pkcs7: Allow authenticatedAttributes for ML-DSA

Allow the rejection of authenticatedAttributes in PKCS#7 (signedAttrs in
CMS) to be waived in the kernel config for ML-DSA when used for module
signing.  This reflects the issue that openssl < 4.0 cannot do this and
openssl-4 has not yet been released.

This does not permit RSA, ECDSA or ECRDSA to be so waived (behaviour
unchanged).

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Lukas Wunner <lukas@wunner.de>
cc: Ignat Korchagin <ignat@cloudflare.com>
cc: Jarkko Sakkinen <jarkko@kernel.org>
cc: Stephan Mueller <smueller@chronox.de>
cc: Eric Biggers <ebiggers@kernel.org>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: keyrings@vger.kernel.org
cc: linux-crypto@vger.kernel.org

Author: dhowells

crypto/asymmetric_keys/Kconfig

@@ -53,6 +53,17 @@ config PKCS7_MESSAGE_PARSER
 	  This option provides support for parsing PKCS#7 format messages for
 	  signature data and provides the ability to verify the signature.
 
+config PKCS7_WAIVE_AUTHATTRS_REJECTION_FOR_MLDSA
+	bool "Waive rejection of authenticatedAttributes for ML-DSA"
+	depends on PKCS7_MESSAGE_PARSER
+	depends on CRYPTO_MLDSA
+	help
+	  Due to use of CMS_NOATTR with ML-DSA not being supported in
+	  OpenSSL < 4.0 (and thus any released version), enabling this
+	  allows authenticatedAttributes to be used with ML-DSA for
+	  module signing.  Use of authenticatedAttributes in this
+	  context is normally rejected.
+
 config PKCS7_TEST_KEY
 	tristate "PKCS#7 testing key type"
 	depends on SYSTEM_DATA_VERIFICATION

crypto/asymmetric_keys/pkcs7_parser.c

@@ -92,9 +92,17 @@ static int pkcs7_check_authattrs(struct pkcs7_message *msg)
 	if (!sinfo)
 		goto inconsistent;
 
+#ifdef CONFIG_PKCS7_WAIVE_AUTHATTRS_REJECTION_FOR_MLDSA
+	msg->authattrs_rej_waivable = true;
+#endif
+
 	if (sinfo->authattrs) {
 		want = true;
 		msg->have_authattrs = true;
+#ifdef CONFIG_PKCS7_WAIVE_AUTHATTRS_REJECTION_FOR_MLDSA
+		if (strncmp(sinfo->sig->pkey_algo, "mldsa", 5) != 0)
+			msg->authattrs_rej_waivable = false;
+#endif
 	} else if (sinfo->sig->algo_takes_data) {
 		sinfo->sig->hash_algo = "none";
 	}

crypto/asymmetric_keys/pkcs7_parser.h

@@ -55,6 +55,9 @@ struct pkcs7_message {
 	struct pkcs7_signed_info *signed_infos;
 	u8		version;	/* Version of cert (1 -> PKCS#7 or CMS; 3 -> CMS) */
 	bool		have_authattrs;	/* T if have authattrs */
+#ifdef CONFIG_PKCS7_WAIVE_AUTHATTRS_REJECTION_FOR_MLDSA
+	bool		authattrs_rej_waivable; /* T if authatts rejection can be waived */
+#endif
 
 	/* Content Data (or NULL) */
 	enum OID	data_type;	/* Type of Data */

crypto/asymmetric_keys/pkcs7_verify.c

@@ -425,6 +425,12 @@ int pkcs7_verify(struct pkcs7_message *pkcs7,
 			return -EKEYREJECTED;
 		}
 		if (pkcs7->have_authattrs) {
+#ifdef CONFIG_PKCS7_WAIVE_AUTHATTRS_REJECTION_FOR_MLDSA
+			if (pkcs7->authattrs_rej_waivable) {
+				pr_warn("Waived invalid module sig (has authattrs)\n");
+				break;
+			}
+#endif
 			pr_warn("Invalid module sig (has authattrs)\n");
 			return -EKEYREJECTED;
 		}