gnu: libexif: Fix CVE-2017-7544.

* gnu/packages/patches/libexif-CVE-2017-7544.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/photo.scm (feh)[source]: Use it.

gnu/local.mk

@@ -805,6 +805,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/libevent-2.0-evbuffer-add-use-last-with-datap.patch	\
   %D%/packages/patches/libevent-2.1-dns-tests.patch		\
   %D%/packages/patches/libevent-2.1-skip-failing-test.patch	\
+  %D%/packages/patches/libexif-CVE-2017-7544.patch		\
   %D%/packages/patches/libgit2-0.25.1-mtime-0.patch		\
   %D%/packages/patches/libgdata-fix-tests.patch			\
   %D%/packages/patches/libgdata-glib-duplicate-tests.patch	\

gnu/packages/patches/libexif-CVE-2017-7544.patch

@@ -0,0 +1,29 @@
+Fix CVE-2017-7544:
+
+https://sourceforge.net/p/libexif/bugs/130/
+https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7544
+
+Patch copied from upstream bug tracker:
+
+https://sourceforge.net/p/libexif/bugs/130/#489a
+
+Index: libexif/exif-data.c
+===================================================================
+RCS file: /cvsroot/libexif/libexif/libexif/exif-data.c,v
+retrieving revision 1.131
+diff -u -r1.131 exif-data.c
+--- a/libexif/exif-data.c	12 Jul 2012 17:28:26 -0000	1.131
++++ b/libexif/exif-data.c	25 Jul 2017 21:34:06 -0000
+@@ -255,6 +255,12 @@
+ 			exif_mnote_data_set_offset (data->priv->md, *ds - 6);
+ 			exif_mnote_data_save (data->priv->md, &e->data, &e->size);
+ 			e->components = e->size;
++			if (exif_format_get_size (e->format) != 1) {
++				/* e->format is taken from input code,
++				 * but we need to make sure it is a 1 byte
++				 * entity due to the multiplication below. */
++				e->format = EXIF_FORMAT_UNDEFINED;
++			}
+ 		}
+ 	}
+ 

gnu/packages/photo.scm

@@ -28,6 +28,7 @@ (define-module (gnu packages photo)
   #:use-module ((guix licenses) #:prefix license:)
   #:use-module (guix packages)
   #:use-module (guix utils)
+  #:use-module (gnu packages)
   #:use-module (gnu packages algebra)
   #:use-module (gnu packages autotools)
   #:use-module (gnu packages base)
@@ -89,6 +90,7 @@ (define-public libexif
               (method url-fetch)
               (uri (string-append "mirror://sourceforge/libexif/libexif/"
                                   version "/libexif-" version ".tar.bz2"))
+              (patches (search-patches "libexif-CVE-2017-7544.patch"))
               (sha256
                (base32
                 "06nlsibr3ylfwp28w8f5466l6drgrnydgxrm4jmxzrmk5svaxk8n"))))