x509: Separately calculate sha256 for blacklist

Calculate the SHA256 hash for blacklisting purposes independently of the
signature hash (which may be something other than SHA256).

This is necessary because when ML-DSA is used, no digest is calculated.

Note that this represents a change of behaviour in that the hash used for
the blacklist check would previously have been whatever digest was used
for, say, RSA-based signatures.  It may be that this is inadvisable.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
cc: Lukas Wunner <lukas@wunner.de>
cc: Ignat Korchagin <ignat@cloudflare.com>
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/x509_parser.h

@@ -9,12 +9,14 @@
 #include <linux/time.h>
 #include <crypto/public_key.h>
 #include <keys/asymmetric-type.h>
+#include <crypto/sha2.h>
 
 struct x509_certificate {
 	struct x509_certificate *next;
 	struct x509_certificate *signer;	/* Certificate that signed this one */
 	struct public_key *pub;			/* Public key details */
 	struct public_key_signature *sig;	/* Signature parameters */
+	u8		sha256[SHA256_DIGEST_SIZE]; /* Hash for blacklist purposes */
 	char		*issuer;		/* Name of certificate issuer */
 	char		*subject;		/* Name of certificate subject */
 	struct asymmetric_key_id *id;		/* Issuer + Serial number */

crypto/asymmetric_keys/x509_public_key.c

@@ -31,6 +31,19 @@ int x509_get_sig_params(struct x509_certificate *cert)
 
 	pr_devel("==>%s()\n", __func__);
 
+	/* Calculate a SHA256 hash of the TBS and check it against the
+	 * blacklist.
+	 */
+	sha256(cert->tbs, cert->tbs_size, cert->sha256);
+	ret = is_hash_blacklisted(cert->sha256, sizeof(cert->sha256),
+				  BLACKLIST_HASH_X509_TBS);
+	if (ret == -EKEYREJECTED) {
+		pr_err("Cert %*phN is blacklisted\n",
+		       (int)sizeof(cert->sha256), cert->sha256);
+		cert->blacklisted = true;
+		ret = 0;
+	}
+
 	sig->s = kmemdup(cert->raw_sig, cert->raw_sig_size, GFP_KERNEL);
 	if (!sig->s)
 		return -ENOMEM;
@@ -69,15 +82,6 @@ int x509_get_sig_params(struct x509_certificate *cert)
 	if (ret < 0)
 		goto error_2;
 
-	ret = is_hash_blacklisted(sig->digest, sig->digest_size,
-				  BLACKLIST_HASH_X509_TBS);
-	if (ret == -EKEYREJECTED) {
-		pr_err("Cert %*phN is blacklisted\n",
-		       sig->digest_size, sig->digest);
-		cert->blacklisted = true;
-		ret = 0;
-	}
-
 error_2:
 	kfree(desc);
 error: