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Re: mkdir when target exists and is a broken symlink


From: Paul Eggert
Subject: Re: mkdir when target exists and is a broken symlink
Date: Fri, 20 May 2005 13:37:19 -0700
User-agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.4 (gnu/linux)

>>POSIX requires this, but it is arguably a misfeature, due to the
>>security issues mentioned.
>
> I still don't understand how this is a security issue any more than the
> whole concept of symbolic links is a security issue.

Yes, that's the problem basically.  If you're about to say "touch /tmp/foo"
an attacker can do "ln -s /victim/.newsrc /tmp/foo".

> I'll wait for a newer coreutils release, and instead of using 'mkdir -p'
> as the standard way of trying hard to make a directory, use instead
> 'mkdir -p `readlink -f`'.

Given what you said that you wanted, you might prefer -m instead.  And
you might want to quote things (to protect against link expansions
with shell metacharacters), and protect against file names or link
expansions with leading "-".  Something like this, perhaps:

mkdir -p -- "$(readlink -m -- "$file")"




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