source: trunk/third/openssh/entropy.c @ 18759

/*
 * Copyright (c) 2001 Damien Miller.  All rights reserved.
 *
 * 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, this list of conditions and the following disclaimer.
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 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 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <openssl/rand.h>
#include <openssl/crypto.h>

#include "ssh.h"
#include "misc.h"
#include "xmalloc.h"
#include "atomicio.h"
#include "pathnames.h"
#include "log.h"

/*
 * Portable OpenSSH PRNG seeding:
 * If OpenSSL has not "internally seeded" itself (e.g. pulled data from 
 * /dev/random), then we execute a "ssh-rand-helper" program which 
 * collects entropy and writes it to stdout. The child program must 
 * write at least RANDOM_SEED_SIZE bytes. The child is run with stderr
 * attached, so error/debugging output should be visible.
 *
 * XXX: we should tell the child how many bytes we need.
 */

RCSID("$Id: entropy.c,v 1.1.1.2 2003-02-05 19:02:58 zacheiss Exp $");

#ifndef OPENSSL_PRNG_ONLY
#define RANDOM_SEED_SIZE 48
static uid_t original_uid, original_euid;
#endif

void
seed_rng(void)
{
#ifndef OPENSSL_PRNG_ONLY
        int devnull;
        int p[2];
        pid_t pid;
        int ret;
        unsigned char buf[RANDOM_SEED_SIZE];
        mysig_t old_sigchld;

        if (RAND_status() == 1) {
                debug3("RNG is ready, skipping seeding");
                return;
        }

        debug3("Seeding PRNG from %s", SSH_RAND_HELPER);

        if ((devnull = open("/dev/null", O_RDWR)) == -1)
                fatal("Couldn't open /dev/null: %s", strerror(errno));
        if (pipe(p) == -1)
                fatal("pipe: %s", strerror(errno));

        old_sigchld = mysignal(SIGCHLD, SIG_DFL);
        if ((pid = fork()) == -1)
                fatal("Couldn't fork: %s", strerror(errno));
        if (pid == 0) {
                dup2(devnull, STDIN_FILENO);
                dup2(p[1], STDOUT_FILENO);
                /* Keep stderr open for errors */
                close(p[0]);
                close(p[1]);
                close(devnull);

                if (original_uid != original_euid && 
                    ( seteuid(getuid()) == -1 || 
                      setuid(original_uid) == -1) ) {
                        fprintf(stderr, "(rand child) setuid(%d): %s\n", 
                            original_uid, strerror(errno));
                        _exit(1);
                }
                
                execl(SSH_RAND_HELPER, "ssh-rand-helper", NULL);
                fprintf(stderr, "(rand child) Couldn't exec '%s': %s\n", 
                    SSH_RAND_HELPER, strerror(errno));
                _exit(1);
        }

        close(devnull);
        close(p[1]);

        memset(buf, '\0', sizeof(buf));
        ret = atomicio(read, p[0], buf, sizeof(buf));
        if (ret == -1)
                fatal("Couldn't read from ssh-rand-helper: %s",
                    strerror(errno));
        if (ret != sizeof(buf))
                fatal("ssh-rand-helper child produced insufficient data");

        close(p[0]);

        if (waitpid(pid, &ret, 0) == -1)
               fatal("Couldn't wait for ssh-rand-helper completion: %s", 
                   strerror(errno));
        mysignal(SIGCHLD, old_sigchld);

        /* We don't mind if the child exits upon a SIGPIPE */
        if (!WIFEXITED(ret) && 
            (!WIFSIGNALED(ret) || WTERMSIG(ret) != SIGPIPE))
                fatal("ssh-rand-helper terminated abnormally");
        if (WEXITSTATUS(ret) != 0)
                fatal("ssh-rand-helper exit with exit status %d", ret);

        RAND_add(buf, sizeof(buf), sizeof(buf));
        memset(buf, '\0', sizeof(buf));

#endif /* OPENSSL_PRNG_ONLY */
        if (RAND_status() != 1)
                fatal("PRNG is not seeded");
}

void
init_rng(void) 
{
        /*
         * OpenSSL version numbers: MNNFFPPS: major minor fix patch status
         * We match major, minor, fix and status (not patch)
         */
        if ((SSLeay() ^ OPENSSL_VERSION_NUMBER) & ~0xff0L)
                fatal("OpenSSL version mismatch. Built against %lx, you "
                    "have %lx", OPENSSL_VERSION_NUMBER, SSLeay());

#ifndef OPENSSL_PRNG_ONLY
        if ((original_uid = getuid()) == -1)
                fatal("getuid: %s", strerror(errno));
        if ((original_euid = geteuid()) == -1)
                fatal("geteuid: %s", strerror(errno));
#endif
}