[v3] Add CA enforcement keyring restrictions

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

Posted by Eric Snowberg 2 years, 9 months ago

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(+)

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 */
 };
 
 /*
-- 
2.27.0

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

Posted by Jarkko Sakkinen 2 years, 8 months ago

On Tue, Dec 13, 2022 at 07:33:54PM -0500, Eric Snowberg wrote:
> 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.

Please add:

Link: https://www.rfc-editor.org/rfc/rfc5280 # 4.2.1.9. Basic Constraints
 
> 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(+)
> 
> 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;

Why this instead of either:

1. Each check in separate if-statement.
2. All in a single statement:
   vlen < 2 || v[0] != (ASN1_CONS_BIT | ASN1_SEQ) || v[1] != vlen - 2

It would be also nice to have some sort of explanation in a comment, given
the cryptic statement and the amount of magic numbers in it. I.e. in plain
English what does the check actually means.


> +		if (vlen >= 4 && v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
> +			ctx->cert->root_ca = true;

Ditto for the explanation part. I have really hard time deciphering this.

> +	}
> +
>  	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 */
>  };
>  
>  /*
> -- 
> 2.27.0
> 

BR, Jarkko

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

Posted by Mimi Zohar 2 years, 9 months ago

> 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?

-- 

thanks,

Mimi

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

Posted by Jarkko Sakkinen 2 years, 8 months ago

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?

BR, Jarkko

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

Posted by Eric Snowberg 2 years, 8 months ago


> 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/

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

Posted by Mimi Zohar 2 years, 8 months ago

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.

-- 
thanks,

Mimi