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Date: Mon, 24 Nov 2003 16:25:37 -0200
From: Bruno Lustosa <>
Subject: Re: hard links on Linux create local DoS vulnerability and security problems

* Jakob Lell <> [24-11-2003 16:11]:
> Furthermore, users can even create links to a setuid binary. If there is a 
> security whole like a buffer overflow in any setuid binary, a cracker can 
> create a hard link to this file in his home directory. This link still exists 
> when the administrator has fixed the security whole by removing or replacing 
> the insecure program. This makes it possible for a cracker to keep a security 
> whole open until an exploit is available. It is even possible to create links 
> to every setuid program on the system. This doesn't create new security 
> wholes but makes it more likely that they are exploited.

Just checked this on 2.6.0-test9, and it will not work.
When you create a hard link to a setuid or any other file, it will
inherit the same owner and mode of the original. However, if the
original file is changed (owner, group, mode, or content), the link will
reflect those changes as well.

Bruno Lustosa, aka Lofofora          | Email:
Network Administrator/Web Programmer | ICQ UIN: 1406477
Rio de Janeiro - Brazil              |

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