[5041] in bugtraq
Re: request-route
daemon@ATHENA.MIT.EDU (Zoltan Hidvegi)
Tue Jul 29 14:22:31 1997
Date: Tue, 29 Jul 1997 01:16:42 -0400
Reply-To: Zoltan Hidvegi <hzoli@FRONTIERNET.NET>
From: Zoltan Hidvegi <hzoli@FRONTIERNET.NET>
X-To: ariel@FIREBALL.TAU.AC.IL
To: BUGTRAQ@NETSPACE.ORG
In-Reply-To: <Pine.LNX.3.95.970726074146.17537A-100000@fireball.tau.ac.il>
from Ariel Biener at "Jul 26, 97 07:50:13 am"
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
