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[v3,03/10] KEYS: X.509: Parse Basic Constraints for CA

Message ID 20221214003401.4086781-4-eric.snowberg@oracle.com
State New
Headers show
Series Add CA enforcement keyring restrictions | expand

Commit Message

Eric Snowberg Dec. 14, 2022, 12:33 a.m. UTC
Parse the X.509 Basic Constraints.  The basic constraints extension
identifies whether the subject of the certificate is a CA.

BasicConstraints ::= SEQUENCE {
        cA                      BOOLEAN DEFAULT FALSE,
        pathLenConstraint       INTEGER (0..MAX) OPTIONAL }

If the CA is true, store it in the x509_certificate.  This will be used
in a follow on patch that requires knowing if the public key is a CA.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
 crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
 crypto/asymmetric_keys/x509_parser.h      | 1 +
 2 files changed, 10 insertions(+)

Comments

Mimi Zohar Dec. 15, 2022, 11:10 a.m. UTC | #1
> diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
> index a299c9c56f40..7c5c0ad1c22e 100644
> --- a/crypto/asymmetric_keys/x509_parser.h
> +++ b/crypto/asymmetric_keys/x509_parser.h
> @@ -38,6 +38,7 @@ struct x509_certificate {
>  	bool		self_signed;		/* T if self-signed (check unsupported_sig too) */
>  	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
>  	bool		blacklisted;
> +	bool		root_ca;		/* T if basic constraints CA is set */
>  }; 

The variable "root_ca" should probably be renamed to just "ca", right?
Eric Snowberg Jan. 4, 2023, 8:14 p.m. UTC | #2
> On Jan 4, 2023, at 5:29 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> 
> On Thu, Dec 15, 2022 at 06:10:04AM -0500, Mimi Zohar wrote:
>>> diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
>>> index a299c9c56f40..7c5c0ad1c22e 100644
>>> --- a/crypto/asymmetric_keys/x509_parser.h
>>> +++ b/crypto/asymmetric_keys/x509_parser.h
>>> @@ -38,6 +38,7 @@ struct x509_certificate {
>>> 	bool		self_signed;		/* T if self-signed (check unsupported_sig too) */
>>> 	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
>>> 	bool		blacklisted;
>>> +	bool		root_ca;		/* T if basic constraints CA is set */
>>> }; 
>> 
>> The variable "root_ca" should probably be renamed to just "ca", right?
> 
> Perhaps is_ca?

I am open to renaming this, but need an agreement on whether the “is_” should be used or not:

https://lore.kernel.org/lkml/b28ea211d88e968a5487b20477236e9b507755f4.camel@linux.ibm.com/
Mimi Zohar Jan. 4, 2023, 10:38 p.m. UTC | #3
On Wed, 2023-01-04 at 20:14 +0000, Eric Snowberg wrote:
> 
> > On Jan 4, 2023, at 5:29 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> > 
> > On Thu, Dec 15, 2022 at 06:10:04AM -0500, Mimi Zohar wrote:
> >>> diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
> >>> index a299c9c56f40..7c5c0ad1c22e 100644
> >>> --- a/crypto/asymmetric_keys/x509_parser.h
> >>> +++ b/crypto/asymmetric_keys/x509_parser.h
> >>> @@ -38,6 +38,7 @@ struct x509_certificate {
> >>> 	bool		self_signed;		/* T if self-signed (check unsupported_sig too) */
> >>> 	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
> >>> 	bool		blacklisted;
> >>> +	bool		root_ca;		/* T if basic constraints CA is set */
> >>> }; 
> >> 
> >> The variable "root_ca" should probably be renamed to just "ca", right?
> > 
> > Perhaps is_ca?
> 
> I am open to renaming this, but need an agreement on whether the “is_” should be used or not:
> 
> https://lore.kernel.org/lkml/b28ea211d88e968a5487b20477236e9b507755f4.camel@linux.ibm.com/

Examples of both functions and variables exist that are prefixed with
"is_".   One is a question; the other a statement.   Naming the
variable "is_ca" and using it like "if (cert->is_ca)" does make sense.
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Patch

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 7a9b084e2043..b4443e507153 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -586,6 +586,15 @@  int x509_process_extension(void *context, size_t hdrlen,
 		return 0;
 	}
 
+	if (ctx->last_oid == OID_basicConstraints) {
+		if (vlen < 2 || v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
+			return -EBADMSG;
+		if (v[1] != vlen - 2)
+			return -EBADMSG;
+		if (vlen >= 4 && v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
+			ctx->cert->root_ca = true;
+	}
+
 	return 0;
 }
 
diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
index a299c9c56f40..7c5c0ad1c22e 100644
--- a/crypto/asymmetric_keys/x509_parser.h
+++ b/crypto/asymmetric_keys/x509_parser.h
@@ -38,6 +38,7 @@  struct x509_certificate {
 	bool		self_signed;		/* T if self-signed (check unsupported_sig too) */
 	bool		unsupported_sig;	/* T if signature uses unsupported crypto */
 	bool		blacklisted;
+	bool		root_ca;		/* T if basic constraints CA is set */
 };
 
 /*