rand/noise.c (noise_devrandom): Refactor internals.

[catacomb] / rand / noise.c

/* -*-c-*-
 *
 * Acquisition of environmental noise (Unix-specific)
 *
 * (c) 1998 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * Catacomb 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 Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

#include "config.h"

#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <sys/types.h>
#include <sys/time.h>
#include <sys/wait.h>

#include <fcntl.h>
#include <unistd.h>

#ifdef HAVE_SETGROUPS
#  include <grp.h>
#endif

#include <mLib/bits.h>
#include <mLib/mdup.h>
#include <mLib/sel.h>
#include <mLib/tv.h>

#include "noise.h"
#include "paranoia.h"
#include "rand.h"

/*----- Magical numbers ---------------------------------------------------*/

#define NOISE_KIDLIFE 100000		/* @noise_filter@ child lifetime */
#define MILLION 1000000			/* One million */

/*----- Noise source definition -------------------------------------------*/

const rand_source noise_source = { noise_acquire, noise_timer };

/*----- Static variables --------------------------------------------------*/

/* --- Timer differences --- */

static unsigned long noise_last;	/* Last time recorded */
static unsigned long noise_diff;	/* Last first order difference */

/* --- Setuid program handling --- */

static uid_t noise_uid = NOISE_NOSETUID; /* Uid to set to spawn processes */
static gid_t noise_gid = NOISE_NOSETGID; /* Gid to set to spawn processes */

/*----- Main code ---------------------------------------------------------*/

/* --- @bitcount@ --- *
 *
 * Arguments:	@unsigned long x@ = a word containing bits
 *
 * Returns:	The number of bits set in the word.
 */

static int bitcount(unsigned long x)
{
  static const char ctab[] = { 0, 1, 1, 2, 1, 2, 2, 3,
			       1, 2, 2, 3, 2, 3, 3, 4 };
  int count = 0;
  while (x) {
    count += ctab[x & 0xfu];
    x >>= 4;
  }
  return (count);
}

/* --- @timer@ --- *
 *
 * Arguments:	@rand_pool *r@ = pointer to randomness pool
 *		@struct timeval *tv@ = pointer to time block
 *
 * Returns:	Nonzero if some randomness was contributed.
 *
 * Use:		Low-level timer contributor.
 */

static int timer(rand_pool *r, struct timeval *tv)
{
  unsigned long x, d, dd;
  int de, dde;
  int ret;

  x = tv->tv_usec + MILLION * tv->tv_sec;
  d = x ^ noise_last;
  dd = d ^ noise_diff;
  noise_last = x;
  noise_diff = d;
  de = bitcount(d);
  dde = bitcount(dd);
  rand_add(r, tv, sizeof(*tv), de <= dde ? de : dde);
  ret = (de || dde);
  BURN(tv); x = d = dd = de = dde = 0;
  return (ret);
}

/* --- @noise_timer@ --- *
 *
 * Arguments:	@rand_pool *r@ = pointer to a randomness pool
 *
 * Returns:	Nonzero if some randomness was contributed.
 *
 * Use:		Contributes the current time to the randomness pool.
 *		A guess at the number of useful bits contributed is made,
 *		based on first and second order bit differences.  This isn't
 *		ever-so	reliable, but it's better than nothing.
 */

int noise_timer(rand_pool *r)
{
  struct timeval tv;
  gettimeofday(&tv, 0);
  return (timer(r, &tv));
}

/* --- @noise_devrandom@ --- *
 *
 * Arguments:	@rand_pool *r@ = pointer to a randomness pool
 *
 * Returns:	Nonzero if some randomness was contributed.
 *
 * Use:		Attempts to obtain some randomness from the system entropy
 *		pool.  All bits from the device are assumed to be good.
 */

int noise_devrandom(rand_pool *r)
{
  int fd = -1;
  octet buf[RAND_POOLSZ];
  ssize_t len;
  size_t n = 0;
  int ret = 0;

  /* --- Be nice to other clients of the random device --- *
   *
   * Attempt to open the device nonblockingly.  If that works, take up to
   * one bufferful and then close again.  If there's no data to be read,
   * then that's tough and we go away again, on the grounds that the device
   * needs to get some more entropy from somewhere.
   */

  if (fd >= 0 ||
      (fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
      (fd = open("/dev/arandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
      (fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) {
    while (n < sizeof(buf)) {
      if ((len = read(fd, buf + n, sizeof(buf) - n)) <= 0) break;
      n += len;
    }
    if (n == sizeof(buf)) goto win;
  }
  goto done;

win:
  ret = 1;
done:
  if (fd >= 0) close(fd);
  rand_add(r, buf, n, 8*n);
  BURN(buf);
  noise_timer(r);
  return (ret);
}

/* --- @noise_setid@ --- *
 *
 * Arguments:	@uid_t uid@ = uid to set
 *		@gid_t gid@ = gid to set
 *
 * Returns:	---
 *
 * Use:		Sets the user and group ids to be used by @noise_filter@
 *		when running child processes.  This is useful to avoid
 *		giving shell commands (even carefully written ones) undue
 *		privileges.  This interface is Unix-specific
 */

void noise_setid(uid_t uid, gid_t gid)
{
  noise_uid = uid;
  noise_gid = gid;
}

/* --- @noise_filter@ --- *
 *
 * Arguments:	@rand_pool *r@ = pointer to a randomness pool
 *		@int good@ = number of good bits per 1024 bits
 *		@const char *c@ = shell command to run
 *
 * Returns:	Nonzero if some randomness was contributed.
 *
 * Use:		Attempts to execute a shell command, and dump it into the
 *		randomness pool.  A very rough estimate of the number of
 *		good bits is made, based on the size of the command's output.
 *		This function calls @waitpid@, so be careful.  Before execing
 *		the command, the process uid and gid are set to the values
 *		given to @noise_setid@, and an attempt is made to reset the
 *		list of supplementary groups.  The environment passed to
 *		the command has been severly lobotimized.  If the command
 *		fails to complete within a short time period, it is killed.
 *		Paranoid use of close-on-exec flags for file descriptors is
 *		recommended.
 *
 *		This interface is Unix-specific.
 */

struct noisekid {
  rand_pool *r;
  int good;
  char buf[4096];
  int donep;
  int ret;
};

static void kid_read(int fd, unsigned mode, void *p)
{
  struct noisekid *nk = p;
  ssize_t sz;
  int goodbits;

  noise_timer(nk->r);
  if ((sz = read(fd, nk->buf, sizeof(nk->buf))) <= 0)
    nk->donep = 1;
  else {
    goodbits = (sz * nk->good) / 128;
    rand_add(nk->r, nk->buf, sz, goodbits);
    nk->ret = 1;
  }
}

static void kid_dead(struct timeval *tv, void *p)
  { struct noisekid *nk = p; nk->donep = 1; }

int noise_filter(rand_pool *r, int good, const char *c)
{
  pid_t kid;
  int fd[2];
  struct timeval dead;
  int ret = 0;
  struct noisekid nk = { 0 };
  sel_state sel;
  sel_file sf;
  sel_timer st;
  const char *env[] = {
    "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc",
    0
  };

  /* --- Remember when this business started --- */

  gettimeofday(&dead, 0);
  timer(r, &dead);

  /* --- Create a pipe --- */

  if (pipe(fd))
    return (ret);

  /* --- Fork a child off --- */

  fflush(0);
  kid = fork();
  if (kid < 0) {
    close(fd[0]);
    close(fd[1]);
    return (ret);
  }

  /* --- Handle the child end of the deal --- */

  if (kid == 0) {
    mdup_fd mfd[3];
    int f, i = 0;

    /* --- Set the pipe as standard output, close standard input --- */

    if ((f = open("/dev/null", O_RDONLY)) < 0) _exit(127);
    mfd[i].cur = f; mfd[i].want = 0; i++;
    mfd[i].cur = fd[1]; mfd[i].want = 1; i++;
    mfd[i].cur = f; mfd[i].want = 2; i++;
    if (mdup(mfd, i)) _exit(127);

    /* --- Play games with uids --- */

    if (noise_gid != NOISE_NOSETGID) {
      setgid(noise_gid);
      setegid(noise_gid);
#ifdef HAVE_SETGROUPS
      setgroups(1, &noise_gid);
#endif
    }

    if (noise_uid != NOISE_NOSETUID) {
      setuid(noise_uid);
      seteuid(noise_uid);
    }

    /* --- Start the process up --- */

    execle("/bin/sh", "sh", "-c", c, (char *)0, env);
    _exit(127);
  }

  /* --- Sort out my end of the deal --- */

  close(fd[1]);
  sel_init(&sel);
  nk.r = r; nk.good = good;
  TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE);
  sel_initfile(&sel, &sf, fd[0], SEL_READ, kid_read, &nk);
  sel_addfile(&sf);
  sel_addtimer(&sel, &st, &dead, kid_dead, &nk);
  while (!nk.donep && !sel_select(&sel));

  /* --- We've finished with it: kill the child process --- *
   *
   * This is morally questionable.  On the other hand, I don't want to be
   * held up in the @waitpid@ call if I can possibly help it.  Maybe a
   * double-fork is worth doing here.
   */

  close(fd[0]);
  BURN(nk.buf);
  noise_timer(r);
  kill(kid, SIGKILL);
  waitpid(kid, 0, 0);
  return (nk.ret);
}

/* --- @noise_freewheel@ --- *
 *
 * Arguments:	@rand_pool *r@ = pointer to a randomness pool
 *
 * Returns:	Nonzero if some randomness was contributed.
 *
 * Use:		Runs a free counter for a short while as a desparate attempt
 *		to get randomness from somewhere.  This is actually quite
 *		effective.
 */

#ifdef USE_FREEWHEEL

static sigjmp_buf fwjmp;

static void fwalarm(int sig)
{
  siglongjmp(fwjmp, 1);
}

int noise_freewheel(rand_pool *r)
{
  void (*sigal)(int) = 0;
  struct itimerval oitv, itv = { { 0, 0 }, { 0, 5000 } };
  int rc = 0;
  volatile uint32 fwcount = 0;

  if (!sigsetjmp(fwjmp, 1)) {
    if ((sigal = signal(SIGALRM, fwalarm)) == SIG_ERR)
      return (0);
    if (setitimer(ITIMER_REAL, &itv, &oitv))
      goto done;
    for (;;)
      fwcount++;
  } else {
    octet buf[4];
    STORE32(buf, fwcount);
    rand_add(r, buf, sizeof(buf), 16);
    rc = 1;
  }

done:
  signal(SIGALRM, sigal);
  if (oitv.it_value.tv_sec || oitv.it_value.tv_usec)
    TV_SUB(&oitv.it_value, &oitv.it_value, &itv.it_value);
  setitimer(ITIMER_REAL, &oitv, 0);
  return (rc);
}

#else

int noise_freewheel(rand_pool *r)
{
  return (0);
}

#endif

/* --- @noise_enquire@ --- *
 *
 * Arguments:	@rand_pool *r@ = pointer to a randomness pool
 *
 * Returns:	Nonzero if some randomness was contributed.
 *
 * Use:		Runs some shell commands to enquire about the prevailing
 *		environment.  This can gather quite a lot of low-quality
 *		entropy.
 */

int noise_enquire(rand_pool *r)
{
  struct tab {
    const char *cmd;
    unsigned rate;
  } tab[] = {
    { "ps alxww || ps -elf",	16 },
    { "netstat -n",		 6 },
    { "ifconfig -a",		 8 },
    { "df",			20 },
    { "w",			 6 },
    { "ls -align /tmp/.",	10 },
    { 0,			 0 }
  };
  int i;

  for (i = 0; tab[i].cmd; i++)
    noise_filter(r, tab[i].rate, tab[i].cmd);
  return (1);
}

/* --- @noise_acquire@ --- *
 *
 * Arguments:	@rand_pool *r@ = pointer to a randomness pool
 *
 * Returns:	---
 *
 * Use:		Acquires some randomness from somewhere.
 */

void noise_acquire(rand_pool *r)
{
  unsigned i;
  for (i = 0; i < 8; i++)
    noise_freewheel(r);
  if (!noise_devrandom(r) || getenv("CATACOMB_FORCE_ESOTERIC_SOURCES")) {
    noise_enquire(r);
    for (i = 0; i < 8; i++)
      noise_freewheel(r);
  }
}

/*----- That's all, folks -------------------------------------------------*/