freebsd-dev/libexec/save-entropy/save-entropy.sh
Xin LI 46413cedf7 Reduce disk write load in /usr/libexec/save-entropy.
Before this commit, the save-entropy script rotates entropy files
like logs. This involves creating a new file that holds the entropy
and renaming of all existing entropy files. However, the entropy
data do not really need to be kept in a particular order, and
replacing the oldest file is sufficient.

This commit replaces the rotation with a scan in the
[1..entropy_save_num] space that finds the first empty slot, or
the slot of the oldest file, and writes entropy into that slot.

This also fixes an issue that prevents save-entropy from saving
any entropy when there is one non-regular file in any slot as a
side effect.

Based on an earlier patch from peterj@.

PR:		134225
Reported by:	peterj
Reviewed by:	csprng (cem, markm)
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D22612
2019-11-30 20:06:53 +00:00

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#!/bin/sh
#
# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
#
# Copyright (c) 2001-2006,2012 Douglas Barton, dougb@FreeBSD.org
# 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.
#
# $FreeBSD$
# 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, dougb@FreeBSD.org
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