linux-kernel - [PATCH 2/7] KEYS: X.509: Parse Basic Constraints for CA

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Message-Id: <20220406015337.4000739-3-eric.snowberg@oracle.com>
Date:   Tue,  5 Apr 2022 21:53:32 -0400
From:   Eric Snowberg <eric.snowberg@...cle.com>
To:     dhowells@...hat.com, dwmw2@...radead.org, jarkko@...nel.org,
        zohar@...ux.ibm.com, linux-integrity@...r.kernel.org
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com,
        roberto.sassu@...wei.com, nramas@...ux.microsoft.com,
        eric.snowberg@...cle.com, pvorel@...e.cz, tiwai@...e.de,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: [PATCH 2/7] KEYS: 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 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@...cle.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 2899ed80bb18..30f7374ea9c0 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 (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->is_root_ca = true;
+	}
+
 	return 0;
 }
 
diff --git a/crypto/asymmetric_keys/x509_parser.h b/crypto/asymmetric_keys/x509_parser.h
index 97a886cbe01c..dc45df9f6594 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		is_root_ca;		/* T if basic constraints CA is set */
 };
 
 /*
-- 
2.27.0