rngd_linux.c

/*
 * rngd_linux.c -- Entropy sink for the Linux Kernel (/dev/random)
 *
 * Copyright (C) 2001 Philipp Rumpf
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA  02110-1335  USA
 */

#define _GNU_SOURCE

#ifndef HAVE_CONFIG_H
#error Invalid or missing autoconf build environment
#endif

#include "rng-tools-config.h"

#include <unistd.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <syslog.h>
#include <sys/ioctl.h>
#include <sys/poll.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/time.h>
#include <time.h>
#include <linux/types.h>
#include <linux/random.h>
#include <string.h>

#include "rngd.h"
#include "fips.h"
#include "exits.h"
#include "rngd_linux.h"

/* Kernel output device */
static int random_fd;

extern int kent_pool_size;

/*
 * Initialize the interface to the Linux Kernel
 * entropy pool (through /dev/random)
 *
 * randomdev is the path to the random device
 */

#define DEFAULT_WATERMARK_GUESS 256

void init_kernel_rng(const char* randomdev)
{
	FILE *f;
	int err;
	unsigned int wm;

	/* Try to open and read poolsize sysfs file */
	f = fopen("/proc/sys/kernel/random/poolsize", "r");
	if (!f) {
		wm = DEFAULT_WATERMARK_GUESS;
		message(LOG_DAEMON|LOG_WARNING,
			"can't open /proc/sys/kernel/random/poolsize: %s\n",
			strerror(errno));
		goto err;
	}

	/* Use DEFAULT_WATERMARK_GUESS if fscanf fails */
	if(fscanf(f,"%u", &wm) < 1) {
		wm = DEFAULT_WATERMARK_GUESS;
		message(LOG_DAEMON|LOG_WARNING,
			"can't read /proc/sys/kernel/random/poolsize: %s\n",
			strerror(errno));
	}
	fclose(f);

err:
	/* Set the fill_watermark to wm if it was not set on a command line */
	kent_pool_size = wm;
	wm = wm*3/4;
	if (arguments->fill_watermark == -1)
		arguments->fill_watermark = wm;

	/* Try to open randomdev file for writing */
	random_fd = open(randomdev, O_RDWR);
	if (random_fd == -1) {
		message(LOG_DAEMON|LOG_ERR, "can't open %s: %s",
			randomdev, strerror(errno));
		exit(EXIT_USAGE);
	}

	/* Don't set the watermark if the watermark is zero */
	if (!arguments->fill_watermark) {
		message(LOG_DAEMON|LOG_DEBUG,
			"Kernel entropy pool size %d, pool watermark is not set\n",
			kent_pool_size);
		return;
	}

	/* Actually set entropy pool watermark */
	f = fopen("/proc/sys/kernel/random/write_wakeup_threshold", "w");
	if (!f) {
		err = 1;
	} else {
		fprintf(f, "%d\n", arguments->fill_watermark);
		/* Note | not || here... we always want to close the file */
		err = ferror(f) | fclose(f);
	}
	if (err)
		message(LOG_DAEMON|LOG_WARNING,
			"unable to adjust write_wakeup_threshold: %s\n",
			strerror(errno));
	else
		message(LOG_DAEMON|LOG_DEBUG,
			"Kernel entropy pool size %d, pool watermark %d\n",
			kent_pool_size, arguments->fill_watermark);
}

struct entropy {
	int ent_count;
	int size;
};

int random_add_entropy(void *buf, size_t size)
{
	static bool write_to_output = false;

	struct entropy *ent = alloca(sizeof(struct entropy) + size);

	ent->ent_count = size * arguments->entropy_count;
	ent->size = size;
	memcpy(ent + 1, buf, size);

	if (write_to_output == false) {
		if (ioctl(random_fd, RNDADDENTROPY, ent) < 0) {
			if (errno == ENOTTY && !arguments->daemon) {
				/*
				 * This isn't a real random device.
				 * Switch to plain output if we are in
				 * foreground
				 */
				write_to_output = true;
			} else {
				message(LOG_DAEMON|LOG_ERR, "RNDADDENTROPY failed: %s\n",
					strerror(errno));
				return -1;
			}

		} else {
			if (ioctl(random_fd, RNDGETENTCNT, &ent->ent_count) != 0) {
				message(LOG_DAEMON|LOG_ERR, "Failed to get Entropy count!\n");
				ent->ent_count = 0;
			}
		}
	} else
		write(random_fd, buf, size);

	return ent->ent_count;

}

void random_sleep(void)
{
	struct pollfd pfd = {
		.fd = random_fd,
		.events = POLLOUT,
	};

	poll(&pfd, 1, -1);
}