KEYS: Split public_key_verify_signature() and make available

Modify public_key_verify_signature() so that it now takes a public_key struct
rather than a key struct and supply a wrapper that takes a key struct.  The
wrapper is then used by the asymmetric key subtype and the modified function is
used by X.509 self-signature checking and can be used by other things also.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Josh Boyer <jwboyer@redhat.com>

crypto/asymmetric_keys/public_key.c

@@ -86,21 +86,45 @@ EXPORT_SYMBOL_GPL(public_key_destroy);
 /*
  * Verify a signature using a public key.
  */
-static int public_key_verify_signature(const struct key *key,
+int public_key_verify_signature(const struct public_key *pk,
 				const struct public_key_signature *sig)
 {
-	const struct public_key *pk = key->payload.data;
+	const struct public_key_algorithm *algo;
+
+	BUG_ON(!pk);
+	BUG_ON(!pk->mpi[0]);
+	BUG_ON(!pk->mpi[1]);
+	BUG_ON(!sig);
+	BUG_ON(!sig->digest);
+	BUG_ON(!sig->mpi[0]);
 
-	if (!pk->algo->verify_signature)
+	algo = pk->algo;
+	if (!algo) {
+		if (pk->pkey_algo >= PKEY_ALGO__LAST)
+			return -ENOPKG;
+		algo = pkey_algo[pk->pkey_algo];
+		if (!algo)
+			return -ENOPKG;
+	}
+
+	if (!algo->verify_signature)
 		return -ENOTSUPP;
 
-	if (sig->nr_mpi != pk->algo->n_sig_mpi) {
+	if (sig->nr_mpi != algo->n_sig_mpi) {
 		pr_debug("Signature has %u MPI not %u\n",
-			 sig->nr_mpi, pk->algo->n_sig_mpi);
+			 sig->nr_mpi, algo->n_sig_mpi);
 		return -EINVAL;
 	}
 
-	return pk->algo->verify_signature(pk, sig);
+	return algo->verify_signature(pk, sig);
+}
+EXPORT_SYMBOL_GPL(public_key_verify_signature);
+
+static int public_key_verify_signature_2(const struct key *key,
+					 const struct public_key_signature *sig)
+{
+	const struct public_key *pk = key->payload.data;
+	return public_key_verify_signature(pk, sig);
 }
 
 /*
@@ -111,6 +135,6 @@ struct asymmetric_key_subtype public_key_subtype = {
 	.name			= "public_key",
 	.describe		= public_key_describe,
 	.destroy		= public_key_destroy,
-	.verify_signature	= public_key_verify_signature,
+	.verify_signature	= public_key_verify_signature_2,
 };
 EXPORT_SYMBOL_GPL(public_key_subtype);

crypto/asymmetric_keys/public_key.h

@@ -28,3 +28,9 @@ struct public_key_algorithm {
 };
 
 extern const struct public_key_algorithm RSA_public_key_algorithm;
+
+/*
+ * public_key.c
+ */
+extern int public_key_verify_signature(const struct public_key *pk,
+				       const struct public_key_signature *sig);

crypto/asymmetric_keys/x509_public_key.c

@@ -76,7 +76,7 @@ static int x509_check_signature(const struct public_key *pub,
 	if (ret < 0)
 		goto error_mpi;
 
-	ret = pub->algo->verify_signature(pub, sig);
+	ret = public_key_verify_signature(pub, sig);
 
 	pr_debug("Cert Verification: %d\n", ret);