/*
    * Non-physical true random number generator based on timing jitter.
    *
    * Copyright Stephan Mueller <smueller@chronox.de>, 2014
    * Copyright Petr Štetiar <ynezz@true.cz>, 2019
    *
    * Redistribution and use in source and binary forms, with or without
    * modification, are permitted provided that the following conditions
    * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, and the entire permission notice in its entirety,
   *    including the disclaimer of warranties.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. The name of the author may not be used to endorse or promote
   *    products derived from this software without specific prior
   *    written permission.
   *
   * ALTERNATIVELY, this product may be distributed under the terms of
   * the GNU General Public License, in which case the provisions of the GPL are
   * required INSTEAD OF the above restrictions.  (This clause is
   * necessary due to a potential bad interaction between the GPL and
   * the restrictions contained in a BSD-style copyright.)
   *
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
   * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
   * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
   * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
   * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
   * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
   * DAMAGE.
   */
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  
  #include <sys/ioctl.h>
  #include <linux/random.h>
  
  #include <libubox/uloop.h>
  
  #include "log.h"
  #include "jitterentropy.h"
  
  #define ENTROPYBYTES 32
  #define ENTROPYTHRESH 1024
  #define OVERSAMPLINGFACTOR 2
  #define DEV_RANDOM "/dev/random"
  #define ENTROPYAVAIL "/proc/sys/kernel/random/entropy_avail"
  #define ENTROPYPOOLBYTES (sizeof(struct rand_pool_info) + \
                  (ENTROPYBYTES * OVERSAMPLINGFACTOR * sizeof(char)))
  
  #ifdef URNGD_DEBUG
  unsigned int debug;
  #endif
  
  struct urngd {
          struct uloop_fd rnd_fd;
          struct rand_data *ec;
          struct rand_pool_info *rpi;
  };
  
  static struct urngd urngd_service;
  
  static inline void memset_secure(void *s, int c, size_t n)
  {
          memset(s, c, n);
          __asm__ __volatile__("" : : "r" (s) : "memory");
  }
  
  static size_t write_entropy(struct urngd *u, char *buf, size_t len,
                              size_t entropy_bytes)
  {
          int ret;
          size_t written = 0;
  
          /* value is in bits */
          u->rpi->entropy_count = (entropy_bytes * 8);
          u->rpi->buf_size = len;
          memcpy(u->rpi->buf, buf, len);
          memset(buf, 0, len);
  
          ret =  ioctl(u->rnd_fd.fd, RNDADDENTROPY, u->rpi);
          if (0 > ret) {
                  ERROR("error injecting entropy: %s\n", strerror(errno));
          } else {
                  DEBUG(1, "injected %zub (%zub of entropy)\n", len, entropy_bytes);
                  written = len;
          }
  
          u->rpi->entropy_count = 0;
          u->rpi->buf_size = 0;
         memset(u->rpi->buf, 0, len);
 
         return written;
 }
 
 static size_t gather_entropy(struct urngd *u)
 {
         size_t ret = 0;
         char buf[(ENTROPYBYTES * OVERSAMPLINGFACTOR)];
 
         if (jent_read_entropy(u->ec, buf, sizeof(buf)) < 0) {
                 ERROR("cannot read entropy\n");
                 return 0;
         }
 
         ret = write_entropy(u, buf, sizeof(buf), ENTROPYBYTES);
         if (sizeof(buf) != ret) {
                 ERROR("injected %zub of entropy, less then %zub expected\n",
                       ret, sizeof(buf));
         } else {
                 ret = sizeof(buf);
         }
 
         memset_secure(buf, 0, sizeof(buf));
         DEBUG(2, DEV_RANDOM " fed with %zub of entropy\n", ret);
 
         return ret;
 }
 
 static void low_entropy_cb(struct uloop_fd *ufd, unsigned int events)
 {
         struct urngd *u = container_of(ufd, struct urngd, rnd_fd);
 
         DEBUG(2, DEV_RANDOM " signals low entropy\n");
         gather_entropy(u);
 }
 
 static void urngd_done(struct urngd *u)
 {
         if (u->ec) {
                 jent_entropy_collector_free(u->ec);
                 u->ec = NULL;
         }
 
         if (u->rpi) {
                 memset(u->rpi, 0, ENTROPYPOOLBYTES);
                 free(u->rpi);
                 u->rpi = NULL;
         }
 
         if (u->rnd_fd.fd) {
                 close(u->rnd_fd.fd);
                 u->rnd_fd.fd = 0;
         }
 }
 
 static bool urngd_init(struct urngd *u)
 {
         int ret = jent_entropy_init();
         if (ret) {
                 ERROR("jent-rng init failed, err: %d\n", ret);
                 return false;
         }
 
         u->ec = jent_entropy_collector_alloc(1, 0);
         if (!u->ec) {
                 ERROR("jent-rng alloc failed\n");
                 return false;
         }
 
         u->rpi = malloc(ENTROPYPOOLBYTES);
         if (!u->rpi) {
                 ERROR("rand pool alloc failed\n");
                 return false;
         }
 
         u->rnd_fd.cb = low_entropy_cb;
         u->rnd_fd.fd = open(DEV_RANDOM, O_WRONLY);
         if (u->rnd_fd.fd < 1) {
                 ERROR(DEV_RANDOM " open failed: %s\n", strerror(errno));
                 return false;
         }
 
         uloop_fd_add(&u->rnd_fd, ULOOP_WRITE);
 
         return true;
 }
 
 static int usage(const char *prog)
 {
         fprintf(stderr, "Usage: %s [options]\n"
                 "Options:\n"
 #ifdef URNGD_DEBUG
                 "       -d <level>      Enable debug messages\n"
 #endif
                 "       -S              Print messages to stdout\n"
                 "\n", prog);
         return 1;
 }
 
 int main(int argc, char **argv)
 {
         int ch;
         int ulog_channels = ULOG_KMSG;
 #ifdef URNGD_DEBUG
         char *dbglvl = getenv("DBGLVL");
 
         if (dbglvl) {
                 debug = atoi(dbglvl);
                 unsetenv("DBGLVL");
         }
 #endif
 
         while ((ch = getopt(argc, argv, "d:S")) != -1) {
                 switch (ch) {
 #ifdef URNGD_DEBUG
                 case 'd':
                         debug = atoi(optarg);
                         break;
 #endif
                 case 'S':
                         ulog_channels = ULOG_STDIO;
                         break;
                 default:
                         return usage(argv[0]);
                 }
         }
 
         ulog_open(ulog_channels, LOG_DAEMON, "urngd");
 
         uloop_init();
         if (!urngd_init(&urngd_service)) {
                 uloop_done();
                 return -1;
         }
 
         LOG("v%s started.\n", URNGD_VERSION);
 
         gather_entropy(&urngd_service);
 
         uloop_run();
         uloop_done();
 
         urngd_done(&urngd_service);
 
         return 0;
 }
 

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