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Date: Sat, 20 Oct 2018 11:42:20 +0000
From: Jordan Glover <Golden_Miller83@...tonmail.ch>
To: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com>
Subject: Re: Attempting to patch ghostscript-9.25
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, October 20, 2018 3:47 AM, Ken Moffat <zarniwhoop@...world.com> wrote:
> Hi,
>
> I hope people can read this - I know that google marks my mails as
> spam (so no point Cc'ing Tavis) and also that Suse discard my mails.
> Probably many other places also do that. Anyway:
>
> When the first set of vulnerabilities in 9.25 came out there was a
> nice 'mostly harmless' example, and I patched BLFS for that (needed
> one extra commit beyond the two Tavis specified, so that I could
> make sense of where to apply part of it).
>
> For the later vulnerabilities, working out what to apply has been
> much harder. Either everyone else thinks that other mitigations
> against untrusted ps files will suffice, or else it's on everybody's
> ToDo lists.
>
> So, here is a first attempt to fix all this month's vulnerabilities.
> For the latest exploit(s) I do not have an example, so I don't know
> whether or not this works. But it prevents the earlier
> vulnerability, and usage of real ps (and eps - I only have the gs
> examples, and only gs seems able to use them) seems to work
> correctly. Unlike my first attempt to fix this, which turned out
> to fail to display any ps, eps files.
>
> The patch is a bit big, so I've uploaded it to
> http://www.linuxfromscratch.org/~ken/provisional/ as
> ghostscript-9.25-security_fixes-2.patch
>
> 'provisional' until I find out if it protects adequately. If there
> turn out ot be problems, I suppose I'll need to renumber later
> versions.
>
> Built in BLFS using the same instructions as for the earlier -1
> patch [ http://www.linuxfromscratch.org/blfs/view/svn/pst/gs.html ]
> but that doesn't mean it will work for everyone else's ways of
> building. Note tht I do build the shared library.
>
> The patch lists which upstream commits I pulled in. I was mostly
> concentrating on changes to gs_init which would maybe help me apply
> the needed patches. As I've noted in the patch's introduction,
> several commits had negative offsets (I guess hunks of code were
> removed in some of the unrelated commits that I ignored).
>
> Comments welcome.
>
> One final thought - apart from 9.25, upstream seem to have an
> approximately 6-monthly release schedule, so probably the only thing
> likely to speed up 9.26 is everybody patching ;)
>
> ĸen
I think the easiest way is to build on upstream git snapshot.
All of its contents will be included in future release anyway.
Jordan
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