then create a new directory (it will fail with an error if the directory already exists)
now you can create files in this directory without having to worry about other users makeing trouble for you (they can't create symlinks in this directory)
David Lang
On Sat, 16 Apr 2005, Dave Jones wrote:
Date: Sat, 16 Apr 2005 20:57:57 -0400 From: Dave Jones <[EMAIL PROTECTED]> To: Paul Jackson <[EMAIL PROTECTED]> Cc: [EMAIL PROTECTED], git@vger.kernel.org, [EMAIL PROTECTED] Subject: Re: fix mktemp (remove mktemp ;)
On Sat, Apr 16, 2005 at 05:44:09PM -0700, Paul Jackson wrote: > Dave wrote: > > mktemp is being used here to provide randomness in the filename, > > not just a uniqueness. > > Ok - useful point. > > How about: > > t=${TMPDIR:-/usr/tmp}/gitdiff.$$.$RANDOM
pid is still predictable by watching ps output, $RANDOM is one of 32768 numbers, so it's still feasable to predict the result. $RANDOM$RANDOM is better, and gets a little closer to mktemp strength randomness.
> > all an attacker has to do is create 65535 symlinks in /usr/tmp > And how about if I removed the tmp files at the top: > > t=${TMPDIR:-/usr/tmp}/gitdiff.$$.$RANDOM > trap 'rm -fr $t.?; trap 0; exit 0' 0 1 2 3 15 > rm -fr $t.? > > ... rest of script ...
Racy, though the chance of creating x thousand symlinks in such a small window probably makes it a non-issue.
Actually.. http://www.linuxsecurity.com/content/view/115462/151/ has some interesting bits on temp dir creation without mktemp. See section 3.4 onwards.
Dave
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