From: Neil Brown <neilb@suse.de>
To: Stefan Smietanowski <stesmi@stesmi.com>
Date: Sat, 13 May 2006 21:37:45 +1000
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Cc: Douglas McNaught <doug@mcnaught.org>,
       Arjan van de Ven <arjan@infradead.org>,
       Mark Rosenstand <mark@borkware.net>, linux-kernel@vger.kernel.org
Subject: Re: Executable shell scripts
In-Reply-To: message from Stefan Smietanowski on Saturday May 13
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On Saturday May 13, stesmi@stesmi.com wrote:
> > 
> > Every Unix I've ever seen works this way.  It'd be nice to have
> > unreadable executable scripts, but no one's ever done it.
> 
> The solution would be to either stick bash in the kernel (YUCK!)
> or to have the kernel basically copy the read-only script to /tmp
> or somewhere else, set permissions to sane values and
> /bin/sh /tmp/foo.a12345.

... or open the script file (which there kernel has to do anyway),
attach it to some unused fd (e.g. fd3) and pass  "/dev/fd/3" to the
interpreter rather than "/the/shell/script".

Then the interpreter doesn't need to be able to open the file for
read.

However it isn't clear that this is really a gain, as the person
running the script could use ptrace or similar to take a copy of the
script, the bypassing the missing 'r' permission.

Mind you, with ptrace, it isn't too hard to get a copy of a normal
executable that is mode '111'....

The whole concept of having files that are executable but not readable
is completely broken - it gives the appearance of protection without
the reality.

NeilBrown
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