--- x/drivers/char/hw_random/core.c
+++ y/drivers/char/hw_random/core.c
@@ -213,6 +213,7 @@ static ssize_t rng_dev_read(struct file
 	int err = 0;
 	int bytes_read, len;
 	struct hwrng *rng;
+	char rnd[32];
 
 	while (size) {
 		rng = get_current_rng();
@@ -245,24 +246,28 @@ static ssize_t rng_dev_read(struct file
 				err = -EAGAIN;
 				goto out_unlock_reading;
 			}
+			mutex_unlock(&reading_mutex);
 		} else {
 			len = data_avail;
 			if (len > size)
 				len = size;
+			if (len > 32)
+				len = 32;
 
 			data_avail -= len;
 
-			if (copy_to_user(buf + ret, rng_buffer + data_avail,
-								len)) {
+			memcpy(rnd, rng_buffer + data_avail, len);
+			mutex_unlock(&reading_mutex);
+
+			if (copy_to_user(buf + ret, rnd, len)) {
 				err = -EFAULT;
-				goto out_unlock_reading;
+				goto out_put;
 			}
 
 			size -= len;
 			ret += len;
 		}
 
-		mutex_unlock(&reading_mutex);
 		put_rng(rng);
 
 		if (need_resched())