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Subject: Re: Security question: "Text file busy" overwriting executables but
To: viro@math.psu.edu (Alexander Viro)
Date: Thu, 4 Oct 2001 21:39:46 +0100 (BST)
Cc: torvalds@transmeta.com (Linus Torvalds), linux-kernel@vger.kernel.org
In-Reply-To: <Pine.GSO.4.21.0110040142270.26177-100000@weyl.math.psu.edu> from "Alexander Viro" at Oct 04, 2001 01:44:57 AM
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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
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> On Thu, 4 Oct 2001, Linus Torvalds wrote:
> 
> > The reason the kernel refuses to honour it, is that MAP_DENYWRITE is an
> > excellent DoS-vehicle - you just mmap("/etc/passwd") with MAP_DENYWRITE,
> > and even root cannot write to it.. Vary nasty.
> 
> <nit>
> I _really_ doubt that something does write() on /etc/passwd.  Create a
> file and rename it over the thing - sure, but that's it.
> </nit>

The MAP_DENYWRITE rule was added a long time ago because people found actual
workable DoS attacks
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