From: Roy Marples <roy@marples.name>
Date: Sun, 26 Feb 2017 20:33:33 +0000 (+0000)
Subject: Re-work the BPF filters so they are early return.
X-Git-Tag: v7.0.0-beta1~71
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cf742a6e98d82d9c87b4ed0a1558517e7dc5f282;p=thirdparty%2Fdhcpcd.git

Re-work the BPF filters so they are early return.
This will allow us to insert addresses of interest in the future.
---

diff --git a/bpf-filter.h b/bpf-filter.h
index 37c3e303..8cb696b1 100644
--- a/bpf-filter.h
+++ b/bpf-filter.h
@@ -1,6 +1,6 @@
 /*
  * dhcpcd - DHCP client daemon
- * Copyright (c) 2006-2008 Roy Marples <roy@marples.name>
+ * Copyright (c) 2006-2017 Roy Marples <roy@marples.name>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -30,72 +30,51 @@
 #ifndef BPF_WHOLEPACKET
 # define BPF_WHOLEPACKET ~0U
 #endif
+
 static const struct bpf_insn arp_bpf_filter [] = {
 #ifndef BPF_SKIPTYPE
 	/* Make sure this is an ARP packet... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_ARP, 0, 6),
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_ARP, 1, 0),
+	BPF_STMT(BPF_RET + BPF_K, 0),
 #endif
 	/* Make sure this is for IP ... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 16 + BPF_ETHCOOK),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 4),
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0),
+	BPF_STMT(BPF_RET + BPF_K, 0),
 	/* Make sure this is an ARP REQUEST... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20 + BPF_ETHCOOK),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REQUEST, 1, 0),
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REQUEST, 2, 0),
 	/* or ARP REPLY... */
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 0, 1),
-	/* If we passed all the tests, ask for the whole packet. */
-	BPF_STMT(BPF_RET + BPF_K, BPF_WHOLEPACKET),
-	/* Otherwise, drop it. */
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 1),
 	BPF_STMT(BPF_RET + BPF_K, 0),
+	/* Pass back the whole packet. */
+	BPF_STMT(BPF_RET + BPF_K, BPF_WHOLEPACKET),
 };
 #define arp_bpf_filter_len __arraycount(arp_bpf_filter)
 
-
-/* dhcp_bpf_filter taken from bpf.c in dhcp-3.1.0
- *
- * Copyright (c) 2004,2007 by Internet Systems Consortium, Inc. ("ISC")
- * Copyright (c) 1996-2003 by Internet Software Consortium
- *
- * Permission to use, copy, modify, and distribute this software for any
- * purpose with or without fee is hereby granted, provided that the above
- * copyright notice and this permission notice appear in all copies.
- *
- * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
- * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
- * MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR
- * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
- * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
- * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
- * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
- *
- *   Internet Systems Consortium, Inc.
- *   950 Charter Street
- *   Redwood City, CA 94063
- *   <info@isc.org>
- *   http://www.isc.org/
- */
-
 static const struct bpf_insn bootp_bpf_filter [] = {
 #ifndef BPF_SKIPTYPE
 	/* Make sure this is an IP packet... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 12),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 0, 8),
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0),
+	BPF_STMT(BPF_RET + BPF_K, 0),
 #endif
 	/* Make sure it's a UDP packet... */
 	BPF_STMT(BPF_LD + BPF_B + BPF_ABS, 23 + BPF_ETHCOOK),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 0, 6),
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 1, 0),
+	BPF_STMT(BPF_RET + BPF_K, 0),
 	/* Make sure this isn't a fragment... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_ABS, 20 + BPF_ETHCOOK),
-	BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 4, 0),
+	BPF_JUMP(BPF_JMP + BPF_JSET + BPF_K, 0x1fff, 0, 1),
+	BPF_STMT(BPF_RET + BPF_K, 0),
 	/* Get the IP header length... */
 	BPF_STMT(BPF_LDX + BPF_B + BPF_MSH, 14 + BPF_ETHCOOK),
 	/* Make sure it's to the right port... */
 	BPF_STMT(BPF_LD + BPF_H + BPF_IND, 16 + BPF_ETHCOOK),
-	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, BOOTPC, 0, 1),
-	/* If we passed all the tests, ask for the whole packet. */
-	BPF_STMT(BPF_RET + BPF_K, BPF_WHOLEPACKET),
-	/* Otherwise, drop it. */
+	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, BOOTPC, 1, 0),
 	BPF_STMT(BPF_RET + BPF_K, 0),
+	/* Pass back the whole packet. */
+	BPF_STMT(BPF_RET + BPF_K, BPF_WHOLEPACKET),
 };
 #define bootp_bpf_filter_len __arraycount(bootp_bpf_filter)