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Date: Fri, 29 Mar 2013 16:51:21 +0800
From: joeyli <jlee@...e.com>
To: rusty@...tcorp.com.au, dhowells@...hat.com
Cc: linux-kernel@...r.kernel.org, Josh Boyer <jwboyer@...hat.com>,
Randy Dunlap <rdunlap@...otime.net>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v2] X.509: Support parse long form of length octets in
Authority Key Identifier
於 四，2013-03-14 於 15:34 +0800，Lee, Chun-Yi 提到：
> From: Chun-Yi Lee <jlee@...e.com>
>
> Per X.509 spec in 4.2.1.1 section, the structure of Authority Key
> Identifier Extension is:
>
> AuthorityKeyIdentifier ::= SEQUENCE {
> keyIdentifier [0] KeyIdentifier OPTIONAL,
> authorityCertIssuer [1] GeneralNames OPTIONAL,
> authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL }
>
> KeyIdentifier ::= OCTET STRING
>
> When a certificate also provides
> authorityCertIssuer and authorityCertSerialNumber then the length of
> AuthorityKeyIdentifier SEQUENCE is likely to long form format.
> e.g.
> The example certificate demos/tunala/A-server.pem in openssl source:
>
> X509v3 Authority Key Identifier:
> keyid:49:FB:45:72:12:C4:CC:E1:45:A1:D3:08:9E:95:C4:2C:6D:55:3F:17
> DirName:/C=NZ/L=Wellington/O=Really Irresponsible Authorisation Authority (RIAA)/OU=Cert-stamping/CN=Jackov al-Trades/emailAddress=none@...e.domain
> serial:00
>
> Current parsing rule of OID_authorityKeyIdentifier only take care the
> short form format, it causes load certificate to modsign_keyring fail:
>
> [ 12.061147] X.509: Extension: 47
> [ 12.075121] MODSIGN: Problem loading in-kernel X.509 certificate (-74)
>
> So, this patch add the parsing rule for support long form format against
> Authority Key Identifier.
>
> v2:
> - Removed comma from author's name.
> - Moved 'Short Form length' comment inside the if-body.
> - Changed the type of sub to size_t.
> - Use ASN1_INDEFINITE_LENGTH rather than writing 0x80 and 127.
> - Moved the key_len's value assignment before alter v.
> - Fixed the typo of octets.
> - Add 2 to v before entering the loop for calculate the length.
> - Removed the comment of check vlen.
>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Josh Boyer <jwboyer@...hat.com>
> Cc: Randy Dunlap <rdunlap@...otime.net>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: "David S. Miller" <davem@...emloft.net>
> Acked-by: David Howells <dhowells@...hat.com>
> Signed-off-by: Chun-Yi Lee <jlee@...e.com>
> ---
> crypto/asymmetric_keys/x509_cert_parser.c | 55 ++++++++++++++++++++++++----
> 1 files changed, 47 insertions(+), 8 deletions(-)
>
> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
> index 7fabc4c..59ab6d2 100644
> --- a/crypto/asymmetric_keys/x509_cert_parser.c
> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
> @@ -373,6 +373,9 @@ int rsa_extract_mpi(void *context, size_t hdrlen,
> 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.
> */
> @@ -407,21 +410,57 @@ int x509_process_extension(void *context, size_t hdrlen,
> }
>
> if (ctx->last_oid == OID_authorityKeyIdentifier) {
> + size_t key_len;
> +
> /* Get hold of the CA key fingerprint */
> if (vlen < 5)
> return -EBADMSG;
> - if (v[0] != (ASN1_SEQ | (ASN1_CONS << 5)) ||
> - v[1] != vlen - 2 ||
> - v[2] != (ASN1_CONT << 6) ||
> - v[3] != vlen - 4)
> +
> + /* Authority Key Identifier must be a Constructed SEQUENCE */
> + if (v[0] != (ASN1_SEQ | (ASN1_CONS << 5)))
> return -EBADMSG;
> - v += 4;
> - vlen -= 4;
>
> - f = kmalloc(vlen * 2 + 1, GFP_KERNEL);
> + /* Authority Key Identifier is not indefinite length */
> + if (unlikely(vlen == ASN1_INDEFINITE_LENGTH))
> + return -EBADMSG;
> +
> + if (vlen < ASN1_INDEFINITE_LENGTH) {
> + /* Short Form length */
> + if (v[1] != vlen - 2 ||
> + v[2] != SEQ_TAG_KEYID ||
> + v[3] != vlen - 4)
In "Short Form length" case, there still possible have
authorityCertIssuer and authorityCertSerialNumber
in AuthorityKeyIdentifier sequence. In the case, the v[3], length of
keyIdentifier doesn't equal to "vlen - 4".
So, we should change the size check to "v[3] > vlen - 4" for cover
this situation.
I will send out the version 3 patch.
Thanks a lot!
Joey Lee
> + return -EBADMSG;
> +
> + key_len = v[3];
> + v += 4;
> + } else {
> + /* Long Form length */
> + size_t seq_len = 0;
> + size_t sub = v[1] - ASN1_INDEFINITE_LENGTH;
> +
> + if (sub > 2)
> + return -EBADMSG;
> +
> + /* calculate the length from subsequent octets */
> + v += 2;
> + for (i = 0; i < sub; i++) {
> + seq_len <<= 8;
> + seq_len |= v[i];
> + }
> +
> + if (seq_len != vlen - 2 - sub ||
> + v[sub] != SEQ_TAG_KEYID ||
> + v[sub + 1] > vlen - 4 - sub)
> + return -EBADMSG;
> +
> + key_len = v[sub + 1];
> + v += (sub + 2);
> + }
> +
> + f = kmalloc(key_len * 2 + 1, GFP_KERNEL);
> if (!f)
> return -ENOMEM;
> - for (i = 0; i < vlen; i++)
> + for (i = 0; i < key_len; i++)
> sprintf(f + i * 2, "%02x", v[i]);
> pr_debug("authority %s\n", f);
> ctx->cert->authority = f;
--
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