ebt_vlan.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * Description: EBTables 802.1Q match extension kernelspace module.
  4 * Authors: Nick Fedchik <nick@fedchik.org.ua>
  5 *          Bart De Schuymer <bdschuym@pandora.be>
  6 */
  7
  8#include <linux/if_ether.h>
  9#include <linux/if_vlan.h>
 10#include <linux/module.h>
 11#include <linux/moduleparam.h>
 12#include <linux/netfilter/x_tables.h>
 13#include <linux/netfilter_bridge/ebtables.h>
 14#include <linux/netfilter_bridge/ebt_vlan.h>
 15
 16#define MODULE_VERS "0.6"
 17
 18MODULE_AUTHOR("Nick Fedchik <nick@fedchik.org.ua>");
 19MODULE_DESCRIPTION("Ebtables: 802.1Q VLAN tag match");
 20MODULE_LICENSE("GPL");
 21
 22#define GET_BITMASK(_BIT_MASK_) info->bitmask & _BIT_MASK_
 23#define EXIT_ON_MISMATCH(_MATCH_,_MASK_) {if (!((info->_MATCH_ == _MATCH_)^!!(info->invflags & _MASK_))) return false; }
 24
 25static bool
 26ebt_vlan_mt(const struct sk_buff *skb, struct xt_action_param *par)
 27{
 28	const struct ebt_vlan_info *info = par->matchinfo;
 29
 30	unsigned short TCI;	/* Whole TCI, given from parsed frame */
 31	unsigned short id;	/* VLAN ID, given from frame TCI */
 32	unsigned char prio;	/* user_priority, given from frame TCI */
 33	/* VLAN encapsulated Type/Length field, given from orig frame */
 34	__be16 encap;
 35
 36	if (skb_vlan_tag_present(skb)) {
 37		TCI = skb_vlan_tag_get(skb);
 38		encap = skb->protocol;
 39	} else {
 40		const struct vlan_hdr *fp;
 41		struct vlan_hdr _frame;
 42
 43		fp = skb_header_pointer(skb, 0, sizeof(_frame), &_frame);
 44		if (fp == NULL)
 45			return false;
 46
 47		TCI = ntohs(fp->h_vlan_TCI);
 48		encap = fp->h_vlan_encapsulated_proto;
 49	}
 50
 51	/* Tag Control Information (TCI) consists of the following elements:
 52	 * - User_priority. The user_priority field is three bits in length,
 53	 * interpreted as a binary number.
 54	 * - Canonical Format Indicator (CFI). The Canonical Format Indicator
 55	 * (CFI) is a single bit flag value. Currently ignored.
 56	 * - VLAN Identifier (VID). The VID is encoded as
 57	 * an unsigned binary number.
 58	 */
 59	id = TCI & VLAN_VID_MASK;
 60	prio = (TCI >> 13) & 0x7;
 61
 62	/* Checking VLAN Identifier (VID) */
 63	if (GET_BITMASK(EBT_VLAN_ID))
 64		EXIT_ON_MISMATCH(id, EBT_VLAN_ID);
 65
 66	/* Checking user_priority */
 67	if (GET_BITMASK(EBT_VLAN_PRIO))
 68		EXIT_ON_MISMATCH(prio, EBT_VLAN_PRIO);
 69
 70	/* Checking Encapsulated Proto (Length/Type) field */
 71	if (GET_BITMASK(EBT_VLAN_ENCAP))
 72		EXIT_ON_MISMATCH(encap, EBT_VLAN_ENCAP);
 73
 74	return true;
 75}
 76
 77static int ebt_vlan_mt_check(const struct xt_mtchk_param *par)
 78{
 79	struct ebt_vlan_info *info = par->matchinfo;
 80	const struct ebt_entry *e = par->entryinfo;
 81
 82	/* Is it 802.1Q frame checked? */
 83	if (e->ethproto != htons(ETH_P_8021Q)) {
 84		pr_debug("passed entry proto %2.4X is not 802.1Q (8100)\n",
 85			 ntohs(e->ethproto));
 86		return -EINVAL;
 87	}
 88
 89	/* Check for bitmask range
 90	 * True if even one bit is out of mask
 91	 */
 92	if (info->bitmask & ~EBT_VLAN_MASK) {
 93		pr_debug("bitmask %2X is out of mask (%2X)\n",
 94			 info->bitmask, EBT_VLAN_MASK);
 95		return -EINVAL;
 96	}
 97
 98	/* Check for inversion flags range */
 99	if (info->invflags & ~EBT_VLAN_MASK) {
100		pr_debug("inversion flags %2X is out of mask (%2X)\n",
101			 info->invflags, EBT_VLAN_MASK);
102		return -EINVAL;
103	}
104
105	/* Reserved VLAN ID (VID) values
106	 * -----------------------------
107	 * 0 - The null VLAN ID.
108	 * 1 - The default Port VID (PVID)
109	 * 0x0FFF - Reserved for implementation use.
110	 * if_vlan.h: VLAN_N_VID 4096.
111	 */
112	if (GET_BITMASK(EBT_VLAN_ID)) {
113		if (!!info->id) { /* if id!=0 => check vid range */
114			if (info->id > VLAN_N_VID) {
115				pr_debug("id %d is out of range (1-4096)\n",
116					 info->id);
117				return -EINVAL;
118			}
119			/* Note: This is valid VLAN-tagged frame point.
120			 * Any value of user_priority are acceptable,
121			 * but should be ignored according to 802.1Q Std.
122			 * So we just drop the prio flag.
123			 */
124			info->bitmask &= ~EBT_VLAN_PRIO;
125		}
126		/* Else, id=0 (null VLAN ID)  => user_priority range (any?) */
127	}
128
129	if (GET_BITMASK(EBT_VLAN_PRIO)) {
130		if ((unsigned char) info->prio > 7) {
131			pr_debug("prio %d is out of range (0-7)\n",
132				 info->prio);
133			return -EINVAL;
134		}
135	}
136	/* Check for encapsulated proto range - it is possible to be
137	 * any value for u_short range.
138	 * if_ether.h:  ETH_ZLEN        60   -  Min. octets in frame sans FCS
139	 */
140	if (GET_BITMASK(EBT_VLAN_ENCAP)) {
141		if ((unsigned short) ntohs(info->encap) < ETH_ZLEN) {
142			pr_debug("encap frame length %d is less than "
143				 "minimal\n", ntohs(info->encap));
144			return -EINVAL;
145		}
146	}
147
148	return 0;
149}
150
151static struct xt_match ebt_vlan_mt_reg __read_mostly = {
152	.name		= "vlan",
153	.revision	= 0,
154	.family		= NFPROTO_BRIDGE,
155	.match		= ebt_vlan_mt,
156	.checkentry	= ebt_vlan_mt_check,
157	.matchsize	= sizeof(struct ebt_vlan_info),
158	.me		= THIS_MODULE,
159};
160
161static int __init ebt_vlan_init(void)
162{
163	pr_debug("ebtables 802.1Q extension module v" MODULE_VERS "\n");
164	return xt_register_match(&ebt_vlan_mt_reg);
165}
166
167static void __exit ebt_vlan_fini(void)
168{
169	xt_unregister_match(&ebt_vlan_mt_reg);
170}
171
172module_init(ebt_vlan_init);
173module_exit(ebt_vlan_fini);