.desktop file security

Patryk Zawadzki patrys at pld-linux.org
Wed Feb 25 00:29:55 PST 2009

On Wed, Feb 25, 2009 at 2:13 AM, Michael Pyne <mpyne at purinchu.net> wrote:
> On Tuesday 24 February 2009, Patryk Zawadzki wrote:
>> Also using extended filesystem attributes (or some other metadata
>> storage) gives you the additional protection from "downloaded a
>> tarball / uncompressed to desktop / the file was compressed as
>> executable / now I have two computer icons" kind of scenarios.
> So what happens when the archive extractor actually supports xattr and now
> there is executable-with-fancy bit trojan laying in the directory?

It's safe to strip all the xattrs (by cooperating with the desktop's
archiving tool of choice maintainers) without sacrificing any
functionality. Scripts will continue to work, binaries will behave as
they should. The only difference is clicking some of them will yield a
"possibly unsafe content" warning. It's not safe to do the same thing
with the +x flag as you'll break most of the source code tarballs.
Thus +x/-x is not likely to work in a more generic case (not .desktop
file specific).

Also relying on just the +x flag will not work in collaborative
environments. If I'm the file owner I get to control the +x flag. In
such cases we still need an external metadata storage to take note of
the file path, its hash (to detect changes) and whether it was trusted
or not and if we implement such storage, why not allow just any other
attributes (thus having a working xattrs fallback even if no
filesystem support is present).

Patryk Zawadzki

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