linux-kernel - System reboot triggered by just reading a device file....!?

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Date:	Wed, 21 Nov 2007 00:06:57 +0100
From:	devzero@....de
To:	linux-kernel@...r.kernel.org
Subject: System reboot triggered by just reading a device file....!?

good evening, 

i stumbled over some funny issue when trying windirstat (like KDirStat) with wine.

after running that tool for a while my system rebooted. i could reproduce this with every run.

after some deep investigation (i thought i had stability issues with my system and spent more than an hour on this) i found out, that the reboot is being triggered by iTCO_wdt ( /dev/watchdog )

this is how to reproduce:

- be root
-  cat /dev/watchdog or dd if=/dev/watchdog of=/dev/zero bs=1 count=1 or .....
-  wait one minute........

*reboot*!

i have heard 2 opinions for now (contacted the author and also discussed on wine-devel ) that this should be expected behaviour.

being sysadmin quite a while, i cannot believe that (accidentally) reading a device file (being root or not - what does that matter) triggers a system reboot.

ok - when i`m root , i shouldn`t do stupid things and be careful, but i thought reading/crawling trough a filesystem (r/o, btw.) with some tool which is built to do exactly this wasn`t so stupid - even from within wine.

think of an admin writing a quick&dirty script for intrusion detection (find / -exec md5sum {} \; >/tmp/need-no-tripwire) and forgetting to exclude /dev, /sys or /proc appropriately......
think of someone exporting "/" via samba (readonly) and then navigating trough the /dev directory....

stupid?
i don`t think so.....i have seen worse things...... :)

should someone get punished  by an accidental system reboot and should he need to spend his time on this to investigate why this happens?

i`d wish there would be some fence around this or iTCO_wdt /dev/watchdog not being active after a default desktop installation.

i`d be interested if i`m the only one who thinks this is strange/dangerous behaviour.

regards
roland

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