Re: [PATCH v3 04/10] KEYS: X.509: Parse Key Usage

Eric Snowberg
2023-01-04T21:47:34Z

> On Jan 4, 2023, at 4:43 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
>
> On Tue, Dec 13, 2022 at 07:33:55PM -0500, Eric Snowberg wrote:
>> Parse the X.509 Key Usage. The key usage extension defines the purpose of
>> the key contained in the certificate.
>>
>> id-ce-keyUsage OBJECT IDENTIFIER ::= { id-ce 15 }
>>
>> KeyUsage ::= BIT STRING {
>> digitalSignature (0),
>> contentCommitment (1),
>> keyEncipherment (2),
>> dataEncipherment (3),
>> keyAgreement (4),
>> keyCertSign (5),
>> cRLSign (6),
>> encipherOnly (7),
>> decipherOnly (8) }
>>
>> If the keyCertSign is set, store it in the x509_certificate structure.
>> This will be used in a follow on patch that requires knowing the
>> certificate key usage type.
>>
>> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
>> ---
>> crypto/asymmetric_keys/x509_cert_parser.c | 22 ++++++++++++++++++++++
>> crypto/asymmetric_keys/x509_parser.h | 1 +
>> 2 files changed, 23 insertions(+)
>>
>> diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
>> index b4443e507153..edb22cf04eed 100644
>> --- a/crypto/asymmetric_keys/x509_cert_parser.c
>> +++ b/crypto/asymmetric_keys/x509_cert_parser.c
>> @@ -579,6 +579,28 @@ int x509_process_extension(void *context, size_t hdrlen,
>> return 0;
>> }
>>
>> + if (ctx->last_oid == OID_keyUsage) {
>> + /*
>> + * Get hold of the keyUsage bit string to validate keyCertSign
>> + * 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)
>> + * v[3] and possibly v[4] contain the bit string
>> + * 0x04 is where KeyCertSign lands in this bit string (from
>> + * RFC 5280 4.2.1.3)
>> + */
>> + if (v[0] != ASN1_BTS)
>> + return -EBADMSG;
>> + if (vlen < 4)
>> + return -EBADMSG;
>> + if (v[1] == 0x02 && v[2] <= 2 && (v[3] & 0x04))
>> + ctx->cert->kcs_set = true;
>> + else if (vlen > 4 && v[1] == 0x03 && (v[3] & 0x04))
>> + ctx->cert->kcs_set = true;
>> + return 0;
>
> This is much more easier to follow thanks to explanation.
>
>> + }
>> +
>> if (ctx->last_oid == OID_authorityKeyIdentifier) {
>> /* Get hold of the CA key fingerprint */
>> ctx->raw_akid = v;
>> diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
>> index 7c5c0ad1c22e..74a9f929e400 100644
>> --- a/crypto/asymmetric_keys/x509_parser.h
>> +++ b/crypto/asymmetric_keys/x509_parser.h
>> @@ -39,6 +39,7 @@ struct x509_certificate {
>> bool unsupported_sig; /* T if signature uses unsupported crypto */
>> bool blacklisted;
>> bool root_ca; /* T if basic constraints CA is set */
>> + bool kcs_set; /* T if keyCertSign is set */
>> };
>>
>> /*
>> --
>> 2.27.0
>>
>
> LGTM but I'll hold with reviewed-by's up until the patch set overally
> looks good to me and I have actually tested it.

Thanks for your review. I will make all the other changes you brought up with
the other patches in the next round.