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@oracle.com>
---
v7: Initial version
v8: Moved key_is_ca after key_is_private, recommended by Mimi
---
 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 6d003096b5bc..f4299b8a4926 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c

@@ -571,6 +571,15 @@ 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 a9b2e600b7cc..72dcbc06ef9c 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;
 };

-- 
2.18.4