save-entropy.sh

#!/bin/sh
#
# SPDX-License-Identifier: BSD-2-Clause
#
# Copyright (c) 2001-2006,2012 Douglas Barton, [email protected]
# 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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.
#

# This script is called by cron to store bits of randomness which are
# then used to seed /dev/random on boot.

# Originally developed by Doug Barton, [email protected]

PATH=/bin:/usr/bin

# If there is a global system configuration file, suck it in.
#
if [ -r /etc/defaults/rc.conf ]; then
	. /etc/defaults/rc.conf
	source_rc_confs 2>/dev/null
elif [ -r /etc/rc.conf ]; then
	. /etc/rc.conf 2>/dev/null
fi

[ $(/sbin/sysctl -n security.jail.jailed) = 0 ] || exit 0

case ${entropy_dir} in
[Nn][Oo])
	exit 0
	;;
*)
	entropy_dir=${entropy_dir:-/var/db/entropy}
	;;
esac

entropy_save_sz=${entropy_save_sz:-4096}
entropy_save_num=${entropy_save_num:-8}

if [ ! -d "${entropy_dir}" ]; then
	install -d -o operator -g operator -m 0700 "${entropy_dir}" || {
		logger -is -t "$0" The entropy directory "${entropy_dir}" does \
		    not exist, and cannot be created. Therefore no entropy can \
		    be saved.; exit 1; }
fi

cd "${entropy_dir}" || {
	logger -is -t "$0" Cannot cd to the entropy directory: "${entropy_dir}". \
	    Entropy file rotation is aborted.; exit 1; }

for f in saved-entropy.*; do
	case "${f}" in saved-entropy.\*) continue ;; esac	# No files match
	[ ${f#saved-entropy\.} -gt ${entropy_save_num} ] && unlink ${f}
done

umask 177

# Scan slots [1..$entropy_save_num), picking an empty slot or the oldest
# existing file if no empty slot was available.
#
# 1. Find out the first regular file or empty slot (and its serial number)
#
n=1
while [ ${n} -le ${entropy_save_num} ]; do
	save_file="saved-entropy.${n}"
	if [ ! -e "${save_file}" -o -f "${save_file}" ]; then
		break
	else
		logger -is -t "$0" \
		    "${save_file}" is not a regular file, skipped.
	fi
	n=$(( ${n} + 1 ))
done
#
# 2. Start from (serial number + 1), and check if the slot is empty
#    or is an older regular file, update save_file pointer in either
#    case, and break early if we found an empty slot.
#
if [ -f ${save_file} ]; then
	n=$(( ${n} + 1 ))
	while [ ${n} -le ${entropy_save_num} ]; do
		next_file=saved-entropy.${n}
		if [ -f "${next_file}" ]; then
			[ "${next_file}" -ot "${save_file}" ] && \
			    save_file="${next_file}"
		elif [ ! -e "${next_file}" ]; then
			save_file="${next_file}"
			break
		else
			logger -is -t "$0" \
			    "${next_file}" is not a regular file, skipped.
		fi
		n=$(( ${n} + 1 ))
	done
fi
#
# 3. Check if the pointer we have in hand is really a regular file or
#    an empty slot, and bail out as that means there is no available slot.
#
if [ -e "${save_file}" -a ! -f "${save_file}" ]; then
	logger -is -t "$0" \
		No available slot in "${entropy_dir}", save entropy is aborted.
	exit 1
fi

# Save entropy to the selected slot.
chmod 600 "${save_file}" 2>/dev/null || :
dd if=/dev/random of="${save_file}" bs=${entropy_save_sz} count=1 2>/dev/null
chflags nodump "${save_file}" 2>/dev/null || :
fsync "${save_file}" "."

exit 0