
int x509_extract_key_data(void *context, size_t hdrlen,
			  unsigned char tag,
			  const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;
	enum OID oid;

	ctx->key_algo = ctx->last_oid;
	switch (ctx->last_oid) {
	case OID_rsaEncryption:
		ctx->cert->pub->pkey_algo = "rsa";
		break;
	case OID_gost2012PKey256:
	case OID_gost2012PKey512:
		ctx->cert->pub->pkey_algo = "ecrdsa";
		break;
	case OID_sm2:
		ctx->cert->pub->pkey_algo = "sm2";
		break;
	case OID_id_ecPublicKey:
		if (parse_OID(ctx->params, ctx->params_size, &oid) != 0)
			return -EBADMSG;

		switch (oid) {
		case OID_sm2:
			ctx->cert->pub->pkey_algo = "sm2";
			break;
		case OID_id_prime192v1:
			ctx->cert->pub->pkey_algo = "ecdsa-nist-p192";
			break;
		case OID_id_prime256v1:
			ctx->cert->pub->pkey_algo = "ecdsa-nist-p256";
			break;
		case OID_id_ansip384r1:
			ctx->cert->pub->pkey_algo = "ecdsa-nist-p384";
			break;
		default:
			return -ENOPKG;
		}
		break;
	default:
		return -ENOPKG;
	}

	/* Discard the BIT STRING metadata */
	if (vlen < 1 || *(const u8 *)value != 0)
		return -EBADMSG;
	ctx->key = value + 1;
	ctx->key_size = vlen - 1;
	return 0;
}

/* The keyIdentifier in AuthorityKeyIdentifier SEQUENCE is tag(CONT,PRIM,0) */
#define SEQ_TAG_KEYID (ASN1_CONT << 6)

/*
 * Process certificate extensions that are used to qualify the certificate.
 */
int x509_process_extension(void *context, size_t hdrlen,
			   unsigned char tag,
			   const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;
	struct asymmetric_key_id *kid;
	const unsigned char *v = value;

	pr_debug("Extension: %u\n", ctx->last_oid);

	if (ctx->last_oid == OID_subjectKeyIdentifier) {
		/* Get hold of the key fingerprint */
		if (ctx->cert->skid || vlen < 3)
			return -EBADMSG;
		if (v[0] != ASN1_OTS || v[1] != vlen - 2)
			return -EBADMSG;
		v += 2;
		vlen -= 2;

		ctx->cert->raw_skid_size = vlen;
		ctx->cert->raw_skid = v;
		kid = asymmetric_key_generate_id(v, vlen, "", 0);
		if (IS_ERR(kid))
			return PTR_ERR(kid);
		ctx->cert->skid = kid;
		pr_debug("subjkeyid %*phN\n", kid->len, kid->data);
		return 0;
	}

	if (ctx->last_oid == OID_keyUsage) {
		/*
		 * Get hold of the keyUsage bit string
		 * v[1] is the encoding size
		 *       (Expect either 0x02 or 0x03, making it 1 or 2 bytes)
		 * v[2] is the number of unused bits in the bit string
		 *       (If >= 3 keyCertSign is missing when v[1] = 0x02)
		 * v[3] and possibly v[4] contain the bit string
		 *
		 * From RFC 5280 4.2.1.3:
		 *   0x04 is where keyCertSign lands in this bit string
		 *   0x80 is where digitalSignature lands in this bit string
		 */
		if (v[0] != ASN1_BTS)
			return -EBADMSG;
		if (vlen < 4)
			return -EBADMSG;
		if (v[2] >= 8)
			return -EBADMSG;
		if (v[3] & 0x80)
			ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_DIGITALSIG;
		if (v[1] == 0x02 && v[2] <= 2 && (v[3] & 0x04))
			ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_KEYCERTSIGN;
		else if (vlen > 4 && v[1] == 0x03 && (v[3] & 0x04))
			ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_KEYCERTSIGN;
		return 0;
	}

	if (ctx->last_oid == OID_authorityKeyIdentifier) {
		/* Get hold of the CA key fingerprint */
		ctx->raw_akid = v;
		ctx->raw_akid_size = vlen;
		return 0;
	}

	if (ctx->last_oid == OID_basicConstraints) {
		/*
		 * Get hold of the basicConstraints
		 * v[1] is the encoding size
		 *	(Expect 0x2 or greater, making it 1 or more bytes)
		 * v[2] is the encoding type
		 *	(Expect an ASN1_BOOL for the CA)
		 * v[3] is the contents of the ASN1_BOOL
		 *      (Expect 1 if the CA is TRUE)
		 * vlen should match the entire extension size
		 */
		if (v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
			return -EBADMSG;
		if (vlen < 2)
			return -EBADMSG;
		if (v[1] != vlen - 2)
			return -EBADMSG;
		if (vlen >= 4 && v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
			ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_CA;
		return 0;
	}

	return 0;
}

/**
 * x509_decode_time - Decode an X.509 time ASN.1 object
 * @_t: The time to fill in
 * @hdrlen: The length of the object header
 * @tag: The object tag
 * @value: The object value
 * @vlen: The size of the object value
 *
 * Decode an ASN.1 universal time or generalised time field into a struct the
 * kernel can handle and check it for validity.  The time is decoded thus:
 *
 *	[RFC5280 §4.1.2.5]
 *	CAs conforming to this profile MUST always encode certificate validity
 *	dates through the year 2049 as UTCTime; certificate validity dates in
 *	2050 or later MUST be encoded as GeneralizedTime.  Conforming
 *	applications MUST be able to process validity dates that are encoded in
 *	either UTCTime or GeneralizedTime.
 */
int x509_decode_time(time64_t *_t,  size_t hdrlen,
		     unsigned char tag,
		     const unsigned char *value, size_t vlen)
{
	static const unsigned char month_lengths[] = { 31, 28, 31, 30, 31, 30,
						       31, 31, 30, 31, 30, 31 };
	const unsigned char *p = value;
	unsigned year, mon, day, hour, min, sec, mon_len;

#define dec2bin(X) ({ unsigned char x = (X) - '0'; if (x > 9) goto invalid_time; x; })
#define DD2bin(P) ({ unsigned x = dec2bin(P[0]) * 10 + dec2bin(P[1]); P += 2; x; })

	if (tag == ASN1_UNITIM) {
		/* UTCTime: YYMMDDHHMMSSZ */
		if (vlen != 13)
			goto unsupported_time;
		year = DD2bin(p);
		if (year >= 50)
			year += 1900;
		else
			year += 2000;
	} else if (tag == ASN1_GENTIM) {
		/* GenTime: YYYYMMDDHHMMSSZ */
		if (vlen != 15)
			goto unsupported_time;
		year = DD2bin(p) * 100 + DD2bin(p);
		if (year >= 1950 && year <= 2049)
			goto invalid_time;
	} else {
		goto unsupported_time;
	}

	mon  = DD2bin(p);
	day = DD2bin(p);
	hour = DD2bin(p);
	min  = DD2bin(p);
	sec  = DD2bin(p);

	if (*p != 'Z')
		goto unsupported_time;

	if (year < 1970 ||
	    mon < 1 || mon > 12)
		goto invalid_time;

	mon_len = month_lengths[mon - 1];
	if (mon == 2) {
		if (year % 4 == 0) {
			mon_len = 29;
			if (year % 100 == 0) {
				mon_len = 28;
				if (year % 400 == 0)
					mon_len = 29;
			}
		}
	}

	if (day < 1 || day > mon_len ||
	    hour > 24 || /* ISO 8601 permits 24:00:00 as midnight tomorrow */
	    min > 59 ||
	    sec > 60) /* ISO 8601 permits leap seconds [X.680 46.3] */
		goto invalid_time;

	*_t = mktime64(year, mon, day, hour, min, sec);
	return 0;

unsupported_time:
	pr_debug("Got unsupported time [tag %02x]: '%*phN'\n",
		 tag, (int)vlen, value);
	return -EBADMSG;
invalid_time:
	pr_debug("Got invalid time [tag %02x]: '%*phN'\n",
		 tag, (int)vlen, value);
	return -EBADMSG;
}
EXPORT_SYMBOL_GPL(x509_decode_time);

int x509_note_not_before(void *context, size_t hdrlen,
			 unsigned char tag,
			 const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;
	return x509_decode_time(&ctx->cert->valid_from, hdrlen, tag, value, vlen);
}

int x509_note_not_after(void *context, size_t hdrlen,
			unsigned char tag,
			const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;
	return x509_decode_time(&ctx->cert->valid_to, hdrlen, tag, value, vlen);
}

/*
 * Note a key identifier-based AuthorityKeyIdentifier
 */
int x509_akid_note_kid(void *context, size_t hdrlen,
		       unsigned char tag,
		       const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;
	struct asymmetric_key_id *kid;

	pr_debug("AKID: keyid: %*phN\n", (int)vlen, value);

	if (ctx->cert->sig->auth_ids[1])
		return 0;

	kid = asymmetric_key_generate_id(value, vlen, "", 0);
	if (IS_ERR(kid))
		return PTR_ERR(kid);
	pr_debug("authkeyid %*phN\n", kid->len, kid->data);
	ctx->cert->sig->auth_ids[1] = kid;
	return 0;
}

/*
 * Note a directoryName in an AuthorityKeyIdentifier
 */
int x509_akid_note_name(void *context, size_t hdrlen,
			unsigned char tag,
			const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;

	pr_debug("AKID: name: %*phN\n", (int)vlen, value);

	ctx->akid_raw_issuer = value;
	ctx->akid_raw_issuer_size = vlen;
	return 0;
}

/*
 * Note a serial number in an AuthorityKeyIdentifier
 */
int x509_akid_note_serial(void *context, size_t hdrlen,
			  unsigned char tag,
			  const void *value, size_t vlen)
{
	struct x509_parse_context *ctx = context;
	struct asymmetric_key_id *kid;

	pr_debug("AKID: serial: %*phN\n", (int)vlen, value);

	if (!ctx->akid_raw_issuer || ctx->cert->sig->auth_ids[0])
		return 0;

	kid = asymmetric_key_generate_id(value,
					 vlen,
					 ctx->akid_raw_issuer,
					 ctx->akid_raw_issuer_size);
	if (IS_ERR(kid))
		return PTR_ERR(kid);

	pr_debug("authkeyid %*phN\n", kid->len, kid->data);
	ctx->cert->sig->auth_ids[0] = kid;
	return 0;
}