linux-kernel - [PATCH 2/4] X.509: Parse Basic Constraints for CA

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Message-Id: <20220301173651.3435350-3-eric.snowberg@oracle.com>
Date:   Tue,  1 Mar 2022 12:36:49 -0500
From:   Eric Snowberg <eric.snowberg@...cle.com>
To:     zohar@...ux.ibm.com, jarkko@...nel.org, dhowells@...hat.com,
        dwmw2@...radead.org
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        jmorris@...ei.org, serge@...lyn.com, eric.snowberg@...cle.com,
        stefanb@...ux.ibm.com, nayna@...ux.ibm.com,
        mic@...ux.microsoft.com, konrad.wilk@...cle.com,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: [PATCH 2/4] X.509: Parse Basic Constraints for CA

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 a new public_key field call key_is_ca.
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@...cle.com>
---
 crypto/asymmetric_keys/x509_cert_parser.c | 9 +++++++++
 include/crypto/public_key.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 2899ed80bb18..38c907f4ce27 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -583,6 +583,15 @@ int x509_process_extension(void *context, size_t hdrlen,
 		return 0;
 	}
 
+	if (ctx->last_oid == OID_basicConstraints) {
+		if (v[0] != (ASN1_CONS_BIT | ASN1_SEQ))
+			return -EBADMSG;
+		if (v[1] != vlen - 2)
+			return -EBADMSG;
+		if (v[1] != 0 && v[2] == ASN1_BOOL && v[3] == 1)
+			ctx->cert->pub->key_is_ca = true;
+	}
+
 	return 0;
 }
 
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index 6d61695e1cde..0521241764b7 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -26,6 +26,7 @@ struct public_key {
 	void *params;
 	u32 paramlen;
 	bool key_is_private;
+	bool key_is_ca;
 	const char *id_type;
 	const char *pkey_algo;
 };
-- 
2.27.0