Date: Tue, 22 Jun 1999 23:34:21 +0930 (CST) From: Kris Kennaway <kkennawa@physics.adelaide.edu.au> To: "Brian F. Feldman" <green@unixhelp.org> Cc: hackers@freebsd.org Subject: Re: cvs commit: src/sys/kern imgact_gzip.c Message-ID: <Pine.OSF.4.10.9906222318080.28183-200000@bragg> In-Reply-To: <Pine.BSF.4.10.9906220107400.60297-200000@janus.syracuse.net>
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On Tue, 22 Jun 1999, Brian F. Feldman wrote:
> Date: Tue, 22 Jun 1999 01:08:04 -0400 (EDT)
> From: Brian F. Feldman <green@unixhelp.org>
> To: Kris Kennaway <kkennawa@physics.adelaide.edu.au>
> Cc: Peter Wemm <peter@netplex.com.au>, Jean-Marc Zucconi <jmz@freebsd.org>,
hoek@freebsd.org, cvs-committers@freebsd.org, cvs-all@freebsd.org
> Subject: Re: cvs commit: src/sys/kern imgact_gzip.c
>
> On Tue, 22 Jun 1999, Kris Kennaway wrote:
>
> > On Tue, 22 Jun 1999, Peter Wemm wrote:
> >
> > > Ahh yes, I forgot that / was read-write for MFS boots. However:
> > >
> > > #!/bin/sh
> > > skip=18
> > > if /usr/bin/tail +$skip $0 | gzip -cd > /tmp/gztmp$$; then
> > > chmod 700 /tmp/gztmp$$
> > > prog="`echo $0 | sed 's|^.*/||'`"
> > > if /bin/ln /tmp/gztmp$$ "/tmp/$prog" 2>/dev/null; then
> > > trap '/bin/rm -f /tmp/gztmp$$ "/tmp/$prog"; exit $res' 0
> > > (/bin/sleep 5; /bin/rm -f /tmp/gztmp$$ "/tmp/$prog") 2>/dev/null &
> > > /tmp/"$prog" ${1+"$@"}; res=$?
> > > else
> > > trap '/bin/rm -f /tmp/gztmp$$; exit $res' 0
> > > (/bin/sleep 5; /bin/rm -f /tmp/gztmp$$) 2>/dev/null &
> > > /tmp/gztmp$$ ${1+"$@"}; res=$?
> > > fi
> > > else
> > > echo Cannot decompress $0; exit 1
> > > fi; exit $res
> >
> > This is the unpatched (insecure) version of gzexe (all the /tmp/gztmp$$'s),
> > but it's functionally the same.
> >
> > > Now, if tail, sh, gzip, chmod, ln, sleep, rm, etc are all in the gzexe'd
> > > crunched linked binary, how is it supposed to decompress itself? "sh" itself
> > > is part of the crunched binary, so what is going to decode sh when sh itself
> > > is a shell script?
> >
> > Yes, that seems to be a problem - gzexe depends on those executables. However
> > it shouldn't be too hard to recode this decompressor in C to perform the same
> > job without any external dependencies. The question is whether that would be
> > easier than fixing the kernel to handle gzipped ELF binaries transparently -
> > almost certainly it would be.
>
> How's what I attached?
[Context left in for cross-post to hackers]
Hmm..I don't have a deflate on my system. This should be linked static as
well, otherwise you need the runtime linker + libraries, and that has a 69k
overhead (when stripped). Possibly this could be optimized further..I don't
know if this is small enough to be useful however.
Mike's suggestion of a gzipped MFS image is probably best for things like boot
floppies.
Kris
> Brian Fundakowski Feldman _ __ ___ ____ ___ ___ ___
> green@FreeBSD.org _ __ ___ | _ ) __| \
> FreeBSD: The Power to Serve! _ __ | _ \._ \ |) |
> http://www.FreeBSD.org/ _ |___/___/___/
>
-----
"Never criticize anybody until you have walked a mile in their shoes,
because by that time you will be a mile away and have their shoes."
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