integrity: convert digsig to akcipher api

BugLink: http://bugs.launchpad.net/bugs/1735977

Convert asymmetric_verify to akcipher api.
Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David Howells <dhowells@redhat.com>
(cherry picked from commit eb5798f2)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

security/integrity/Kconfig

@@ -36,6 +36,7 @@ config INTEGRITY_ASYMMETRIC_KEYS
         select ASYMMETRIC_KEY_TYPE
         select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
         select PUBLIC_KEY_ALGO_RSA
+        select CRYPTO_RSA
         select X509_CERTIFICATE_PARSER
 	help
 	  This option enables digital signature verification using

security/integrity/digsig_asymmetric.c

@@ -106,13 +106,9 @@ int asymmetric_verify(struct key *keyring, const char *sig,
 	pks.pkey_hash_algo = hdr->hash_algo;
 	pks.digest = (u8 *)data;
 	pks.digest_size = datalen;
-	pks.nr_mpi = 1;
-	pks.rsa.s = mpi_read_raw_data(hdr->sig, siglen);
-
-	if (pks.rsa.s)
-		ret = verify_signature(key, &pks);
-
-	mpi_free(pks.rsa.s);
+	pks.s = hdr->sig;
+	pks.s_size = siglen;
+	ret = verify_signature(key, &pks);
 	key_put(key);
 	pr_debug("%s() = %d\n", __func__, ret);
 	return ret;