[PATCH 3/5] tlshd: Make sure x509.pq.certificate is using a PQ public-key alg

[Scott Mayhew <smayhew@redhat.com>]

Ensure that the PQ certificate is using a post-quantum public-key
algorithm (ML-DSA-44, ML-DSA-65, or ML-DSA-87).

Link: https://github.com/oracle/ktls-utils/issues/113
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
---
 src/tlshd/config.c       | 53 +++++++++++++++++++++++++++++++++++++++-
 src/tlshd/server.c       |  6 +++--
 src/tlshd/tlshd.conf.man |  2 ++
 src/tlshd/tlshd.h        |  3 ++-
 4 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/src/tlshd/config.c b/src/tlshd/config.c
index 20634dd..6adacc0 100644
--- a/src/tlshd/config.c
+++ b/src/tlshd/config.c
@@ -401,11 +401,47 @@ bool tlshd_config_get_server_crl(char **result)
 	return true;
 }
 
+#ifdef HAVE_GNUTLS_MLDSA
+static bool tlshd_cert_check_pk_alg(gnutls_datum_t *data)
+{
+	gnutls_x509_crt_t cert;
+	gnutls_pk_algorithm_t pk_alg;
+	int ret;
+
+	ret = gnutls_x509_crt_init(&cert);
+	if (ret < 0)
+		return false;
+
+	ret = gnutls_x509_crt_import(cert, data, GNUTLS_X509_FMT_PEM);
+	if (ret < 0) {
+		gnutls_x509_crt_deinit(cert);
+		return false;
+	}
+
+	pk_alg = gnutls_x509_crt_get_pk_algorithm(cert, NULL);
+	tlshd_log_debug("%s: certificate pk algorithm %s", __func__,
+			gnutls_pk_algorithm_get_name(pk_alg));
+	switch (pk_alg) {
+	case GNUTLS_PK_MLDSA44:
+	case GNUTLS_PK_MLDSA65:
+	case GNUTLS_PK_MLDSA87:
+		break;
+	default:
+		gnutls_x509_crt_deinit(cert);
+		return false;
+	}
+
+	gnutls_x509_crt_deinit(cert);
+	return true;
+}
+#endif /* HAVE_GNUTLS_MLDSA */
+
 /**
  * tlshd_config_get_server_certs - Get certs for ServerHello from .conf
  * @key: IN: the key field name from .conf
  * @certs: OUT: in-memory certificates
  * @certs_len: IN: maximum number of certs to get, OUT: number of certs found
+ * @check_pq: IN: verify that the cert is using a PQ public-key alg
  *
  * Return values:
  *   %true: certificate retrieved successfully
@@ -413,8 +449,12 @@ bool tlshd_config_get_server_crl(char **result)
  */
 bool tlshd_config_get_server_certs(const gchar *key,
 				   gnutls_pcert_st *certs,
-				   unsigned int *certs_len)
+				   unsigned int *certs_len,
+				   bool check_pq)
 {
+#ifndef HAVE_GNUTLS_MLSDA
+	(void)check_pq;
+#endif /* HAVE_GNUTLS_MLDSA */
 	gnutls_datum_t data;
 	gchar *pathname;
 	int ret;
@@ -430,6 +470,17 @@ bool tlshd_config_get_server_certs(const gchar *key,
 		return false;
 	}
 
+#ifdef HAVE_GNUTLS_MLDSA
+	if (check_pq && !tlshd_cert_check_pk_alg(&data)) {
+		tlshd_log_debug("%s: %s certificate not using a PQ public-key algorithm",
+				__func__, key);
+		free(data.data);
+		g_free(pathname);
+		*certs_len = 0;
+		return false;
+	}
+#endif /* HAVE_GNUTLS_MLDSA */
+
 	/* Config file supports only PEM-encoded certificates */
 	ret = gnutls_pcert_list_import_x509_raw(certs, certs_len, &data,
 						GNUTLS_X509_FMT_PEM, 0);
diff --git a/src/tlshd/server.c b/src/tlshd/server.c
index 96b1b88..210a09e 100644
--- a/src/tlshd/server.c
+++ b/src/tlshd/server.c
@@ -61,11 +61,13 @@ static bool tlshd_x509_server_get_certs(struct tlshd_handshake_parms *parms)
 #ifdef HAVE_GNUTLS_MLDSA
 	tlshd_config_get_server_certs("x509.pq.certificate",
 				      tlshd_server_pq_certs,
-				      &tlshd_server_pq_certs_len);
+				      &tlshd_server_pq_certs_len,
+				      true);
 #endif /* HAVE_GNUTLS_MLDSA */
 	return tlshd_config_get_server_certs("x509.certificate",
 					     tlshd_server_certs,
-					     &tlshd_server_certs_len);
+					     &tlshd_server_certs_len,
+					     false);
 }
 
 static void tlshd_x509_server_put_certs(void)
diff --git a/src/tlshd/tlshd.conf.man b/src/tlshd/tlshd.conf.man
index ed545e4..575d88b 100644
--- a/src/tlshd/tlshd.conf.man
+++ b/src/tlshd/tlshd.conf.man
@@ -130,6 +130,8 @@ a PEM-encoded private key associated with the above certificate.
 This option specifies the pathname of a file containing
 a PEM-encoded x.509 certificate that is to be presented during
 a handshake request if the peer supports post-quantum cryptography.
+This certificate must be using a post-quantum public-key algorithm
+(ML-DSA-44, ML-DSA-65, or ML-DSA-87).
 If the peer does not support post-quantum cryptography, the
 certificate configured in the
 .I x509.certificate
diff --git a/src/tlshd/tlshd.h b/src/tlshd/tlshd.h
index d9b68ed..6bd55c7 100644
--- a/src/tlshd/tlshd.h
+++ b/src/tlshd/tlshd.h
@@ -61,7 +61,8 @@ bool tlshd_config_get_server_truststore(char **bundle);
 bool tlshd_config_get_server_crl(char **result);
 bool tlshd_config_get_server_certs(const gchar *key,
 				   gnutls_pcert_st *certs,
-				   unsigned int *certs_len);
+				   unsigned int *certs_len,
+				   bool check_pq);
 bool tlshd_config_get_server_privkey(const gchar *key,
 				     gnutls_privkey_t *privkey);
 
-- 
2.50.1