Hi Etienne,
Hi Arjen,
Hi John,
Hi Jo,
while wondering which process is blocking my rootfs from being
unmounted for sysupgrade I discovered that getrandom story going
on and while waiting for blocking I/O read from /dev/urandom, it
even ignored any TERM or KILL signals.
This then prevented the rootfs from unmounting and thus the ubi
device from detaching. The sysupgrade script, however, seems not to
care about that and just started ubiformat anyway and managed to
format and flash most of the NAND -- and by doing to, filling up the
random pool, which then resulted in /etc/urandom.seed being created
and ruining what was just written. If it wasn't for the serial
console being already hooked up, the device would have been bricked.
Please be more careful when making such fundamental changes such
as this one. Btw, it also prevents reboot until random seed is
written.
Please fix getrandom to be more graceful and use non-blocking reads
with (delayed) retries or something like that.
Cheers
Daniel
On Tue, Jun 28, 2016 at 12:55:57PM +0200, Etienne Champetier wrote:
> Hi Arjen,
>
> 2016-06-28 11:52 GMT+02:00 Arjen de Korte <arjen+l...@de-korte.org>:
> > Citeren John Crispin <j...@phrozen.org>:
> >
> >> On 28/06/2016 10:28, Jo-Philipp Wich wrote:
> >>>
> >>> Hi Etienne,
> >>>
> >>> I like this approach, fine with me now.
> >>>
> >>
> >> same here, we could not also consider adding a uci-defaults script that
> >> check if rootfs is on a mtd or real lbock device and change the default
> >> during firstboot, but i guess that would be a new patch. i have just
> >> pulled this into my staging tree
> >
> >
> > Would it be useful to list /etc/urandom.seed in
> > package/base-files/files/lib/upgrade/keep.d/base-files-essential to keep on
> > sysupgrade? Or would this break if the file does not exist? In that case, it
> > might be useful to make a note to add it to /etc/sysupgrade.conf if the
> > contents should be kept on upgrades.
> >
>
> We can keep /etc/urandom.seed on upgrade, be we shouldn't include it
> in config backup
>
> >
> >>> On 06/27/2016 05:53 PM, Etienne CHAMPETIER wrote:
> >>>>
> >>>> This commit:
> >>>> 1) seed /dev/urandom with the saved seeds as early as possible
> >>>> (see /lib/preinit/81_urandom_seed)
> >>>> 2) save a seed at /etc/urandom.seed if it doesn't exists
> >>>> 3) save a new seed each boot at "system.@system[0].urandom_seed"
> >>>> (see /etc/init.d/urandom_seed)
> >>>>
> >>>> We use getrandom() so we are sure /dev/urandom pool is initialized
> >>>>
> >>>> 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
> >>>>
> >>>> 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
> >>>>
> >>>> Saving a new seed on each boot is disabled by default to avoid too much
> >>>> writes without user consent
> >>>>
> >>>> 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 uci config param
> >>>> v5: config param is now the path of the seed
> >>>>
> >>>> Signed-off-by: Etienne CHAMPETIER <champetier.etie...@gmail.com>
> >>>
> >>> Acked-by: Jo-Philipp Wich <j...@mein.io>
> >>>>
> >>>> ---
> >>>> package/base-files/files/bin/config_generate | 1 +
> >>>> package/base-files/files/etc/init.d/urandom_seed | 29
> >>>> ++++++++++++++++++++++
> >>>> .../base-files/files/lib/preinit/81_urandom_seed | 24
> >>>> ++++++++++++++++++
> >>>> 3 files changed, 54 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..c0ba0fb 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].urandom_seed='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..cb2eb44
> >>>> --- /dev/null
> >>>> +++ b/package/base-files/files/etc/init.d/urandom_seed
> >>>> @@ -0,0 +1,29 @@
> >>>> +#!/bin/sh /etc/rc.common
> >>>> +
> >>>> +START=99
> >>>> +
> >>>> +EXTRA_COMMANDS="save"
> >>>> +
> >>>> +_log() {
> >>>> + logger -t urandom_seed "$1"
> >>>> +}
> >>>> +
> >>>> +_save() {
> >>>> + touch $1.tmp || { _log "touch $1 failed"; return; }
> >>>> + chown root:root $1.tmp || { _log "chown $1 failed"; return; }
> >>>> + chmod 600 $1.tmp || { _log "chmod $1 failed"; return; }
> >>>> + getrandom 512 > $1.tmp || { _log "getrandom failed"; return; }
> >>>> + mv $1.tmp $1 || { _log "mv $1 failed"; return; }
> >>>> +}
> >>>> +
> >>>> +save() {
> >>>> + SEED="$(uci -q get system.@system[0].urandom_seed)"
> >>>> + [ "${SEED:0:1}" == "/" ] && _save "$SEED" && _log "Seed saved
> >>>> ($SEED)"
> >>>> +
> >>>> + SEED=/etc/urandom.seed
> >>>> + [ ! -f $SEED ] && _save "$SEED" && _log "Seed saved ($SEED)"
> >>>> +}
> >>>> +
> >>>> +boot() {
> >>>> + 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..10878f3
> >>>> --- /dev/null
> >>>> +++ b/package/base-files/files/lib/preinit/81_urandom_seed
> >>>> @@ -0,0 +1,24 @@
> >>>> +#!/bin/sh
> >>>> +
> >>>> +log_urandom_seed() {
> >>>> + echo "urandom-seed: $1" > /dev/kmsg
> >>>> +}
> >>>> +
> >>>> +_do_urandom_seed() {
> >>>> + [ -f "$1" ] || { log_urandom_seed "Seed file not found ($1)";
> >>>> return; }
> >>>> + [ -O "$1" -a -G "$1" -a ! -x "$1" ] || { log_urandom_seed "Wrong
> >>>> owner / permissions for $1"; return; }
> >>>> +
> >>>> + log_urandom_seed "Seeding with $1"
> >>>> + cat "$1" > /dev/urandom
> >>>> +}
> >>>> +
> >>>> +do_urandom_seed() {
> >>>> + [ -c /dev/urandom ] || { log_urandom_seed "Something is wrong with
> >>>> /dev/urandom"; return; }
> >>>> +
> >>>> + _do_urandom_seed "/etc/urandom.seed"
> >>>> +
> >>>> + SEED="$(uci -q get system.@system[0].urandom_seed)"
> >>>> + [ "${SEED:0:1}" == "/" -a "$SEED" != "/etc/urandom.seed" ] &&
> >>>> _do_urandom_seed "$SEED"
> >>>> +}
> >>>> +
> >>>> +boot_hook_add preinit_main do_urandom_seed
> >>>>
> >>>
> >>>
>
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