gnu: freetype: Fix CVE-2018-6942.

* gnu/packages/patches/freetype-CVE-2018-6942.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/fontutils.scm (freetype)[replacement]: New field.
(freetype/fixed): New variable.

gnu/local.mk

@@ -655,6 +655,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/freeimage-CVE-2015-0852.patch		\
   %D%/packages/patches/freeimage-CVE-2016-5684.patch		\
   %D%/packages/patches/freeimage-fix-build-with-gcc-5.patch	\
+  %D%/packages/patches/freetype-CVE-2018-6942.patch		\
   %D%/packages/patches/fuse-overlapping-headers.patch				\
   %D%/packages/patches/gawk-shell.patch				\
   %D%/packages/patches/gcc-arm-bug-71399.patch			\

gnu/packages/fontutils.scm

@@ -54,6 +54,7 @@
   (package
    (name "freetype")
    (version "2.8.1")
+   (replacement freetype/fixed)
    (source (origin
             (method url-fetch)
             (uri (string-append "mirror://savannah/freetype/freetype-"
@@ -78,6 +79,13 @@ anti-aliased glyph bitmap generation with 256 gray levels.")
    (license license:freetype)           ; some files have other licenses
    (home-page "https://www.freetype.org/")))
 
+(define freetype/fixed
+  (package/inherit freetype
+                   (source
+                    (origin
+                      (inherit (package-source freetype))
+                      (patches (search-patches "freetype-CVE-2018-6942.patch"))))))
+
 (define-public ttfautohint
   (package
     (name "ttfautohint")

gnu/packages/patches/freetype-CVE-2018-6942.patch

@@ -0,0 +1,31 @@
+Fix CVE-2018-6942:
+
+https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-6942
+https://people.canonical.com/~ubuntu-security/cve/2018/CVE-2018-6942.html
+
+Copied from upstream (ChangeLog section removed):
+https://git.savannah.gnu.org/cgit/freetype/freetype2.git/commit/?id=29c759284e305ec428703c9a5831d0b1fc3497ef
+
+diff --git a/src/truetype/ttinterp.c b/src/truetype/ttinterp.c
+index d855aaa..551f14a 100644
+--- a/src/truetype/ttinterp.c
++++ b/src/truetype/ttinterp.c
+@@ -7532,8 +7532,16 @@
+       return;
+     }
+ 
+-    for ( i = 0; i < num_axes; i++ )
+-      args[i] = coords[i] >> 2; /* convert 16.16 to 2.14 format */
++    if ( coords )
++    {
++      for ( i = 0; i < num_axes; i++ )
++        args[i] = coords[i] >> 2; /* convert 16.16 to 2.14 format */
++    }
++    else
++    {
++      for ( i = 0; i < num_axes; i++ )
++        args[i] = 0;
++    }
+   }
+ 
+