1 /* Shared library add-on to iptables to add string matching support.
2 *
3 * Copyright (C) 2000 Emmanuel Roger <winfield@freegates.be>
4 *
5 * 2005-08-05 Pablo Neira Ayuso <pablo@eurodev.net>
6 * - reimplemented to use new string matching iptables match
7 * - add functionality to match packets by using window offsets
8 * - add functionality to select the string matching algorithm
9 *
10 * ChangeLog
11 * 29.12.2003: Michael Rash <mbr@cipherdyne.org>
12 * Fixed iptables save/restore for ascii strings
13 * that contain space chars, and hex strings that
14 * contain embedded NULL chars. Updated to print
15 * strings in hex mode if any non-printable char
16 * is contained within the string.
17 *
18 * 27.01.2001: Gianni Tedesco <gianni@ecsc.co.uk>
19 * Changed --tos to --string in save(). Also
20 * updated to work with slightly modified
21 * ipt_string_info.
22 */
23 #include <stdio.h>
24 #include <string.h>
25 #include <stdlib.h>
26 #include <ctype.h>
27 #include <xtables.h>
28 #include <linux/netfilter/xt_string.h>
29
30 enum {
31 O_FROM = 0,
32 O_TO,
33 O_ALGO,
34 O_ICASE,
35 O_STRING,
36 O_HEX_STRING,
37 F_STRING = 1 << O_STRING,
38 F_HEX_STRING = 1 << O_HEX_STRING,
39 F_OP_ANY = F_STRING | F_HEX_STRING,
40 };
41
string_help(void)42 static void string_help(void)
43 {
44 printf(
45 "string match options:\n"
46 "--from Offset to start searching from\n"
47 "--to Offset to stop searching\n"
48 "--algo Algorithm\n"
49 "--icase Ignore case (default: 0)\n"
50 "[!] --string string Match a string in a packet\n"
51 "[!] --hex-string string Match a hex string in a packet\n");
52 }
53
54 #define s struct xt_string_info
55 static const struct xt_option_entry string_opts[] = {
56 {.name = "from", .id = O_FROM, .type = XTTYPE_UINT16,
57 .flags = XTOPT_PUT, XTOPT_POINTER(s, from_offset)},
58 {.name = "to", .id = O_TO, .type = XTTYPE_UINT16,
59 .flags = XTOPT_PUT, XTOPT_POINTER(s, to_offset)},
60 {.name = "algo", .id = O_ALGO, .type = XTTYPE_STRING,
61 .flags = XTOPT_MAND | XTOPT_PUT, XTOPT_POINTER(s, algo)},
62 {.name = "string", .id = O_STRING, .type = XTTYPE_STRING,
63 .flags = XTOPT_INVERT, .excl = F_HEX_STRING},
64 {.name = "hex-string", .id = O_HEX_STRING, .type = XTTYPE_STRING,
65 .flags = XTOPT_INVERT, .excl = F_STRING},
66 {.name = "icase", .id = O_ICASE, .type = XTTYPE_NONE},
67 XTOPT_TABLEEND,
68 };
69 #undef s
70
string_init(struct xt_entry_match * m)71 static void string_init(struct xt_entry_match *m)
72 {
73 struct xt_string_info *i = (struct xt_string_info *) m->data;
74
75 i->to_offset = UINT16_MAX;
76 }
77
78 static void
parse_string(const char * s,struct xt_string_info * info)79 parse_string(const char *s, struct xt_string_info *info)
80 {
81 /* xt_string does not need \0 at the end of the pattern */
82 if (strlen(s) <= XT_STRING_MAX_PATTERN_SIZE) {
83 strncpy(info->pattern, s, XT_STRING_MAX_PATTERN_SIZE);
84 info->patlen = strnlen(s, XT_STRING_MAX_PATTERN_SIZE);
85 return;
86 }
87 xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
88 }
89
90 static void
parse_hex_string(const char * s,struct xt_string_info * info)91 parse_hex_string(const char *s, struct xt_string_info *info)
92 {
93 int i=0, slen, sindex=0, schar;
94 short hex_f = 0, literal_f = 0;
95 char hextmp[3];
96
97 slen = strlen(s);
98
99 if (slen == 0) {
100 xtables_error(PARAMETER_PROBLEM,
101 "STRING must contain at least one char");
102 }
103
104 while (i < slen) {
105 if (s[i] == '\\' && !hex_f) {
106 literal_f = 1;
107 } else if (s[i] == '\\') {
108 xtables_error(PARAMETER_PROBLEM,
109 "Cannot include literals in hex data");
110 } else if (s[i] == '|') {
111 if (hex_f)
112 hex_f = 0;
113 else {
114 hex_f = 1;
115 /* get past any initial whitespace just after the '|' */
116 while (s[i+1] == ' ')
117 i++;
118 }
119 if (i+1 >= slen)
120 break;
121 else
122 i++; /* advance to the next character */
123 }
124
125 if (literal_f) {
126 if (i+1 >= slen) {
127 xtables_error(PARAMETER_PROBLEM,
128 "Bad literal placement at end of string");
129 }
130 info->pattern[sindex] = s[i+1];
131 i += 2; /* skip over literal char */
132 literal_f = 0;
133 } else if (hex_f) {
134 if (i+1 >= slen) {
135 xtables_error(PARAMETER_PROBLEM,
136 "Odd number of hex digits");
137 }
138 if (i+2 >= slen) {
139 /* must end with a "|" */
140 xtables_error(PARAMETER_PROBLEM, "Invalid hex block");
141 }
142 if (! isxdigit(s[i])) /* check for valid hex char */
143 xtables_error(PARAMETER_PROBLEM, "Invalid hex char '%c'", s[i]);
144 if (! isxdigit(s[i+1])) /* check for valid hex char */
145 xtables_error(PARAMETER_PROBLEM, "Invalid hex char '%c'", s[i+1]);
146 hextmp[0] = s[i];
147 hextmp[1] = s[i+1];
148 hextmp[2] = '\0';
149 if (! sscanf(hextmp, "%x", &schar))
150 xtables_error(PARAMETER_PROBLEM,
151 "Invalid hex char `%c'", s[i]);
152 info->pattern[sindex] = (char) schar;
153 if (s[i+2] == ' ')
154 i += 3; /* spaces included in the hex block */
155 else
156 i += 2;
157 } else { /* the char is not part of hex data, so just copy */
158 info->pattern[sindex] = s[i];
159 i++;
160 }
161 if (sindex > XT_STRING_MAX_PATTERN_SIZE)
162 xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
163 sindex++;
164 }
165 info->patlen = sindex;
166 }
167
string_parse(struct xt_option_call * cb)168 static void string_parse(struct xt_option_call *cb)
169 {
170 struct xt_string_info *stringinfo = cb->data;
171 const unsigned int revision = (*cb->match)->u.user.revision;
172
173 xtables_option_parse(cb);
174 switch (cb->entry->id) {
175 case O_STRING:
176 parse_string(cb->arg, stringinfo);
177 if (cb->invert) {
178 if (revision == 0)
179 stringinfo->u.v0.invert = 1;
180 else
181 stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
182 }
183 break;
184 case O_HEX_STRING:
185 parse_hex_string(cb->arg, stringinfo); /* sets length */
186 if (cb->invert) {
187 if (revision == 0)
188 stringinfo->u.v0.invert = 1;
189 else
190 stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
191 }
192 break;
193 case O_ICASE:
194 if (revision == 0)
195 xtables_error(VERSION_PROBLEM,
196 "Kernel doesn't support --icase");
197
198 stringinfo->u.v1.flags |= XT_STRING_FLAG_IGNORECASE;
199 break;
200 }
201 }
202
string_check(struct xt_fcheck_call * cb)203 static void string_check(struct xt_fcheck_call *cb)
204 {
205 if (!(cb->xflags & F_OP_ANY))
206 xtables_error(PARAMETER_PROBLEM,
207 "STRING match: You must specify `--string' or "
208 "`--hex-string'");
209 }
210
211 /* Test to see if the string contains non-printable chars or quotes */
212 static unsigned short int
is_hex_string(const char * str,const unsigned short int len)213 is_hex_string(const char *str, const unsigned short int len)
214 {
215 unsigned int i;
216 for (i=0; i < len; i++)
217 if (! isprint(str[i]))
218 return 1; /* string contains at least one non-printable char */
219 /* use hex output if the last char is a "\" */
220 if ((unsigned char) str[len-1] == 0x5c)
221 return 1;
222 return 0;
223 }
224
225 /* Print string with "|" chars included as one would pass to --hex-string */
226 static void
print_hex_string(const char * str,const unsigned short int len)227 print_hex_string(const char *str, const unsigned short int len)
228 {
229 unsigned int i;
230 /* start hex block */
231 printf("\"|");
232 for (i=0; i < len; i++) {
233 /* see if we need to prepend a zero */
234 if ((unsigned char) str[i] <= 0x0F)
235 printf("0%x", (unsigned char) str[i]);
236 else
237 printf("%x", (unsigned char) str[i]);
238 }
239 /* close hex block */
240 printf("|\" ");
241 }
242
243 static void
print_string(const char * str,const unsigned short int len)244 print_string(const char *str, const unsigned short int len)
245 {
246 unsigned int i;
247 printf(" \"");
248 for (i=0; i < len; i++) {
249 if ((unsigned char) str[i] == 0x22) /* escape any embedded quotes */
250 printf("%c", 0x5c);
251 printf("%c", (unsigned char) str[i]);
252 }
253 printf("\""); /* closing quote */
254 }
255
256 static void
string_print(const void * ip,const struct xt_entry_match * match,int numeric)257 string_print(const void *ip, const struct xt_entry_match *match, int numeric)
258 {
259 const struct xt_string_info *info =
260 (const struct xt_string_info*) match->data;
261 const int revision = match->u.user.revision;
262 int invert = (revision == 0 ? info->u.v0.invert :
263 info->u.v1.flags & XT_STRING_FLAG_INVERT);
264
265 if (is_hex_string(info->pattern, info->patlen)) {
266 printf(" STRING match %s", invert ? "!" : "");
267 print_hex_string(info->pattern, info->patlen);
268 } else {
269 printf(" STRING match %s", invert ? "!" : "");
270 print_string(info->pattern, info->patlen);
271 }
272 printf(" ALGO name %s", info->algo);
273 if (info->from_offset != 0)
274 printf(" FROM %u", info->from_offset);
275 if (info->to_offset != 0)
276 printf(" TO %u", info->to_offset);
277 if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
278 printf(" ICASE");
279 }
280
string_save(const void * ip,const struct xt_entry_match * match)281 static void string_save(const void *ip, const struct xt_entry_match *match)
282 {
283 const struct xt_string_info *info =
284 (const struct xt_string_info*) match->data;
285 const int revision = match->u.user.revision;
286 int invert = (revision == 0 ? info->u.v0.invert :
287 info->u.v1.flags & XT_STRING_FLAG_INVERT);
288
289 if (is_hex_string(info->pattern, info->patlen)) {
290 printf("%s --hex-string", (invert) ? " !" : "");
291 print_hex_string(info->pattern, info->patlen);
292 } else {
293 printf("%s --string", (invert) ? " !": "");
294 print_string(info->pattern, info->patlen);
295 }
296 printf(" --algo %s", info->algo);
297 if (info->from_offset != 0)
298 printf(" --from %u", info->from_offset);
299 if (info->to_offset != 0)
300 printf(" --to %u", info->to_offset);
301 if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
302 printf(" --icase");
303 }
304
305
306 static struct xtables_match string_mt_reg[] = {
307 {
308 .name = "string",
309 .revision = 0,
310 .family = NFPROTO_UNSPEC,
311 .version = XTABLES_VERSION,
312 .size = XT_ALIGN(sizeof(struct xt_string_info)),
313 .userspacesize = offsetof(struct xt_string_info, config),
314 .help = string_help,
315 .init = string_init,
316 .print = string_print,
317 .save = string_save,
318 .x6_parse = string_parse,
319 .x6_fcheck = string_check,
320 .x6_options = string_opts,
321 },
322 {
323 .name = "string",
324 .revision = 1,
325 .family = NFPROTO_UNSPEC,
326 .version = XTABLES_VERSION,
327 .size = XT_ALIGN(sizeof(struct xt_string_info)),
328 .userspacesize = offsetof(struct xt_string_info, config),
329 .help = string_help,
330 .init = string_init,
331 .print = string_print,
332 .save = string_save,
333 .x6_parse = string_parse,
334 .x6_fcheck = string_check,
335 .x6_options = string_opts,
336 },
337 };
338
_init(void)339 void _init(void)
340 {
341 xtables_register_matches(string_mt_reg, ARRAY_SIZE(string_mt_reg));
342 }
343