int aws_nitro_enclaves_library_seed_entropy()

in source/nitro_enclaves.c [61:110]

• 36 lines of code
• 9 McCabe index (conditional complexity)

int aws_nitro_enclaves_library_seed_entropy(uint64_t num_bytes) {

    int nsm_fd = nsm_lib_init();
    if (nsm_fd < 0) {
        return AWS_OP_ERR;
    }

    int dev_fd = open("/dev/random", O_WRONLY);
    if (dev_fd < 0) {
        nsm_lib_exit(nsm_fd);
        return AWS_OP_ERR;
    }

    uint64_t count = 0;

    while (count != num_bytes) {
        uint8_t buf[NSM_RANDOM_REQ_SIZE];
        size_t buf_len = sizeof(buf) > (num_bytes - count) ? (num_bytes - count) : sizeof(buf);

        /* Yields up to 256 bytes */
        int rc = nsm_get_random(nsm_fd, buf, &buf_len);
        if (rc)
            goto err;

        if (buf_len == 0) {
            /* NSM starts yielding zero entropy */
            goto err;
        }

        if ((ssize_t)buf_len != write(dev_fd, buf, buf_len))
            goto err;

        int bits = buf_len * 8;
        rc = ioctl(dev_fd, RNDADDTOENTCNT, &bits);
        if (rc < 0)
            goto err;

        count += buf_len;
    }

    close(dev_fd);
    nsm_lib_exit(nsm_fd);

    return AWS_OP_SUCCESS;
err:
    close(dev_fd);
    nsm_lib_exit(nsm_fd);

    return AWS_OP_ERR;
}