still getting DNS poisioning I think - some spam appearing from sites which
appear to have domains when the spam arrives but which has disappeared
when I look later. Iven if I am missunderstanding the problem this is a
more complete fix.

Notes:
Mon Apr 10 11:44:42 EDT 2006 rsc
Mon Apr 10 11:58:51 EDT 2006 rsc
    It's entirely possible that the spammer has control of
    a dns server and simply creates a name, sends the mail,
    and then deletes the name.  Easy enough and nothing you
    can do about it.
    
    That said, the norecursion flag is really just a clumsy
    hack around the fact that the Plan 9 dns server accepts
    glue records indiscriminately from anyone.
    
    See http://ketil.froyn.name/poison.html for a good 
    description and demonstration.
    
    cpu% ndb/dnsquery
    > bad.ketil.froyn.name ns
    bad.ketil.froyn.name ns	www.example.com
    > www.example.com ip
    www.example.com ip	217.144.230.29
    > ^D
    cpu% 
    
    That's wrong.  The www.example.com glue record
    in the bad.ketil.froyn.name ns lookup should have
    been ignored.
    
    I would be very happy if someone would fix this.
    
    Thanks.
    Russ


Reference: /n/sources/patch/applied/dnstcp-norecursion
Date: Sun Apr  9 20:52:27 CES 2006
Signed-off-by: steve@quintile.net
Reviewed-by: rsc

--- /sys/src/cmd/ndb/dnstcp.c	Sun Apr  9 20:50:55 2006
+++ /sys/src/cmd/ndb/dnstcp.c	Sun Apr  9 20:50:52 2006
@@ -31,6 +31,13 @@
 static void	refreshmain(char*);
 
 void
+usage(void)
+{
+	fprint(2, "usage: %s [-rR] [-f ndb-file] [-x netmtpt]\n", argv0);
+	exits("usage");
+}
+
+void
 main(int argc, char *argv[])
 {
 	int len;
@@ -42,6 +49,9 @@
 	char *ext = "";
 
 	ARGBEGIN{
+	case 'R':
+		norecursion = 1;
+		break;
 	case 'd':
 		debug++;
 		break;
@@ -54,6 +64,9 @@
 	case 'x':
 		ext = ARGF();
 		break;
+	default:
+		usage();
+		break;
 	}ARGEND
 
 	if(debug < 2)
@@ -234,10 +247,12 @@
 
 	memset(repp, 0, sizeof(*repp));
 	repp->id = reqp->id;
-	repp->flags = Fauth | Fresp | Fcanrec | Oquery;
 	repp->qd = reqp->qd;
 	reqp->qd = reqp->qd->next;
 	repp->qd->next = 0;
+	repp->flags = Fauth | Fresp | Oquery;
+	if(!norecursion)
+		repp->flags |= Fcanrec;
 	dp = repp->qd->owner;
 
 	/* send the soa */