ssh-rand-helper.c

OpenSSL Source code for SFTP, SSH, and many others

	long int i;

	total_entropy_estimate = 0;

	i = getpid();
	RAND_add(&i, sizeof(i), 0.5);
	total_entropy_estimate += 0.1;

	i = getppid();
	RAND_add(&i, sizeof(i), 0.5);
	total_entropy_estimate += 0.1;

	i = getuid();
	RAND_add(&i, sizeof(i), 0.0);
	i = getgid();
	RAND_add(&i, sizeof(i), 0.0);

	total_entropy_estimate += stir_gettimeofday(1.0);
	total_entropy_estimate += stir_clock(0.5);
	total_entropy_estimate += stir_rusage(RUSAGE_SELF, 2.0);

	return total_entropy_estimate;
}

double
stir_from_programs(void)
{
	int c;
	double entropy, total_entropy;
	char hash[SHA_DIGEST_LENGTH];

	total_entropy = 0;
	for(c = 0; entropy_cmds[c].path != NULL; c++) {
		if (!entropy_cmds[c].badness) {
			/* Hash output from command */
			entropy = hash_command_output(&entropy_cmds[c],
			    hash);

			/* Scale back estimate by command's rate */
			entropy *= entropy_cmds[c].rate;

			/* Upper bound of entropy is SHA_DIGEST_LENGTH */
			if (entropy > SHA_DIGEST_LENGTH)
				entropy = SHA_DIGEST_LENGTH;

			/* Stir it in */
			RAND_add(hash, sizeof(hash), entropy);

			debug3("Got %0.2f bytes of entropy from '%s'", 
			    entropy, entropy_cmds[c].cmdstring);

			total_entropy += entropy;

			/* Execution time should be a bit unpredictable */
			total_entropy += stir_gettimeofday(0.05);
			total_entropy += stir_clock(0.05);
			total_entropy += stir_rusage(RUSAGE_SELF, 0.1);
			total_entropy += stir_rusage(RUSAGE_CHILDREN, 0.1);
		} else {
			debug2("Command '%s' disabled (badness %d)",
			    entropy_cmds[c].cmdstring, 
			    entropy_cmds[c].badness);

			if (entropy_cmds[c].badness > 0)
				entropy_cmds[c].badness--;
		}
	}

	return total_entropy;
}

/*
 * prng seedfile functions
 */
int
prng_check_seedfile(char *filename)
{
	struct stat st;

	/*
	 * XXX raceable: eg replace seed between this stat and subsequent 
	 * open. Not such a problem because we don't really trust the 
	 * seed file anyway.
	 * XXX: use secure path checking as elsewhere in OpenSSH
	 */
	if (lstat(filename, &st) == -1) {
		/* Give up on hard errors */
		if (errno != ENOENT)
			debug("WARNING: Couldn't stat random seed file "
			    "\"%.100s\": %s", filename, strerror(errno));
		return 0;
	}

	/* regular file? */
	if (!S_ISREG(st.st_mode))
		fatal("PRNG seedfile %.100s is not a regular file",
		    filename);

	/* mode 0600, owned by root or the current user? */
	if (((st.st_mode & 0177) != 0) || !(st.st_uid == getuid())) {
		debug("WARNING: PRNG seedfile %.100s must be mode 0600, "
		    "owned by uid %d", filename, getuid());
		return 0;
	}

	return 1;
}

void
prng_write_seedfile(void)
{
	int fd;
	char seed[SEED_FILE_SIZE], filename[MAXPATHLEN];
	struct passwd *pw;

	pw = getpwuid(getuid());
	if (pw == NULL)
		fatal("Couldn't get password entry for current user "
		    "(%i): %s", getuid(), strerror(errno));

	/* Try to ensure that the parent directory is there */
	snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
	    _PATH_SSH_USER_DIR);
	mkdir(filename, 0700);

	snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
	    SSH_PRNG_SEED_FILE);

	debug("writing PRNG seed to file %.100s", filename);

	RAND_bytes(seed, sizeof(seed));

	/* Don't care if the seed doesn't exist */
	prng_check_seedfile(filename);

	if ((fd = open(filename, O_WRONLY|O_TRUNC|O_CREAT, 0600)) == -1) {
		debug("WARNING: couldn't access PRNG seedfile %.100s "
		    "(%.100s)", filename, strerror(errno));
	} else {
		if (atomicio(write, fd, &seed, sizeof(seed)) < sizeof(seed))
			fatal("problem writing PRNG seedfile %.100s "
			    "(%.100s)", filename, strerror(errno));
		close(fd);
	}
}

void
prng_read_seedfile(void)
{
	int fd;
	char seed[SEED_FILE_SIZE], filename[MAXPATHLEN];
	struct passwd *pw;

	pw = getpwuid(getuid());
	if (pw == NULL)
		fatal("Couldn't get password entry for current user "
		    "(%i): %s", getuid(), strerror(errno));

	snprintf(filename, sizeof(filename), "%.512s/%s", pw->pw_dir,
		SSH_PRNG_SEED_FILE);

	debug("loading PRNG seed from file %.100s", filename);

	if (!prng_check_seedfile(filename)) {
		verbose("Random seed file not found or invalid, ignoring.");
		return;
	}

	/* open the file and read in the seed */
	fd = open(filename, O_RDONLY);
	if (fd == -1)
		fatal("could not open PRNG seedfile %.100s (%.100s)",
		    filename, strerror(errno));

	if (atomicio(read, fd, &seed, sizeof(seed)) < sizeof(seed)) {
		verbose("invalid or short read from PRNG seedfile "
		    "%.100s - ignoring", filename);
		memset(seed, '\0', sizeof(seed));
	}
	close(fd);

	/* stir in the seed, with estimated entropy zero */
	RAND_add(&seed, sizeof(seed), 0.0);
}


/*
 * entropy command initialisation functions
 */
int
prng_read_commands(char *cmdfilename)
{
	char cmd[SEED_FILE_SIZE], *cp, line[1024], path[SEED_FILE_SIZE];
	double est;
	entropy_cmd_t *entcmd;
	FILE *f;
	int cur_cmd, linenum, num_cmds, arg;

	if ((f = fopen(cmdfilename, "r")) == NULL) {
		fatal("couldn't read entropy commands file %.100s: %.100s",
		    cmdfilename, strerror(errno));
	}

	num_cmds = 64;
	entcmd = xmalloc(num_cmds * sizeof(entropy_cmd_t));
	memset(entcmd, '\0', num_cmds * sizeof(entropy_cmd_t));

	/* Read in file */
	cur_cmd = linenum = 0;
	while (fgets(line, sizeof(line), f)) {
		linenum++;

		/* Skip leading whitespace, blank lines and comments */
		cp = line + strspn(line, WHITESPACE);
		if ((*cp == 0) || (*cp == '#'))
			continue; /* done with this line */

		/*
		 * The first non-whitespace char should be a double quote 
		 * delimiting the commandline
		 */
		if (*cp != '"') {
			error("bad entropy command, %.100s line %d",
			    cmdfilename, linenum);
			continue;
		}

		/*
		 * First token, command args (incl. argv[0]) in double
		 * quotes
		 */
		cp = strtok(cp, "\"");
		if (cp == NULL) {
			error("missing or bad command string, %.100s "
			    "line %d -- ignored", cmdfilename, linenum);
			continue;
		}
		strlcpy(cmd, cp, sizeof(cmd));

		/* Second token, full command path */
		if ((cp = strtok(NULL, WHITESPACE)) == NULL) {
			error("missing command path, %.100s "
			    "line %d -- ignored", cmdfilename, linenum);
			continue;
		}

		/* Did configure mark this as dead? */
		if (strncmp("undef", cp, 5) == 0)
			continue;

		strlcpy(path, cp, sizeof(path));

		/* Third token, entropy rate estimate for this command */
		if ((cp = strtok(NULL, WHITESPACE)) == NULL) {
			error("missing entropy estimate, %.100s "
			    "line %d -- ignored", cmdfilename, linenum);
			continue;
		}
		est = strtod(cp, NULL);

		/* end of line */
		if ((cp = strtok(NULL, WHITESPACE)) != NULL) {
			error("garbage at end of line %d in %.100s "
			    "-- ignored", linenum, cmdfilename);
			continue;
		}

		/* save the command for debug messages */
		entcmd[cur_cmd].cmdstring = xstrdup(cmd);

		/* split the command args */
		cp = strtok(cmd, WHITESPACE);
		arg = 0;
		do {
			entcmd[cur_cmd].args[arg] = xstrdup(cp);
			arg++;
		} while(arg < NUM_ARGS && (cp = strtok(NULL, WHITESPACE)));

		if (strtok(NULL, WHITESPACE))
			error("ignored extra commands (max %d), %.100s "
			    "line %d", NUM_ARGS, cmdfilename, linenum);

		/* Copy the command path and rate estimate */
		entcmd[cur_cmd].path = xstrdup(path);
		entcmd[cur_cmd].rate = est;

		/* Initialise other values */
		entcmd[cur_cmd].sticky_badness = 1;

		cur_cmd++;

		/*
		 * If we've filled the array, reallocate it twice the size
		 * Do this now because even if this we're on the last 
		 * command we need another slot to mark the last entry
		 */
		if (cur_cmd == num_cmds) {
			num_cmds *= 2;
			entcmd = xrealloc(entcmd, num_cmds *
			    sizeof(entropy_cmd_t));
		}
	}

	/* zero the last entry */
	memset(&entcmd[cur_cmd], '\0', sizeof(entropy_cmd_t));

	/* trim to size */
	entropy_cmds = xrealloc(entcmd, (cur_cmd + 1) *
	    sizeof(entropy_cmd_t));

	debug("Loaded %d entropy commands from %.100s", cur_cmd,
	    cmdfilename);

	return cur_cmd < MIN_ENTROPY_SOURCES ? -1 : 0;
}

void
usage(void)
{
	fprintf(stderr, "Usage: %s [options]\n", __progname);
	fprintf(stderr, "  -v          Verbose; display verbose debugging messages.\n");
	fprintf(stderr, "              Multiple -v increases verbosity.\n");
	fprintf(stderr, "  -x          Force output in hexidecimal (for debugging)\n");
	fprintf(stderr, "  -X          Force output in binary\n");
	fprintf(stderr, "  -b bytes    Number of bytes to output (default %d)\n",
	    OUTPUT_SEED_SIZE);
}

int 
main(int argc, char **argv)
{
	unsigned char *buf;
	int ret, ch, debug_level, output_hex, bytes;
	extern char *optarg;
	LogLevel ll;

	__progname = get_progname(argv[0]);
	log_init(argv[0], SYSLOG_LEVEL_INFO, SYSLOG_FACILITY_USER, 1);

	ll = SYSLOG_LEVEL_INFO;
	debug_level = output_hex = 0;
	bytes = OUTPUT_SEED_SIZE;

	/* Don't write binary data to a tty, unless we are forced to */
	if (isatty(STDOUT_FILENO))
		output_hex = 1;
	
	while ((ch = getopt(argc, argv, "vxXhb:")) != -1) {
		switch (ch) {
		case 'v':
			if (debug_level < 3)
				ll = SYSLOG_LEVEL_DEBUG1 + debug_level++;
			break;
		case 'x':
			output_hex = 1;
			break;
		case 'X':
			output_hex = 0;
			break;
		case 'b':
			if ((bytes = atoi(optarg)) <= 0)
				fatal("Invalid number of output bytes");
			break;
		case 'h':
			usage();
			exit(0);
		default:
			error("Invalid commandline option");
			usage();
		}
	}

	log_init(argv[0], ll, SYSLOG_FACILITY_USER, 1);
	
#ifdef USE_SEED_FILES
	prng_read_seedfile();
#endif

	buf = xmalloc(bytes);

	/*
	 * Seed the RNG from wherever we can
	 */
	 
	/* Take whatever is on the stack, but don't credit it */
	RAND_add(buf, bytes, 0);

	debug("Seeded RNG with %i bytes from system calls", 
	    (int)stir_from_system());

#ifdef PRNGD_PORT
	if (get_random_bytes_prngd(buf, bytes, PRNGD_PORT, NULL) == -1)
		fatal("Entropy collection failed");
	RAND_add(buf, bytes, bytes);
#elif defined(PRNGD_SOCKET)
	if (get_random_bytes_prngd(buf, bytes, 0, PRNGD_SOCKET) == -1)
		fatal("Entropy collection failed");
	RAND_add(buf, bytes, bytes);
#else
	/* Read in collection commands */
	if (prng_read_commands(SSH_PRNG_COMMAND_FILE) == -1)
		fatal("PRNG initialisation failed -- exiting.");
	debug("Seeded RNG with %i bytes from programs", 
	    (int)stir_from_programs());
#endif

#ifdef USE_SEED_FILES
	prng_write_seedfile();
#endif

	/*
	 * Write the seed to stdout
	 */

	if (!RAND_status())
		fatal("Not enough entropy in RNG");

	RAND_bytes(buf, bytes);

	if (output_hex) {
		for(ret = 0; ret < bytes; ret++)
			printf("%02x", (unsigned char)(buf[ret]));
		printf("\n");
	} else
		ret = atomicio(write, STDOUT_FILENO, buf, bytes);
		
	memset(buf, '\0', bytes);
	xfree(buf);
	
	return ret == bytes ? 0 : 1;
}