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/* Shared library add-on to iptables to add TCP support. */
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#include <linux/netfilter_ipv4/ip_tables.h>
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/* Function which prints out usage message. */
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" --tcp-flags [!] mask comp match when TCP flags & mask == comp\n"
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" (Flags: SYN ACK FIN RST URG PSH ALL NONE)\n"
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"[!] --syn match when only SYN flag set\n"
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" (equivalent to --tcp-flags SYN,RST,ACK SYN)\n"
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" --source-port [!] port[:port]\n"
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" match source port(s)\n"
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" --destination-port [!] port[:port]\n"
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" match destination port(s)\n"
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" --tcp-option [!] number match if TCP option set\n\n",
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static struct option opts[] = {
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{ "source-port", 1, 0, '1' },
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{ "sport", 1, 0, '1' }, /* synonym */
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{ "destination-port", 1, 0, '2' },
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{ "dport", 1, 0, '2' }, /* synonym */
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{ "tcp-flags", 1, 0, '4' },
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{ "tcp-option", 1, 0, '5' },
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parse_tcp_ports(const char *portstring, u_int16_t *ports)
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buffer = strdup(portstring);
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if ((cp = strchr(buffer, ':')) == NULL)
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ports[0] = ports[1] = parse_port(buffer, "tcp");
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ports[0] = buffer[0] ? parse_port(buffer, "tcp") : 0;
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ports[1] = cp[0] ? parse_port(cp, "tcp") : 0xFFFF;
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if (ports[0] > ports[1])
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exit_error(PARAMETER_PROBLEM,
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"invalid portrange (min > max)");
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struct tcp_flag_names {
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static struct tcp_flag_names tcp_flag_names[]
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parse_tcp_flag(const char *flags)
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buffer = strdup(flags);
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for (ptr = strtok(buffer, ","); ptr; ptr = strtok(NULL, ",")) {
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i < sizeof(tcp_flag_names)/sizeof(struct tcp_flag_names);
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if (strcasecmp(tcp_flag_names[i].name, ptr) == 0) {
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ret |= tcp_flag_names[i].flag;
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if (i == sizeof(tcp_flag_names)/sizeof(struct tcp_flag_names))
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exit_error(PARAMETER_PROBLEM,
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"Unknown TCP flag `%s'", ptr);
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parse_tcp_flags(struct ipt_tcp *tcpinfo,
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tcpinfo->flg_mask = parse_tcp_flag(mask);
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tcpinfo->flg_cmp = parse_tcp_flag(cmp);
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tcpinfo->invflags |= IPT_TCP_INV_FLAGS;
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parse_tcp_option(const char *option, u_int8_t *result)
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if (string_to_number(option, 1, 255, &ret) == -1)
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exit_error(PARAMETER_PROBLEM, "Bad TCP option `%s'", option);
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*result = (u_int8_t)ret;
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/* Initialize the match. */
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init(struct ipt_entry_match *m, unsigned int *nfcache)
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struct ipt_tcp *tcpinfo = (struct ipt_tcp *)m->data;
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tcpinfo->spts[1] = tcpinfo->dpts[1] = 0xFFFF;
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#define TCP_SRC_PORTS 0x01
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#define TCP_DST_PORTS 0x02
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#define TCP_FLAGS 0x04
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#define TCP_OPTION 0x08
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/* Function which parses command options; returns true if it
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parse(int c, char **argv, int invert, unsigned int *flags,
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const struct ipt_entry *entry,
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unsigned int *nfcache,
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struct ipt_entry_match **match)
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struct ipt_tcp *tcpinfo = (struct ipt_tcp *)(*match)->data;
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if (*flags & TCP_SRC_PORTS)
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exit_error(PARAMETER_PROBLEM,
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"Only one `--source-port' allowed");
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check_inverse(optarg, &invert, &optind, 0);
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parse_tcp_ports(argv[optind-1], tcpinfo->spts);
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tcpinfo->invflags |= IPT_TCP_INV_SRCPT;
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*flags |= TCP_SRC_PORTS;
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if (*flags & TCP_DST_PORTS)
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exit_error(PARAMETER_PROBLEM,
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"Only one `--destination-port' allowed");
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check_inverse(optarg, &invert, &optind, 0);
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parse_tcp_ports(argv[optind-1], tcpinfo->dpts);
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tcpinfo->invflags |= IPT_TCP_INV_DSTPT;
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*flags |= TCP_DST_PORTS;
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if (*flags & TCP_FLAGS)
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exit_error(PARAMETER_PROBLEM,
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"Only one of `--syn' or `--tcp-flags' "
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parse_tcp_flags(tcpinfo, "SYN,RST,ACK,FIN", "SYN", invert);
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if (*flags & TCP_FLAGS)
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exit_error(PARAMETER_PROBLEM,
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"Only one of `--syn' or `--tcp-flags' "
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check_inverse(optarg, &invert, &optind, 0);
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|| argv[optind][0] == '-' || argv[optind][0] == '!')
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exit_error(PARAMETER_PROBLEM,
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"--tcp-flags requires two args.");
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parse_tcp_flags(tcpinfo, argv[optind-1], argv[optind],
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if (*flags & TCP_OPTION)
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exit_error(PARAMETER_PROBLEM,
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"Only one `--tcp-option' allowed");
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check_inverse(optarg, &invert, &optind, 0);
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parse_tcp_option(argv[optind-1], &tcpinfo->option);
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tcpinfo->invflags |= IPT_TCP_INV_OPTION;
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*flags |= TCP_OPTION;
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/* Final check; we don't care. */
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final_check(unsigned int flags)
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port_to_service(int port)
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struct servent *service;
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if ((service = getservbyport(htons(port), "tcp")))
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return service->s_name;
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print_port(u_int16_t port, int numeric)
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if (numeric || (service = port_to_service(port)) == NULL)
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printf("%s", service);
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print_ports(const char *name, u_int16_t min, u_int16_t max,
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int invert, int numeric)
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const char *inv = invert ? "!" : "";
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if (min != 0 || max != 0xFFFF || invert) {
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print_port(min, numeric);
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print_port(min, numeric);
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print_port(max, numeric);
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print_option(u_int8_t option, int invert, int numeric)
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if (option || invert)
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printf("option=%s%u ", invert ? "!" : "", option);
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print_tcpf(u_int8_t flags)
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for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);
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printf("%s", tcp_flag_names[i].name);
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flags &= ~tcp_flag_names[i].flag;
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print_flags(u_int8_t mask, u_int8_t cmp, int invert, int numeric)
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if (mask || invert) {
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printf("flags:%s", invert ? "!" : "");
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printf("0x%02X/0x%02X ", mask, cmp);
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/* Prints out the union ipt_matchinfo. */
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print(const struct ipt_ip *ip,
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const struct ipt_entry_match *match, int numeric)
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const struct ipt_tcp *tcp = (struct ipt_tcp *)match->data;
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print_ports("spt", tcp->spts[0], tcp->spts[1],
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tcp->invflags & IPT_TCP_INV_SRCPT,
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print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
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tcp->invflags & IPT_TCP_INV_DSTPT,
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print_option(tcp->option,
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tcp->invflags & IPT_TCP_INV_OPTION,
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print_flags(tcp->flg_mask, tcp->flg_cmp,
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tcp->invflags & IPT_TCP_INV_FLAGS,
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if (tcp->invflags & ~IPT_TCP_INV_MASK)
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printf("Unknown invflags: 0x%X ",
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tcp->invflags & ~IPT_TCP_INV_MASK);
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/* Saves the union ipt_matchinfo in parsable form to stdout. */
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static void save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
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const struct ipt_tcp *tcpinfo = (struct ipt_tcp *)match->data;
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if (tcpinfo->spts[0] != 0
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|| tcpinfo->spts[1] != 0xFFFF) {
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if (tcpinfo->invflags & IPT_TCP_INV_SRCPT)
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printf("--sport %u:%u ",
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printf("--sport %u ",
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if (tcpinfo->dpts[0] != 0
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|| tcpinfo->dpts[1] != 0xFFFF) {
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if (tcpinfo->invflags & IPT_TCP_INV_DSTPT)
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printf("--dport %u:%u ",
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printf("--dport %u ",
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|| (tcpinfo->invflags & IPT_TCP_INV_OPTION)) {
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if (tcpinfo->invflags & IPT_TCP_INV_OPTION)
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printf("--tcp-option %u ", tcpinfo->option);
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if (tcpinfo->flg_mask
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|| (tcpinfo->invflags & IPT_TCP_INV_FLAGS)) {
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if (tcpinfo->invflags & IPT_TCP_INV_FLAGS)
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printf("--tcp-flags ");
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if (tcpinfo->flg_mask != 0xFF) {
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print_tcpf(tcpinfo->flg_mask);
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print_tcpf(tcpinfo->flg_cmp);
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static struct iptables_match tcp = {
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.version = IPTABLES_VERSION,
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.size = IPT_ALIGN(sizeof(struct ipt_tcp)),
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.userspacesize = IPT_ALIGN(sizeof(struct ipt_tcp)),
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.final_check = &final_check,
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register_match(&tcp);