Subject: Re: [bug#36424] expat-2.2.7 for CVE-2018-20843

From: Marius Bakke <[email-masked]>
Date: Sat, 06 Jul 2019 00:53:52 +0200

Jack Hill <[email-masked]> writes:

> On Tue, 2 Jul 2019, Jack Hill wrote:
>
>>> Apparently these symbols were never supposed to be exported:
>>> <https://github.com/libexpat/libexpat/pull/197>.  However, there could
>>> be packages "in the wild" that uses these symbols and would silently
>>> break with the grafted Expat.
>>> 
>>> IIUC the fix for CVE-2018-20843 is this commit:
>>> <https://github.com/libexpat/libexpat/commit/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6>.
>>> 
>>> I think it's better to graft a variant with only this patch to be on the
>>> safe side.  Can you try that?
>>
>> Good idea. I didn't think to check. Yes, I can try to do that.
>>
>>> Could you also submit a second patch that adds GitHub as an additional
>>> download location for the regular Expat package?  :-)
>>
>> I'll try that as well.
>
> I've prepared the two attached patches that I believe implement Marius's 
> proposed solution.

Thanks!

One minor problem... the expat patch does not actually apply on our copy
of expat!  Can you look into it?

> From 4186a68b660c93b5800be8f126051da92749dc9a Mon Sep 17 00:00:00 2001
> From: Jack Hill <[email-masked]>
> Date: Thu, 4 Jul 2019 17:00:27 -0400
> Subject: [PATCH 1/2] gnu: expat: Add additional source URI
>
> The expat sourceforge page announces that the project is in the process of
> moving to GitHub.
>
> * gnu/packages/xml.scm (expat)[source]: Add GitHub URI.
> ---
>  gnu/packages/xml.scm | 39 +++++++++++++++++++++++----------------
>  1 file changed, 23 insertions(+), 16 deletions(-)

[...]
  
>  (define-public expat
> -  (package
> -    (name "expat")
> -    (version "2.2.6")
> -    (source (origin
> -             (method url-fetch)
> -             (uri (string-append "mirror://sourceforge/expat/expat/"
> -                                 version "/expat-" version ".tar.bz2"))
> -             (sha256
> -              (base32
> -               "1wl1x93b5w457ddsdgj0lh7yjq4q6l7wfbgwhagkc8fm2qkkrd0p"))))
> -    (build-system gnu-build-system)
> -    (home-page "https://libexpat.github.io/")
> -    (synopsis "Stream-oriented XML parser library written in C")
> -    (description
> -     "Expat is an XML parser library written in C.  It is a
> +  (let ((dot->underscore (lambda (c) (if (equal? #\. c) #\_ c))))
> +      (package
> +        (name "expat")
> +        (version "2.2.6")
> +        (source (origin
> +                  (method url-fetch)
> +                  (uri (list (string-append
> +                              "mirror://sourceforge/expat/expat/"
> +                              version "/expat-" version ".tar.bz2")
> +                             (string-append
> +                              "https://github.com/libexpat/libexpat/releases/download/R_"
> +                              (string-map dot->underscore version)
> +                              "/expat-" version ".tar.bz2")))
> +                  (sha256
> +                   (base32
> +                    "1wl1x93b5w457ddsdgj0lh7yjq4q6l7wfbgwhagkc8fm2qkkrd0p"))))
> +        (build-system gnu-build-system)
> +        (home-page "https://libexpat.github.io/")
> +        (synopsis "Stream-oriented XML parser library written in C")
> +        (description
> +         "Expat is an XML parser library written in C.  It is a

Can you move this let binding inside the (source ...) field?  That way
we don't have to reindent the whole thing.

> From 2f8268a0b549b9c08744d8bc05e2cf135e40be99 Mon Sep 17 00:00:00 2001
> From: Jack Hill <[email-masked]>
> Date: Thu, 4 Jul 2019 19:41:30 -0400
> Subject: [PATCH 2/2] gnu: expat: fix CVE-2018-20843.
>
> * gnu/packages/xml.scm (expat)[replacement]: New field.
> (expat/fixed): New variable.
> * gnu/packages/patches/expat-CVE-2018-20843.patch: New file.
> * gnu/local.mk (dist_patch_DATA): Add patch file.
> ---
>  gnu/local.mk                                    |  7 ++++---
>  gnu/packages/patches/expat-CVE-2018-20843.patch | 16 ++++++++++++++++
>  gnu/packages/xml.scm                            |  9 +++++++++
>  3 files changed, 29 insertions(+), 3 deletions(-)
>  create mode 100644 gnu/packages/patches/expat-CVE-2018-20843.patch
>
> diff --git a/gnu/local.mk b/gnu/local.mk
> index 6e90d88689..bcf47d7378 100644
> --- a/gnu/local.mk
> +++ b/gnu/local.mk
> @@ -764,20 +764,21 @@ dist_patch_DATA =						\
>    %D%/packages/patches/einstein-build.patch			\
>    %D%/packages/patches/emacs-exec-path.patch			\
>    %D%/packages/patches/emacs-fix-scheme-indent-function.patch	\
> -  %D%/packages/patches/emacs-json-reformat-fix-tests.patch	\
>    %D%/packages/patches/emacs-highlight-stages-add-gexp.patch	\
> +  %D%/packages/patches/emacs-json-reformat-fix-tests.patch	\
>    %D%/packages/patches/emacs-scheme-complete-scheme-r5rs-info.patch	\
>    %D%/packages/patches/emacs-source-date-epoch.patch		\
> -  %D%/packages/patches/emacs-unpackaged-req.patch		\
>    %D%/packages/patches/emacs-undohist-ignored.patch	\
> +  %D%/packages/patches/emacs-unpackaged-req.patch		\
>    %D%/packages/patches/emacs-wordnut-require-adaptive-wrap.patch	\
>    %D%/packages/patches/emacs-zones-called-interactively.patch	\
>    %D%/packages/patches/enlightenment-fix-setuid-path.patch	\
>    %D%/packages/patches/erlang-man-path.patch			\
>    %D%/packages/patches/eudev-rules-directory.patch		\
>    %D%/packages/patches/evilwm-lost-focus-bug.patch		\
> -  %D%/packages/patches/exiv2-CVE-2017-14860.patch		\
>    %D%/packages/patches/exiv2-CVE-2017-14859-14862-14864.patch	\
> +  %D%/packages/patches/exiv2-CVE-2017-14860.patch		\
> +  %D%/packages/patches/expat-CVE-2018-20843.patch		\

You addressed this in another email, and I do think we should try to
avoid needless moving around of these lines.  There are enough merge
conflicts on this file as-is, no need to introduce artificial ones.  :-)

>    %D%/packages/patches/extundelete-e2fsprogs-1.44.patch		\
>    %D%/packages/patches/fastcap-mulGlobal.patch			\
>    %D%/packages/patches/fastcap-mulSetup.patch			\
> diff --git a/gnu/packages/patches/expat-CVE-2018-20843.patch b/gnu/packages/patches/expat-CVE-2018-20843.patch
> new file mode 100644
> index 0000000000..dd64b91965
> --- /dev/null
> +++ b/gnu/packages/patches/expat-CVE-2018-20843.patch
> @@ -0,0 +1,16 @@
> +Fix extraction of namespace prefix from XML name.
> +Fixes CVE-2018-20843
> +
> +diff --git a/expat/lib/xmlparse.c b/expat/lib/xmlparse.c
> +index 30d55c5..737d7cd 100644
> +--- a/expat/lib/xmlparse.c
> ++++ b/expat/lib/xmlparse.c
         ^^^^^^
It looks like this has to be removed from the patch file.  Could you
also add a link to the upstream commit for reference?

It's also good practice to provide an URL to the MITRE CVE page:
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-20843>.

Thanks for working on this!  :-)