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-rw-r--r--extensions/libxt_string.c389
1 files changed, 389 insertions, 0 deletions
diff --git a/extensions/libxt_string.c b/extensions/libxt_string.c
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--- /dev/null
+++ b/extensions/libxt_string.c
@@ -0,0 +1,389 @@
+/* Shared library add-on to iptables to add string matching support.
+ *
+ * Copyright (C) 2000 Emmanuel Roger <winfield@freegates.be>
+ *
+ * 2005-08-05 Pablo Neira Ayuso <pablo@eurodev.net>
+ * - reimplemented to use new string matching iptables match
+ * - add functionality to match packets by using window offsets
+ * - add functionality to select the string matching algorithm
+ *
+ * ChangeLog
+ * 29.12.2003: Michael Rash <mbr@cipherdyne.org>
+ * Fixed iptables save/restore for ascii strings
+ * that contain space chars, and hex strings that
+ * contain embedded NULL chars. Updated to print
+ * strings in hex mode if any non-printable char
+ * is contained within the string.
+ *
+ * 27.01.2001: Gianni Tedesco <gianni@ecsc.co.uk>
+ * Changed --tos to --string in save(). Also
+ * updated to work with slightly modified
+ * ipt_string_info.
+ */
+#define _GNU_SOURCE 1
+#include <stdio.h>
+#include <netdb.h>
+#include <string.h>
+#include <stdlib.h>
+#include <getopt.h>
+#include <ctype.h>
+#include <xtables.h>
+#include <stddef.h>
+#include <linux/netfilter/xt_string.h>
+
+static void string_help(void)
+{
+ printf(
+"string match options:\n"
+"--from Offset to start searching from\n"
+"--to Offset to stop searching\n"
+"--algo Algorithm\n"
+"--icase Ignore case (default: 0)\n"
+"[!] --string string Match a string in a packet\n"
+"[!] --hex-string string Match a hex string in a packet\n");
+}
+
+static const struct option string_opts[] = {
+ { "from", 1, NULL, '1' },
+ { "to", 1, NULL, '2' },
+ { "algo", 1, NULL, '3' },
+ { "string", 1, NULL, '4' },
+ { "hex-string", 1, NULL, '5' },
+ { "icase", 0, NULL, '6' },
+ { .name = NULL }
+};
+
+static void string_init(struct xt_entry_match *m)
+{
+ struct xt_string_info *i = (struct xt_string_info *) m->data;
+
+ if (i->to_offset == 0)
+ i->to_offset = UINT16_MAX;
+}
+
+static void
+parse_string(const char *s, struct xt_string_info *info)
+{
+ /* xt_string does not need \0 at the end of the pattern */
+ if (strlen(s) <= XT_STRING_MAX_PATTERN_SIZE) {
+ strncpy(info->pattern, s, XT_STRING_MAX_PATTERN_SIZE);
+ info->patlen = strnlen(s, XT_STRING_MAX_PATTERN_SIZE);
+ return;
+ }
+ xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
+}
+
+static void
+parse_algo(const char *s, struct xt_string_info *info)
+{
+ /* xt_string needs \0 for algo name */
+ if (strlen(s) < XT_STRING_MAX_ALGO_NAME_SIZE) {
+ strncpy(info->algo, s, XT_STRING_MAX_ALGO_NAME_SIZE);
+ return;
+ }
+ xtables_error(PARAMETER_PROBLEM, "ALGO too long \"%s\"", s);
+}
+
+static void
+parse_hex_string(const char *s, struct xt_string_info *info)
+{
+ int i=0, slen, sindex=0, schar;
+ short hex_f = 0, literal_f = 0;
+ char hextmp[3];
+
+ slen = strlen(s);
+
+ if (slen == 0) {
+ xtables_error(PARAMETER_PROBLEM,
+ "STRING must contain at least one char");
+ }
+
+ while (i < slen) {
+ if (s[i] == '\\' && !hex_f) {
+ literal_f = 1;
+ } else if (s[i] == '\\') {
+ xtables_error(PARAMETER_PROBLEM,
+ "Cannot include literals in hex data");
+ } else if (s[i] == '|') {
+ if (hex_f)
+ hex_f = 0;
+ else {
+ hex_f = 1;
+ /* get past any initial whitespace just after the '|' */
+ while (s[i+1] == ' ')
+ i++;
+ }
+ if (i+1 >= slen)
+ break;
+ else
+ i++; /* advance to the next character */
+ }
+
+ if (literal_f) {
+ if (i+1 >= slen) {
+ xtables_error(PARAMETER_PROBLEM,
+ "Bad literal placement at end of string");
+ }
+ info->pattern[sindex] = s[i+1];
+ i += 2; /* skip over literal char */
+ literal_f = 0;
+ } else if (hex_f) {
+ if (i+1 >= slen) {
+ xtables_error(PARAMETER_PROBLEM,
+ "Odd number of hex digits");
+ }
+ if (i+2 >= slen) {
+ /* must end with a "|" */
+ xtables_error(PARAMETER_PROBLEM, "Invalid hex block");
+ }
+ if (! isxdigit(s[i])) /* check for valid hex char */
+ xtables_error(PARAMETER_PROBLEM, "Invalid hex char '%c'", s[i]);
+ if (! isxdigit(s[i+1])) /* check for valid hex char */
+ xtables_error(PARAMETER_PROBLEM, "Invalid hex char '%c'", s[i+1]);
+ hextmp[0] = s[i];
+ hextmp[1] = s[i+1];
+ hextmp[2] = '\0';
+ if (! sscanf(hextmp, "%x", &schar))
+ xtables_error(PARAMETER_PROBLEM,
+ "Invalid hex char `%c'", s[i]);
+ info->pattern[sindex] = (char) schar;
+ if (s[i+2] == ' ')
+ i += 3; /* spaces included in the hex block */
+ else
+ i += 2;
+ } else { /* the char is not part of hex data, so just copy */
+ info->pattern[sindex] = s[i];
+ i++;
+ }
+ if (sindex > XT_STRING_MAX_PATTERN_SIZE)
+ xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
+ sindex++;
+ }
+ info->patlen = sindex;
+}
+
+#define STRING 0x1
+#define ALGO 0x2
+#define FROM 0x4
+#define TO 0x8
+#define ICASE 0x10
+
+static int
+string_parse(int c, char **argv, int invert, unsigned int *flags,
+ const void *entry, struct xt_entry_match **match)
+{
+ struct xt_string_info *stringinfo =
+ (struct xt_string_info *)(*match)->data;
+ const int revision = (*match)->u.user.revision;
+
+ switch (c) {
+ case '1':
+ if (*flags & FROM)
+ xtables_error(PARAMETER_PROBLEM,
+ "Can't specify multiple --from");
+ stringinfo->from_offset = atoi(optarg);
+ *flags |= FROM;
+ break;
+ case '2':
+ if (*flags & TO)
+ xtables_error(PARAMETER_PROBLEM,
+ "Can't specify multiple --to");
+ stringinfo->to_offset = atoi(optarg);
+ *flags |= TO;
+ break;
+ case '3':
+ if (*flags & ALGO)
+ xtables_error(PARAMETER_PROBLEM,
+ "Can't specify multiple --algo");
+ parse_algo(optarg, stringinfo);
+ *flags |= ALGO;
+ break;
+ case '4':
+ if (*flags & STRING)
+ xtables_error(PARAMETER_PROBLEM,
+ "Can't specify multiple --string");
+ xtables_check_inverse(optarg, &invert, &optind, 0, argv);
+ parse_string(optarg, stringinfo);
+ if (invert) {
+ if (revision == 0)
+ stringinfo->u.v0.invert = 1;
+ else
+ stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
+ }
+ *flags |= STRING;
+ break;
+
+ case '5':
+ if (*flags & STRING)
+ xtables_error(PARAMETER_PROBLEM,
+ "Can't specify multiple --hex-string");
+
+ xtables_check_inverse(optarg, &invert, &optind, 0, argv);
+ parse_hex_string(optarg, stringinfo); /* sets length */
+ if (invert) {
+ if (revision == 0)
+ stringinfo->u.v0.invert = 1;
+ else
+ stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
+ }
+ *flags |= STRING;
+ break;
+
+ case '6':
+ if (revision == 0)
+ xtables_error(VERSION_PROBLEM,
+ "Kernel doesn't support --icase");
+
+ stringinfo->u.v1.flags |= XT_STRING_FLAG_IGNORECASE;
+ *flags |= ICASE;
+ break;
+
+ default:
+ return 0;
+ }
+ return 1;
+}
+
+static void string_check(unsigned int flags)
+{
+ if (!(flags & STRING))
+ xtables_error(PARAMETER_PROBLEM,
+ "STRING match: You must specify `--string' or "
+ "`--hex-string'");
+ if (!(flags & ALGO))
+ xtables_error(PARAMETER_PROBLEM,
+ "STRING match: You must specify `--algo'");
+}
+
+/* Test to see if the string contains non-printable chars or quotes */
+static unsigned short int
+is_hex_string(const char *str, const unsigned short int len)
+{
+ unsigned int i;
+ for (i=0; i < len; i++)
+ if (! isprint(str[i]))
+ return 1; /* string contains at least one non-printable char */
+ /* use hex output if the last char is a "\" */
+ if ((unsigned char) str[len-1] == 0x5c)
+ return 1;
+ return 0;
+}
+
+/* Print string with "|" chars included as one would pass to --hex-string */
+static void
+print_hex_string(const char *str, const unsigned short int len)
+{
+ unsigned int i;
+ /* start hex block */
+ printf("\"|");
+ for (i=0; i < len; i++) {
+ /* see if we need to prepend a zero */
+ if ((unsigned char) str[i] <= 0x0F)
+ printf("0%x", (unsigned char) str[i]);
+ else
+ printf("%x", (unsigned char) str[i]);
+ }
+ /* close hex block */
+ printf("|\" ");
+}
+
+static void
+print_string(const char *str, const unsigned short int len)
+{
+ unsigned int i;
+ printf("\"");
+ for (i=0; i < len; i++) {
+ if ((unsigned char) str[i] == 0x22) /* escape any embedded quotes */
+ printf("%c", 0x5c);
+ printf("%c", (unsigned char) str[i]);
+ }
+ printf("\" "); /* closing space and quote */
+}
+
+static void
+string_print(const void *ip, const struct xt_entry_match *match, int numeric)
+{
+ const struct xt_string_info *info =
+ (const struct xt_string_info*) match->data;
+ const int revision = match->u.user.revision;
+ int invert = (revision == 0 ? info->u.v0.invert :
+ info->u.v1.flags & XT_STRING_FLAG_INVERT);
+
+ if (is_hex_string(info->pattern, info->patlen)) {
+ printf("STRING match %s", invert ? "!" : "");
+ print_hex_string(info->pattern, info->patlen);
+ } else {
+ printf("STRING match %s", invert ? "!" : "");
+ print_string(info->pattern, info->patlen);
+ }
+ printf("ALGO name %s ", info->algo);
+ if (info->from_offset != 0)
+ printf("FROM %u ", info->from_offset);
+ if (info->to_offset != 0)
+ printf("TO %u ", info->to_offset);
+ if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
+ printf("ICASE ");
+}
+
+static void string_save(const void *ip, const struct xt_entry_match *match)
+{
+ const struct xt_string_info *info =
+ (const struct xt_string_info*) match->data;
+ const int revision = match->u.user.revision;
+ int invert = (revision == 0 ? info->u.v0.invert :
+ info->u.v1.flags & XT_STRING_FLAG_INVERT);
+
+ if (is_hex_string(info->pattern, info->patlen)) {
+ printf("%s--hex-string ", (invert) ? "! ": "");
+ print_hex_string(info->pattern, info->patlen);
+ } else {
+ printf("%s--string ", (invert) ? "! ": "");
+ print_string(info->pattern, info->patlen);
+ }
+ printf("--algo %s ", info->algo);
+ if (info->from_offset != 0)
+ printf("--from %u ", info->from_offset);
+ if (info->to_offset != 0)
+ printf("--to %u ", info->to_offset);
+ if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
+ printf("--icase ");
+}
+
+
+static struct xtables_match string_mt_reg[] = {
+ {
+ .name = "string",
+ .revision = 0,
+ .family = NFPROTO_UNSPEC,
+ .version = XTABLES_VERSION,
+ .size = XT_ALIGN(sizeof(struct xt_string_info)),
+ .userspacesize = offsetof(struct xt_string_info, config),
+ .help = string_help,
+ .init = string_init,
+ .parse = string_parse,
+ .final_check = string_check,
+ .print = string_print,
+ .save = string_save,
+ .extra_opts = string_opts,
+ },
+ {
+ .name = "string",
+ .revision = 1,
+ .family = NFPROTO_UNSPEC,
+ .version = XTABLES_VERSION,
+ .size = XT_ALIGN(sizeof(struct xt_string_info)),
+ .userspacesize = offsetof(struct xt_string_info, config),
+ .help = string_help,
+ .init = string_init,
+ .parse = string_parse,
+ .final_check = string_check,
+ .print = string_print,
+ .save = string_save,
+ .extra_opts = string_opts,
+ },
+};
+
+void _init(void)
+{
+ xtables_register_matches(string_mt_reg, ARRAY_SIZE(string_mt_reg));
+}
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