virtio-crypto: adjust dst_len at ops callback

For some akcipher operations(eg, decryption of pkcs1pad(rsa)),
the length of returned result maybe less than akcipher_req->dst_len,
we need to recalculate the actual dst_len through the virt-queue
protocol.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Gonglei <arei.gonglei@huawei.com>
Reviewed-by: Gonglei <arei.gonglei@huawei.com>
Signed-off-by: lei he <helei.sig11@bytedance.com>
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
Message-Id: <20220506131627.180784-5-pizhenwei@bytedance.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/crypto/virtio/virtio_crypto_akcipher_algs.c

@@ -90,9 +90,12 @@ static void virtio_crypto_dataq_akcipher_callback(struct virtio_crypto_request *
 	}
 
 	akcipher_req = vc_akcipher_req->akcipher_req;
-	if (vc_akcipher_req->opcode != VIRTIO_CRYPTO_AKCIPHER_VERIFY)
+	if (vc_akcipher_req->opcode != VIRTIO_CRYPTO_AKCIPHER_VERIFY) {
+		/* actuall length maybe less than dst buffer */
+		akcipher_req->dst_len = len - sizeof(vc_req->status);
 		sg_copy_from_buffer(akcipher_req->dst, sg_nents(akcipher_req->dst),
 				    vc_akcipher_req->dst_buf, akcipher_req->dst_len);
+	}
 	virtio_crypto_akcipher_finalize_req(vc_akcipher_req, akcipher_req, error);
 }