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

[Jack Hill <jackhill@jackhill.us>]

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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,
Jack

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From 4186a68b660c93b5800be8f126051da92749dc9a Mon Sep 17 00:00:00 2001
From: Jack Hill <jackhill@jackhill.us>
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(-)

diff --git a/gnu/packages/xml.scm b/gnu/packages/xml.scm
index fc60758724..dab6597690 100644
--- a/gnu/packages/xml.scm
+++ b/gnu/packages/xml.scm
@@ -20,6 +20,7 @@
 ;;; Copyright © 2017 Petter <petter@mykolab.ch>
 ;;; Copyright © 2017 Stefan Reichör <stefan@xsteve.at>
 ;;; Copyright © 2018 Pierre Neidhardt <mail@ambrevar.xyz>
+;;; Copyright © 2019 Jack Hill <jackhill@jackhill.us>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -63,24 +64,30 @@
   #:use-module (gnu packages pkg-config))
 
 (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
 stream-oriented parser in which an application registers handlers for
 things the parser might find in the XML document (like start tags).")
-    (license license:expat)))
+        (license license:expat))))
 
 (define-public libebml
   (package
-- 
2.22.0


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From 2f8268a0b549b9c08744d8bc05e2cf135e40be99 Mon Sep 17 00:00:00 2001
From: Jack Hill <jackhill@jackhill.us>
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		\
   %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
+@@ -6071,7 +6071,7 @@ setElementTypePrefix(XML_Parser parser, ELEMENT_TYPE *elementType)
+       else
+         poolDiscard(&dtd->pool);
+       elementType->prefix = prefix;
+-
++      break;
+     }
+   }
+   return 1;
diff --git a/gnu/packages/xml.scm b/gnu/packages/xml.scm
index dab6597690..8c289c5cbe 100644
--- a/gnu/packages/xml.scm
+++ b/gnu/packages/xml.scm
@@ -67,6 +67,7 @@
   (let ((dot->underscore (lambda (c) (if (equal? #\. c) #\_ c))))
       (package
         (name "expat")
+        (replacement expat/fixed)
         (version "2.2.6")
         (source (origin
                   (method url-fetch)
@@ -89,6 +90,14 @@ stream-oriented parser in which an application registers handlers for
 things the parser might find in the XML document (like start tags).")
         (license license:expat))))
 
+(define expat/fixed
+  (package
+    (inherit expat)
+    (source
+     (origin
+       (inherit (package-source expat))
+       (patches (search-patches "expat-CVE-2018-20843.patch"))))))
+
 (define-public libebml
   (package
     (name "libebml")
-- 
2.22.0