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");
+		}
 	    }
 	}
     }
eed'>json-c-CVE-2020-12762.patch</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/patches/json-c-CVE-2020-12762.patch?id=f42c6bbb8e279045dbd358b25fc1d53cb1dfeeed&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-08-06 09:44:24 +0300'>2020-08-06</span></td><td><a href='/guix/commit/gnu/packages/patches/json-c-CVE-2020-12762.patch?id=10b40489742bdaa0d193c00dff1446b11c081f6a'>gnu: json-c: Fix CVE-2020-12762.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>