crypto: rsa-pkcs1pad: Allow hash to be optional [ver #2]

The original pkcs1pad implementation allowed to pad/unpad raw RSA
output.  However, this has been taken out in commit:
commit c0d20d22e0ad ("crypto: rsa-pkcs1pad - Require hash to be present")

This patch restored this ability as it is needed by the asymmetric key
implementation.

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: James Morris <james.morris@microsoft.com>

crypto/rsa-pkcs1pad.c

@@ -392,7 +392,8 @@ static int pkcs1pad_sign(struct akcipher_request *req)
 	if (!ctx->key_size)
 		return -EINVAL;
 
-	digest_size = digest_info->size;
+	if (digest_info)
+		digest_size = digest_info->size;
 
 	if (req->src_len + digest_size > ctx->key_size - 11)
 		return -EOVERFLOW;
@@ -412,8 +413,9 @@ static int pkcs1pad_sign(struct akcipher_request *req)
 	memset(req_ctx->in_buf + 1, 0xff, ps_end - 1);
 	req_ctx->in_buf[ps_end] = 0x00;
 
-	memcpy(req_ctx->in_buf + ps_end + 1, digest_info->data,
-	       digest_info->size);
+	if (digest_info)
+		memcpy(req_ctx->in_buf + ps_end + 1, digest_info->data,
+		       digest_info->size);
 
 	pkcs1pad_sg_set_buf(req_ctx->in_sg, req_ctx->in_buf,
 			ctx->key_size - 1 - req->src_len, req->src);
@@ -475,10 +477,13 @@ static int pkcs1pad_verify_complete(struct akcipher_request *req, int err)
 		goto done;
 	pos++;
 
-	if (crypto_memneq(out_buf + pos, digest_info->data, digest_info->size))
-		goto done;
+	if (digest_info) {
+		if (crypto_memneq(out_buf + pos, digest_info->data,
+				  digest_info->size))
+			goto done;
 
-	pos += digest_info->size;
+		pos += digest_info->size;
+	}
 
 	err = 0;
 
@@ -608,11 +613,14 @@ static int pkcs1pad_create(struct crypto_template *tmpl, struct rtattr **tb)
 
 	hash_name = crypto_attr_alg_name(tb[2]);
 	if (IS_ERR(hash_name))
-		return PTR_ERR(hash_name);
+		hash_name = NULL;
 
-	digest_info = rsa_lookup_asn1(hash_name);
-	if (!digest_info)
-		return -EINVAL;
+	if (hash_name) {
+		digest_info = rsa_lookup_asn1(hash_name);
+		if (!digest_info)
+			return -EINVAL;
+	} else
+		digest_info = NULL;
 
 	inst = kzalloc(sizeof(*inst) + sizeof(*ctx), GFP_KERNEL);
 	if (!inst)
@@ -632,14 +640,29 @@ static int pkcs1pad_create(struct crypto_template *tmpl, struct rtattr **tb)
 
 	err = -ENAMETOOLONG;
 
-	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
-		     "pkcs1pad(%s,%s)", rsa_alg->base.cra_name, hash_name) >=
-	    CRYPTO_MAX_ALG_NAME ||
-	    snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
-		     "pkcs1pad(%s,%s)",
-		     rsa_alg->base.cra_driver_name, hash_name) >=
-	    CRYPTO_MAX_ALG_NAME)
-		goto out_drop_alg;
+	if (!hash_name) {
+		if (snprintf(inst->alg.base.cra_name,
+			     CRYPTO_MAX_ALG_NAME, "pkcs1pad(%s)",
+			     rsa_alg->base.cra_name) >= CRYPTO_MAX_ALG_NAME)
+			goto out_drop_alg;
+
+		if (snprintf(inst->alg.base.cra_driver_name,
+			     CRYPTO_MAX_ALG_NAME, "pkcs1pad(%s)",
+			     rsa_alg->base.cra_driver_name) >=
+			     CRYPTO_MAX_ALG_NAME)
+			goto out_drop_alg;
+	} else {
+		if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
+			     "pkcs1pad(%s,%s)", rsa_alg->base.cra_name,
+			     hash_name) >= CRYPTO_MAX_ALG_NAME)
+			goto out_drop_alg;
+
+		if (snprintf(inst->alg.base.cra_driver_name,
+			     CRYPTO_MAX_ALG_NAME, "pkcs1pad(%s,%s)",
+			     rsa_alg->base.cra_driver_name,
+			     hash_name) >= CRYPTO_MAX_ALG_NAME)
+			goto out_drop_alg;
+	}
 
 	inst->alg.base.cra_flags = rsa_alg->base.cra_flags & CRYPTO_ALG_ASYNC;
 	inst->alg.base.cra_priority = rsa_alg->base.cra_priority;