This commit:
1) seed /dev/urandom with a saved seed as early as possible
(see /lib/preinit/81_urandom_seed)
2) save a new seed if system.@system[0].write_urandom_seed_on_boot == 1
or if none exists. We use getrandom() so we are sure /dev/urandom
pool is initialized (see /etc/init.d/urandom_seed)
seed size is 512 bytes (ie /proc/sys/kernel/random/poolsize / 8)
it's the same size as in ubuntu 14.04 and all systemd systems
seed file is /etc/urandom.seed (need a writable path)
seeding /dev/urandom doesn't change entropy estimation, so we still have
"random: ubus urandom read with 4 bits of entropy available"
messages in the logs, but we can now ignore them if
after "urandom-seed: Seeding with ..." message
for now saving a new seed is disabled by default as Felix and John
are concerned we might write too much and destroy the flash
v2: log preinit messages to /dev/kmsg
v3: use non generic function name for logging, as /lib/preinit/ files
are all sourced together in /etc/preinit
v4: after a lot of discussion on the ML, use a config param
Signed-off-by: Etienne CHAMPETIER <champetier.etie...@gmail.com>
---
package/base-files/files/bin/config_generate | 1 +
package/base-files/files/etc/init.d/urandom_seed | 28 ++++++++++++++++++++++
.../base-files/files/lib/preinit/81_urandom_seed | 19 +++++++++++++++
3 files changed, 48 insertions(+)
create mode 100755 package/base-files/files/etc/init.d/urandom_seed
create mode 100644 package/base-files/files/lib/preinit/81_urandom_seed
diff --git a/package/base-files/files/bin/config_generate
b/package/base-files/files/bin/config_generate
index 8002bc4..9bccead 100755
--- a/package/base-files/files/bin/config_generate
+++ b/package/base-files/files/bin/config_generate
@@ -230,6 +230,7 @@ generate_static_system() {
set system.@system[-1].timezone='UTC'
set system.@system[-1].ttylogin='0'
set system.@system[-1].log_size='64'
+ set system.@system[-1].write_urandom_seed_on_boot='0'
delete system.ntp
set system.ntp='timeserver'
diff --git a/package/base-files/files/etc/init.d/urandom_seed
b/package/base-files/files/etc/init.d/urandom_seed
new file mode 100755
index 0000000..f950685
--- /dev/null
+++ b/package/base-files/files/etc/init.d/urandom_seed
@@ -0,0 +1,28 @@
+#!/bin/sh /etc/rc.common
+
+START=99
+
+EXTRA_COMMANDS="save"
+
+SEED=/etc/urandom.seed
+
+error_exit() {
+ logger -t urandom_seed "$1"
+ exit 1
+}
+
+save() {
+ touch $SEED.tmp || error_exit "touch failed"
+ chown root:root $SEED.tmp || error_exit "chown failed"
+ chmod 600 $SEED.tmp || error_exit "chmod failed"
+ getrandom 512 > $SEED.tmp || error_exit "getrandom failed"
+ mv $SEED.tmp $SEED || error_exit "mv failed"
+}
+
+boot() {
+ [ -f $SEED ] || {
+ save
+ exit 0
+ }
+ [ "$(uci get system.@system[0].write_urandom_seed_on_boot)" == "1" ] &&
save
+}
diff --git a/package/base-files/files/lib/preinit/81_urandom_seed
b/package/base-files/files/lib/preinit/81_urandom_seed
new file mode 100644
index 0000000..a1457aa
--- /dev/null
+++ b/package/base-files/files/lib/preinit/81_urandom_seed
@@ -0,0 +1,19 @@
+#!/bin/sh
+
+log_urandom_seed() {
+ echo "urandom-seed: $1" > /dev/kmsg
+}
+
+do_urandom_seed() {
+ S=/etc/urandom.seed
+ U=/dev/urandom
+
+ [ -c $U ] || { log_urandom_seed "Something is wrong with $U"; return; }
+ [ -f $S ] || { log_urandom_seed "Seed file not found ($S)"; return; }
+ [ -O $S -a -G $S -a ! -x $S ] || { log_urandom_seed "Wrong owner /
permissions for $S"; return; }
+
+ log_urandom_seed "Seeding with $S"
+ cat $S > $U
+}
+
+boot_hook_add preinit_main do_urandom_seed
--
1.9.1
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