Fix CVE-2016-6318.

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-6318

Patch copied from Red Hat:

https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2016-6318
https://bugzilla.redhat.com/attachment.cgi?id=1188599&action=diff

It is not safe to pass words longer than STRINGSIZE further to cracklib
so the longbuffer cannot be longer than STRINGSIZE.
diff -up cracklib-2.9.0/lib/fascist.c.longgecos cracklib-2.9.0/lib/fascist.c
--- cracklib-2.9.0/lib/fascist.c.longgecos	2014-02-06 16:03:59.000000000 +0100
+++ cracklib-2.9.0/lib/fascist.c	2016-08-08 12:05:40.279235815 +0200
@@ -515,7 +515,7 @@ FascistGecosUser(char *password, const c
     char gbuffer[STRINGSIZE];
     char tbuffer[STRINGSIZE];
     char *uwords[STRINGSIZE];
-    char longbuffer[STRINGSIZE * 2];
+    char longbuffer[STRINGSIZE];
 
     if (gecos == NULL)
 	gecos = "";
@@ -596,38 +596,47 @@ FascistGecosUser(char *password, const c
     {
 	for (i = 0; i < j; i++)
 	{
-	    strcpy(longbuffer, uwords[i]);
-	    strcat(longbuffer, uwords[j]);
-
-	    if (GTry(longbuffer, password))
+	    if (strlen(uwords[i]) + strlen(uwords[j]) < STRINGSIZE)
 	    {
-		return _("it is derived from your password entry");
-	    }
-
-	    strcpy(longbuffer, uwords[j]);
-	    strcat(longbuffer, uwords[i]);
+		strcpy(longbuffer, uwords[i]);
+		strcat(longbuffer, uwords[j]);
 
-	    if (GTry(longbuffer, password))
-	    {
-		return _("it's derived from your password entry");
+		if (GTry(longbuffer, password))
+		{
+		    return _("it is derived from your password entry");
+		}
+
+		strcpy(longbuffer, uwords[j]);
+		strcat(longbuffer, uwords[i]);
+
+		if (GTry(longbuffer, password))
+		{
+		   return _("it's derived from your password entry");
+		}
 	    }
 
-	    longbuffer[0] = uwords[i][0];
-	    longbuffer[1] = '\0';
-	    strcat(longbuffer, uwords[j]);
-
-	    if (GTry(longbuffer, password))
+	    if (strlen(uwords[j]) < STRINGSIZE - 1)
 	    {
-		return _("it is derivable from your password entry");
+		longbuffer[0] = uwords[i][0];
+		longbuffer[1] = '\0';
+		strcat(longbuffer, uwords[j]);
+
+		if (GTry(longbuffer, password))
+		{
+		    return _("it is derivable from your password entry");
+		}
 	    }
 
-	    longbuffer[0] = uwords[j][0];
-	    longbuffer[1] = '\0';
-	    strcat(longbuffer, uwords[i]);
-
-	    if (GTry(longbuffer, password))
+	    if (strlen(uwords[i]) < STRINGSIZE - 1)
 	    {
-		return _("it's derivable from your password entry");
+		longbuffer[0] = uwords[j][0];
+		longbuffer[1] = '\0';
+		strcat(longbuffer, uwords[i]);
+
+		if (GTry(longbuffer, password))
+		{
+		    return _("it's derivable from your password entry");
+		}
 	    }
 	}
     }
2 to
optional.
* README: Ditto.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-01-01 18:21:55 +0100'>2018-01-01</span></td><td><a href='/guix/commit/README?id=397cd9cc416c677e84fb4bb6efef5f99d1d2394f'>doc: Update requirements in 'README'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* README (Requirements): Update.
</span></span></td><td>Mathieu Lirzin</td></tr>
<tr><td><span title='2017-09-25 00:12:49 +0200'>2017-09-25</span></td><td><a href='/guix/commit/README?id=e8d8ecde04a988f04642d754eccc16a14e0cdc53'>README: Replace http:// with https:// where applicable.</a></td><td>Marius Bakke</td></tr>