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340 lines
9.6 KiB
340 lines
9.6 KiB
/* Shared library add-on to iptables to add string matching support.
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*
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* Copyright (C) 2000 Emmanuel Roger <winfield@freegates.be>
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*
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* 2005-08-05 Pablo Neira Ayuso <pablo@eurodev.net>
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* - reimplemented to use new string matching iptables match
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* - add functionality to match packets by using window offsets
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* - add functionality to select the string matching algorithm
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*
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* ChangeLog
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* 29.12.2003: Michael Rash <mbr@cipherdyne.org>
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* Fixed iptables save/restore for ascii strings
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* that contain space chars, and hex strings that
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* contain embedded NULL chars. Updated to print
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* strings in hex mode if any non-printable char
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* is contained within the string.
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*
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* 27.01.2001: Gianni Tedesco <gianni@ecsc.co.uk>
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* Changed --tos to --string in save(). Also
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* updated to work with slightly modified
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* ipt_string_info.
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*/
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#define _GNU_SOURCE 1 /* strnlen for older glibcs */
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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#include <ctype.h>
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#include <xtables.h>
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#include <linux/netfilter/xt_string.h>
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enum {
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O_FROM = 0,
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O_TO,
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O_ALGO,
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O_ICASE,
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O_STRING,
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O_HEX_STRING,
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F_STRING = 1 << O_STRING,
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F_HEX_STRING = 1 << O_HEX_STRING,
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F_OP_ANY = F_STRING | F_HEX_STRING,
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};
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static void string_help(void)
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{
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printf(
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"string match options:\n"
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"--from Offset to start searching from\n"
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"--to Offset to stop searching\n"
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"--algo Algorithm\n"
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"--icase Ignore case (default: 0)\n"
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"[!] --string string Match a string in a packet\n"
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"[!] --hex-string string Match a hex string in a packet\n");
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}
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#define s struct xt_string_info
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static const struct xt_option_entry string_opts[] = {
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{.name = "from", .id = O_FROM, .type = XTTYPE_UINT16,
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.flags = XTOPT_PUT, XTOPT_POINTER(s, from_offset)},
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{.name = "to", .id = O_TO, .type = XTTYPE_UINT16,
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.flags = XTOPT_PUT, XTOPT_POINTER(s, to_offset)},
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{.name = "algo", .id = O_ALGO, .type = XTTYPE_STRING,
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.flags = XTOPT_MAND | XTOPT_PUT, XTOPT_POINTER(s, algo)},
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{.name = "string", .id = O_STRING, .type = XTTYPE_STRING,
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.flags = XTOPT_INVERT, .excl = F_HEX_STRING},
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{.name = "hex-string", .id = O_HEX_STRING, .type = XTTYPE_STRING,
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.flags = XTOPT_INVERT, .excl = F_STRING},
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{.name = "icase", .id = O_ICASE, .type = XTTYPE_NONE},
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XTOPT_TABLEEND,
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};
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#undef s
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static void string_init(struct xt_entry_match *m)
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{
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struct xt_string_info *i = (struct xt_string_info *) m->data;
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i->to_offset = UINT16_MAX;
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}
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static void
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parse_string(const char *s, struct xt_string_info *info)
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{
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/* xt_string does not need \0 at the end of the pattern */
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if (strlen(s) <= XT_STRING_MAX_PATTERN_SIZE) {
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strncpy(info->pattern, s, XT_STRING_MAX_PATTERN_SIZE);
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info->patlen = strnlen(s, XT_STRING_MAX_PATTERN_SIZE);
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return;
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}
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xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
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}
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static void
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parse_hex_string(const char *s, struct xt_string_info *info)
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{
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int i=0, slen, sindex=0, schar;
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short hex_f = 0, literal_f = 0;
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char hextmp[3];
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slen = strlen(s);
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if (slen == 0) {
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xtables_error(PARAMETER_PROBLEM,
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"STRING must contain at least one char");
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}
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while (i < slen) {
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if (sindex >= XT_STRING_MAX_PATTERN_SIZE)
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xtables_error(PARAMETER_PROBLEM,
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"STRING too long \"%s\"", s);
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if (s[i] == '\\' && !hex_f) {
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literal_f = 1;
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} else if (s[i] == '\\') {
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xtables_error(PARAMETER_PROBLEM,
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"Cannot include literals in hex data");
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} else if (s[i] == '|') {
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if (hex_f)
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hex_f = 0;
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else {
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hex_f = 1;
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/* get past any initial whitespace just after the '|' */
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while (s[i+1] == ' ')
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i++;
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}
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if (i+1 >= slen)
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break;
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else
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i++; /* advance to the next character */
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}
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if (literal_f) {
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if (i+1 >= slen) {
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xtables_error(PARAMETER_PROBLEM,
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"Bad literal placement at end of string");
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}
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info->pattern[sindex] = s[i+1];
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i += 2; /* skip over literal char */
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literal_f = 0;
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} else if (hex_f) {
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if (i+1 >= slen) {
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xtables_error(PARAMETER_PROBLEM,
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"Odd number of hex digits");
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}
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if (i+2 >= slen) {
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/* must end with a "|" */
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xtables_error(PARAMETER_PROBLEM, "Invalid hex block");
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}
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if (! isxdigit(s[i])) /* check for valid hex char */
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xtables_error(PARAMETER_PROBLEM, "Invalid hex char '%c'", s[i]);
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if (! isxdigit(s[i+1])) /* check for valid hex char */
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xtables_error(PARAMETER_PROBLEM, "Invalid hex char '%c'", s[i+1]);
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hextmp[0] = s[i];
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hextmp[1] = s[i+1];
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hextmp[2] = '\0';
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if (! sscanf(hextmp, "%x", &schar))
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xtables_error(PARAMETER_PROBLEM,
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"Invalid hex char `%c'", s[i]);
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info->pattern[sindex] = (char) schar;
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if (s[i+2] == ' ')
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i += 3; /* spaces included in the hex block */
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else
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i += 2;
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} else { /* the char is not part of hex data, so just copy */
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info->pattern[sindex] = s[i];
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i++;
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}
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sindex++;
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}
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info->patlen = sindex;
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}
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static void string_parse(struct xt_option_call *cb)
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{
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struct xt_string_info *stringinfo = cb->data;
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const unsigned int revision = (*cb->match)->u.user.revision;
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xtables_option_parse(cb);
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switch (cb->entry->id) {
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case O_STRING:
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parse_string(cb->arg, stringinfo);
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if (cb->invert) {
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if (revision == 0)
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stringinfo->u.v0.invert = 1;
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else
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stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
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}
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break;
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case O_HEX_STRING:
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parse_hex_string(cb->arg, stringinfo); /* sets length */
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if (cb->invert) {
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if (revision == 0)
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stringinfo->u.v0.invert = 1;
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else
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stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
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}
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break;
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case O_ICASE:
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if (revision == 0)
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xtables_error(VERSION_PROBLEM,
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"Kernel doesn't support --icase");
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stringinfo->u.v1.flags |= XT_STRING_FLAG_IGNORECASE;
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break;
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}
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}
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static void string_check(struct xt_fcheck_call *cb)
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{
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if (!(cb->xflags & F_OP_ANY))
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xtables_error(PARAMETER_PROBLEM,
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"STRING match: You must specify `--string' or "
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"`--hex-string'");
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}
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/* Test to see if the string contains non-printable chars or quotes */
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static unsigned short int
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is_hex_string(const char *str, const unsigned short int len)
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{
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unsigned int i;
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for (i=0; i < len; i++)
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if (! isprint(str[i]))
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return 1; /* string contains at least one non-printable char */
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/* use hex output if the last char is a "\" */
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if (str[len-1] == '\\')
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return 1;
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return 0;
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}
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/* Print string with "|" chars included as one would pass to --hex-string */
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static void
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print_hex_string(const char *str, const unsigned short int len)
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{
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unsigned int i;
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/* start hex block */
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printf(" \"|");
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for (i=0; i < len; i++)
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printf("%02x", (unsigned char)str[i]);
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/* close hex block */
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printf("|\"");
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}
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static void
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print_string(const char *str, const unsigned short int len)
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{
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unsigned int i;
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printf(" \"");
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for (i=0; i < len; i++) {
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if (str[i] == '\"' || str[i] == '\\')
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putchar('\\');
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printf("%c", (unsigned char) str[i]);
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}
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printf("\""); /* closing quote */
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}
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static void
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string_print(const void *ip, const struct xt_entry_match *match, int numeric)
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{
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const struct xt_string_info *info =
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(const struct xt_string_info*) match->data;
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const int revision = match->u.user.revision;
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int invert = (revision == 0 ? info->u.v0.invert :
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info->u.v1.flags & XT_STRING_FLAG_INVERT);
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if (is_hex_string(info->pattern, info->patlen)) {
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printf(" STRING match %s", invert ? "!" : "");
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print_hex_string(info->pattern, info->patlen);
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} else {
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printf(" STRING match %s", invert ? "!" : "");
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print_string(info->pattern, info->patlen);
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}
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printf(" ALGO name %s", info->algo);
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if (info->from_offset != 0)
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printf(" FROM %u", info->from_offset);
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if (info->to_offset != 0)
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printf(" TO %u", info->to_offset);
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if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
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printf(" ICASE");
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}
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static void string_save(const void *ip, const struct xt_entry_match *match)
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{
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const struct xt_string_info *info =
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(const struct xt_string_info*) match->data;
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const int revision = match->u.user.revision;
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int invert = (revision == 0 ? info->u.v0.invert :
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info->u.v1.flags & XT_STRING_FLAG_INVERT);
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if (is_hex_string(info->pattern, info->patlen)) {
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printf("%s --hex-string", (invert) ? " !" : "");
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print_hex_string(info->pattern, info->patlen);
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} else {
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printf("%s --string", (invert) ? " !": "");
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print_string(info->pattern, info->patlen);
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}
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printf(" --algo %s", info->algo);
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if (info->from_offset != 0)
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printf(" --from %u", info->from_offset);
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if (info->to_offset != 0)
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printf(" --to %u", info->to_offset);
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if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
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printf(" --icase");
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}
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static struct xtables_match string_mt_reg[] = {
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{
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.name = "string",
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.revision = 0,
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.family = NFPROTO_UNSPEC,
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.version = XTABLES_VERSION,
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.size = XT_ALIGN(sizeof(struct xt_string_info)),
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.userspacesize = offsetof(struct xt_string_info, config),
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.help = string_help,
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.init = string_init,
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.print = string_print,
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.save = string_save,
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.x6_parse = string_parse,
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.x6_fcheck = string_check,
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.x6_options = string_opts,
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},
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{
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.name = "string",
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.revision = 1,
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.family = NFPROTO_UNSPEC,
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.version = XTABLES_VERSION,
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.size = XT_ALIGN(sizeof(struct xt_string_info)),
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.userspacesize = offsetof(struct xt_string_info, config),
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.help = string_help,
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.init = string_init,
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.print = string_print,
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.save = string_save,
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.x6_parse = string_parse,
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.x6_fcheck = string_check,
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.x6_options = string_opts,
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},
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};
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void _init(void)
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{
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xtables_register_matches(string_mt_reg, ARRAY_SIZE(string_mt_reg));
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}
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