107 lines
3.0 KiB
Plaintext
107 lines
3.0 KiB
Plaintext
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#! /bin/sh
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### BEGIN INIT INFO
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# Provides: urandom
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# Required-Start: $local_fs $time
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# Required-Stop: $local_fs
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# Default-Start: S
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# Default-Stop: 0 6
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# Short-Description: Save and restore random seed between restarts.
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# Description: This script saves the random seed between restarts.
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# It is called from the boot, halt and reboot scripts.
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### END INIT INFO
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## Assumption 1: We assume $SAVEDFILE is a file (or a symlink
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## to a file) that resides on a non-volatile medium that persists
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## across reboots.
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## Case 1a: Ideally, it is readable and writeable. Its is unshared,
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## i.e. its contents are unique to this machine. It is protected so
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## that its contents are not known to attackers.
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## Case 1b: Less than ideally, it is read-only. Its contents are
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## unique to this machine and not known to attackers.
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SAVEDFILE=/var/lib/urandom/random-seed
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[ -c /dev/urandom ] || exit 0
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PATH=/sbin:/bin
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if ! POOLBYTES=$((
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($(cat /proc/sys/kernel/random/poolsize 2>/dev/null) + 7) / 8
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)) ; then
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POOLBYTES=512
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fi
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. /lib/init/vars.sh
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. /lib/lsb/init-functions
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do_status () {
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if [ -f $SAVEDFILE ] ; then
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return 0
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else
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return 4
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fi
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}
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case "$1" in
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start|"")
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[ "$VERBOSE" = no ] || log_action_begin_msg "Initializing random number generator"
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# Seed the RNG with date and time.
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# This is helpful in the less-than-ideal case where $SAVEDFILE
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# is read-only.
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# The value of this is greatly reduced if $SAVEDFILE is missing,
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# or its contents are shared machine-to-machine or known to
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# attackers (since they might well know at what time this
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# machine booted up).
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(
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date +%s.%N
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# Load and then save $POOLBYTES bytes,
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# which is the size of the entropy pool
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if [ -f "$SAVEDFILE" ]
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then
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cat "$SAVEDFILE"
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fi
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# Redirect output of subshell (not individual commands)
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# to cope with a misfeature in the FreeBSD (not Linux)
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# /dev/random, where every superuser write/close causes
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# an explicit reseed of the yarrow.
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) >/dev/urandom
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# Write a new seed into $SAVEDFILE because re-using a seed
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# compromises security. Each time we re-seed, we want the
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# seed to be as different as possible.
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# Write it now, in case the machine crashes without doing
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# an orderly shutdown.
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# The write will fail if $SAVEDFILE is read-only, but it
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# doesn't hurt to try.
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umask 077
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dd if=/dev/urandom of=$SAVEDFILE bs=$POOLBYTES count=1 >/dev/null 2>&1
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ES=$?
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umask 022
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[ "$VERBOSE" = no ] || log_action_end_msg $ES
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;;
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stop)
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# Carry a random seed from shut-down to start-up;
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# Write it on shutdown, in case the one written at startup
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# has been lost, snooped, or otherwise compromised.
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# see documentation in linux/drivers/char/random.c
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[ "$VERBOSE" = no ] || log_action_begin_msg "Saving random seed"
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umask 077
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dd if=/dev/urandom of=$SAVEDFILE bs=$POOLBYTES count=1 >/dev/null 2>&1
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ES=$?
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[ "$VERBOSE" = no ] || log_action_end_msg $ES
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;;
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status)
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do_status
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exit $?
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;;
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restart|reload|force-reload)
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echo "Error: argument '$1' not supported" >&2
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exit 3
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;;
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*)
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echo "Usage: urandom start|stop" >&2
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exit 3
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;;
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esac
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:
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