// SPDX-License-Identifier: GPL-2.0-only
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/types.h>
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#include <linux/module.h>
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#include <net/ip.h>
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#include <linux/ipv6.h>
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#include <net/ipv6.h>
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#include <net/tcp.h>
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#include <net/udp.h>
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#include <linux/netfilter/x_tables.h>
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#include <linux/netfilter/xt_tcpudp.h>
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#include <linux/netfilter_ipv4/ip_tables.h>
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#include <linux/netfilter_ipv6/ip6_tables.h>
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MODULE_DESCRIPTION("Xtables: TCP, UDP and UDP-Lite match");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS("xt_tcp");
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MODULE_ALIAS("xt_udp");
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MODULE_ALIAS("ipt_udp");
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MODULE_ALIAS("ipt_tcp");
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MODULE_ALIAS("ip6t_udp");
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MODULE_ALIAS("ip6t_tcp");
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/* Returns 1 if the port is matched by the range, 0 otherwise */
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static inline bool
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port_match(u_int16_t min, u_int16_t max, u_int16_t port, bool invert)
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{
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return (port >= min && port <= max) ^ invert;
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}
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static bool
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tcp_find_option(u_int8_t option,
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const struct sk_buff *skb,
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unsigned int protoff,
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unsigned int optlen,
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bool invert,
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bool *hotdrop)
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{
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/* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
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const u_int8_t *op;
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u_int8_t _opt[60 - sizeof(struct tcphdr)];
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unsigned int i;
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pr_debug("finding option\n");
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if (!optlen)
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return invert;
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/* If we don't have the whole header, drop packet. */
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op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
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optlen, _opt);
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if (op == NULL) {
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*hotdrop = true;
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return false;
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}
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for (i = 0; i < optlen; ) {
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if (op[i] == option) return !invert;
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if (op[i] < 2) i++;
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else i += op[i+1]?:1;
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}
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return invert;
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}
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static bool tcp_mt(const struct sk_buff *skb, struct xt_action_param *par)
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{
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const struct tcphdr *th;
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struct tcphdr _tcph;
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const struct xt_tcp *tcpinfo = par->matchinfo;
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if (par->fragoff != 0) {
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/* To quote Alan:
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Don't allow a fragment of TCP 8 bytes in. Nobody normal
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causes this. Its a cracker trying to break in by doing a
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flag overwrite to pass the direction checks.
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*/
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if (par->fragoff == 1) {
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pr_debug("Dropping evil TCP offset=1 frag.\n");
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par->hotdrop = true;
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}
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/* Must not be a fragment. */
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return false;
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}
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th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
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if (th == NULL) {
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/* We've been asked to examine this packet, and we
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can't. Hence, no choice but to drop. */
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pr_debug("Dropping evil TCP offset=0 tinygram.\n");
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par->hotdrop = true;
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return false;
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}
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if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
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ntohs(th->source),
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!!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
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return false;
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if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
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ntohs(th->dest),
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!!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
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return false;
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if (!NF_INVF(tcpinfo, XT_TCP_INV_FLAGS,
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(((unsigned char *)th)[13] & tcpinfo->flg_mask) == tcpinfo->flg_cmp))
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return false;
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if (tcpinfo->option) {
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if (th->doff * 4 < sizeof(_tcph)) {
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par->hotdrop = true;
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return false;
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}
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if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
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th->doff*4 - sizeof(_tcph),
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tcpinfo->invflags & XT_TCP_INV_OPTION,
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&par->hotdrop))
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return false;
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}
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return true;
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}
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static int tcp_mt_check(const struct xt_mtchk_param *par)
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{
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const struct xt_tcp *tcpinfo = par->matchinfo;
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/* Must specify no unknown invflags */
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return (tcpinfo->invflags & ~XT_TCP_INV_MASK) ? -EINVAL : 0;
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}
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static bool udp_mt(const struct sk_buff *skb, struct xt_action_param *par)
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{
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const struct udphdr *uh;
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struct udphdr _udph;
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const struct xt_udp *udpinfo = par->matchinfo;
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/* Must not be a fragment. */
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if (par->fragoff != 0)
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return false;
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uh = skb_header_pointer(skb, par->thoff, sizeof(_udph), &_udph);
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if (uh == NULL) {
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/* We've been asked to examine this packet, and we
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can't. Hence, no choice but to drop. */
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pr_debug("Dropping evil UDP tinygram.\n");
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par->hotdrop = true;
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return false;
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}
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return port_match(udpinfo->spts[0], udpinfo->spts[1],
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ntohs(uh->source),
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!!(udpinfo->invflags & XT_UDP_INV_SRCPT))
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&& port_match(udpinfo->dpts[0], udpinfo->dpts[1],
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ntohs(uh->dest),
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!!(udpinfo->invflags & XT_UDP_INV_DSTPT));
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}
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static int udp_mt_check(const struct xt_mtchk_param *par)
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{
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const struct xt_udp *udpinfo = par->matchinfo;
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/* Must specify no unknown invflags */
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return (udpinfo->invflags & ~XT_UDP_INV_MASK) ? -EINVAL : 0;
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}
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static struct xt_match tcpudp_mt_reg[] __read_mostly = {
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{
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.name = "tcp",
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.family = NFPROTO_IPV4,
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.checkentry = tcp_mt_check,
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.match = tcp_mt,
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.matchsize = sizeof(struct xt_tcp),
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.proto = IPPROTO_TCP,
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.me = THIS_MODULE,
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},
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{
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.name = "tcp",
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.family = NFPROTO_IPV6,
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.checkentry = tcp_mt_check,
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.match = tcp_mt,
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.matchsize = sizeof(struct xt_tcp),
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.proto = IPPROTO_TCP,
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.me = THIS_MODULE,
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},
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{
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.name = "udp",
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.family = NFPROTO_IPV4,
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.checkentry = udp_mt_check,
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.match = udp_mt,
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.matchsize = sizeof(struct xt_udp),
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.proto = IPPROTO_UDP,
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.me = THIS_MODULE,
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},
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{
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.name = "udp",
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.family = NFPROTO_IPV6,
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.checkentry = udp_mt_check,
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.match = udp_mt,
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.matchsize = sizeof(struct xt_udp),
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.proto = IPPROTO_UDP,
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.me = THIS_MODULE,
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},
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{
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.name = "udplite",
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.family = NFPROTO_IPV4,
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.checkentry = udp_mt_check,
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.match = udp_mt,
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.matchsize = sizeof(struct xt_udp),
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.proto = IPPROTO_UDPLITE,
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.me = THIS_MODULE,
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},
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{
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.name = "udplite",
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.family = NFPROTO_IPV6,
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.checkentry = udp_mt_check,
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.match = udp_mt,
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.matchsize = sizeof(struct xt_udp),
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.proto = IPPROTO_UDPLITE,
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.me = THIS_MODULE,
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},
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};
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static int __init tcpudp_mt_init(void)
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{
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return xt_register_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
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}
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static void __exit tcpudp_mt_exit(void)
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{
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xt_unregister_matches(tcpudp_mt_reg, ARRAY_SIZE(tcpudp_mt_reg));
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}
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module_init(tcpudp_mt_init);
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module_exit(tcpudp_mt_exit);
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