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Re: request-route
From: hzoli () FRONTIERNET NET (Zoltan Hidvegi)
Date: Tue, 29 Jul 1997 01:16:42 -0400


Ariel Biener wrote:
[...]
/sbin/request-route is a script. So, the script can be fixed to check for
the lock file, or whatever other security check are needed. No need to
just go and remove before finding a suitable solution.

 A simple solution would be to add a:

        set -o noclobber

In the script, right here:

        sleep 60 &
        sleepid=$!
--->    set -o noclobber
        echo $sleepid > $LOCK
        wait $sleepid

Unfortunately this is still not enough.  The problem is that many (if not
most) shells do not implement noclobber in a race-free way, but even if
they do, noclobber still allows writing to device special files, so a
symlink to /dev/hda will be followed by the shell destroying your master
boot record.  As far as I know, there is no portable way to safely create
lock files in a world-writable directory from a bourne-shell script.

If the script runs as root (as it is the case with request-route), it is
enough to put the lockfile in a directory writable only by root.  Debian
uses /var/run for the request-route lockfile.

Zoltan



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