Handle overly large answer buffers in resolver.

In EDNS0 records the maximum result size is transmitted in a 16
bit value.  Large buffer sizes were handled incorrectly by using
only the low 16 bits.  Fix this by limiting the size to 0xffff.

ChangeLog

@@ -1,3 +1,9 @@
+2009-07-16  Ulrich Drepper  <drepper@redhat.com>
+
+	[BZ #10360]
+	* resolv/res-mkquery.c (__res_nopt): If anslen is > 0xffff store
+	0xffff in the EDNS0 record.
+
 2009-07-16  Petr Baudis  <pasky@suse.cz>
 
 	* nscd/mem.c (mempool_alloc): Fix unlock missing in the else branch.

resolv/res_mkquery.c

@@ -244,7 +244,7 @@ __res_nopt(res_state statp,
 	*cp++ = 0;	/* "." */
 
 	NS_PUT16(T_OPT, cp);	/* TYPE */
-	NS_PUT16(anslen & 0xffff, cp);	/* CLASS = UDP payload size */
+	NS_PUT16(MIN(anslen, 0xffff), cp);	/* CLASS = UDP payload size */
 	*cp++ = NOERROR;	/* extended RCODE */
 	*cp++ = 0;		/* EDNS version */
 	/* XXX Once we support DNSSEC we change the flag value here.  */