gnu: procmail: Fix CVE-2017-16844.

* gnu/packages/patches/procmail-CVE-2017-16844.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/mail.scm (procmail)[source]: Use it.

gnu/packages/patches/procmail-CVE-2017-16844.patch

@@ -0,0 +1,25 @@
+Fix CVE-2017-16844:
+
+https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-16844
+https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876511
+
+Patch copied from Debian procmail package 3.22-26:
+
+http://http.debian.net/debian/pool/main/p/procmail/procmail_3.22-26.debian.tar.xz
+
+From: Santiago Vila <sanvila@debian.org>
+Subject: Fix heap-based buffer overflow in loadbuf()
+Bug-Debian: http://bugs.debian.org/876511
+X-Debian-version: 3.22-26
+
+--- a/src/formisc.c
++++ b/src/formisc.c
+@@ -103,7 +103,7 @@
+ }
+ 							    /* append to buf */
+ void loadbuf(text,len)const char*const text;const size_t len;
+-{ if(buffilled+len>buflen)			  /* buf can't hold the text */
++{ while(buffilled+len>buflen)			  /* buf can't hold the text */
+      buf=realloc(buf,buflen+=Bsize);
+   tmemmove(buf+buffilled,text,len);buffilled+=len;
+ }