release/src/router/iptables/extensions/libipt_string.c

   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 <netdb.h>
  25 #include <string.h>
  26 #include <stdlib.h>
  27 #include <getopt.h>
  28 #include <ctype.h>
  29 #include <iptables.h>
  30 #include <stddef.h>
  31 #include <linux/netfilter_ipv4/ipt_string.h>
  32
  33 /* Function which prints out usage message. */
  34 static void
  35 help(void)
  36 {
  37         printf(
  38 "STRING match v%s options:\n"
  39 "--from                       Offset to start searching from\n"
  40 "--to                         Offset to stop searching\n"
  41 "--algo                       Algorithm\n"
  42 "--string [!] string          Match a string in a packet\n"
  43 "--hex-string [!] string      Match a hex string in a packet\n",
  44 IPTABLES_VERSION);
  45 }
  46
  47 static struct option opts[] = {
  48         { "from", 1, 0, '1' },
  49         { "to", 1, 0, '2' },
  50         { "algo", 1, 0, '3' },
  51         { "string", 1, 0, '4' },
  52         { "hex-string", 1, 0, '5' },
  53         {0}
  54 };
  55
  56 static void
  57 init(struct ipt_entry_match *m, unsigned int *nfcache)
  58 {
  59         struct ipt_string_info *i = (struct ipt_string_info *) m->data;
  60
  61         if (i->to_offset == 0)
  62                 i->to_offset = (u_int16_t) ~0UL;
  63 }
  64
  65 static void
  66 parse_string(const char *s, struct ipt_string_info *info)
  67 {
  68         if (strlen(s) <= IPT_STRING_MAX_PATTERN_SIZE) {
  69                 strncpy(info->pattern, s, IPT_STRING_MAX_PATTERN_SIZE);
  70                 info->patlen = strlen(s);
  71                 return;
  72         }
  73         exit_error(PARAMETER_PROBLEM, "STRING too long `%s'", s);
  74 }
  75
  76 static void
  77 parse_algo(const char *s, struct ipt_string_info *info)
  78 {
  79         if (strlen(s) <= IPT_STRING_MAX_ALGO_NAME_SIZE) {
  80                 strncpy(info->algo, s, IPT_STRING_MAX_ALGO_NAME_SIZE);
  81                 return;
  82         }
  83         exit_error(PARAMETER_PROBLEM, "ALGO too long `%s'", s);
  84 }
  85
  86 static void
  87 parse_hex_string(const char *s, struct ipt_string_info *info)
  88 {
  89         int i=0, slen, sindex=0, schar;
  90         short hex_f = 0, literal_f = 0;
  91         char hextmp[3];
  92
  93         slen = strlen(s);
  94
  95         if (slen == 0) {
  96                 exit_error(PARAMETER_PROBLEM,
  97                         "STRING must contain at least one char");
  98         }
  99
 100         while (i < slen) {
 101                 if (s[i] == '\\' && !hex_f) {
 102                         literal_f = 1;
 103                 } else if (s[i] == '\\') {
 104                         exit_error(PARAMETER_PROBLEM,
 105                                 "Cannot include literals in hex data");
 106                 } else if (s[i] == '|') {
 107                         if (hex_f)
 108                                 hex_f = 0;
 109                         else {
 110                                 hex_f = 1;
 111                                 /* get past any initial whitespace just after the '|' */
 112                                 while (s[i+1] == ' ')
 113                                         i++;
 114                         }
 115                         if (i+1 >= slen)
 116                                 break;
 117                         else
 118                                 i++;  /* advance to the next character */
 119                 }
 120
 121                 if (literal_f) {
 122                         if (i+1 >= slen) {
 123                                 exit_error(PARAMETER_PROBLEM,
 124                                         "Bad literal placement at end of string");
 125                         }
 126                         info->pattern[sindex] = s[i+1];
 127                         i += 2;  /* skip over literal char */
 128                         literal_f = 0;
 129                 } else if (hex_f) {
 130                         if (i+1 >= slen) {
 131                                 exit_error(PARAMETER_PROBLEM,
 132                                         "Odd number of hex digits");
 133                         }
 134                         if (i+2 >= slen) {
 135                                 /* must end with a "|" */
 136                                 exit_error(PARAMETER_PROBLEM, "Invalid hex block");
 137                         }
 138                         if (! isxdigit(s[i])) /* check for valid hex char */
 139                                 exit_error(PARAMETER_PROBLEM, "Invalid hex char `%c'", s[i]);
 140                         if (! isxdigit(s[i+1])) /* check for valid hex char */
 141                                 exit_error(PARAMETER_PROBLEM, "Invalid hex char `%c'", s[i+1]);
 142                         hextmp[0] = s[i];
 143                         hextmp[1] = s[i+1];
 144                         hextmp[2] = '\0';
 145                         if (! sscanf(hextmp, "%x", &schar))
 146                                 exit_error(PARAMETER_PROBLEM,
 147                                         "Invalid hex char `%c'", s[i]);
 148                         info->pattern[sindex] = (char) schar;
 149                         if (s[i+2] == ' ')
 150                                 i += 3;  /* spaces included in the hex block */
 151                         else
 152                                 i += 2;
 153                 } else {  /* the char is not part of hex data, so just copy */
 154                         info->pattern[sindex] = s[i];
 155                         i++;
 156                 }
 157                 if (sindex > IPT_STRING_MAX_PATTERN_SIZE)
 158                         exit_error(PARAMETER_PROBLEM, "STRING too long `%s'", s);
 159                 sindex++;
 160         }
 161         info->patlen = sindex;
 162 }
 163
 164 #define STRING 0x1
 165 #define ALGO   0x2
 166 #define FROM   0x4
 167 #define TO     0x8
 168
 169 /* Function which parses command options; returns true if it
 170    ate an option */
 171 static int
 172 parse(int c, char **argv, int invert, unsigned int *flags,
 173       const struct ipt_entry *entry,
 174       unsigned int *nfcache,
 175       struct ipt_entry_match **match)
 176 {
 177         struct ipt_string_info *stringinfo = (struct ipt_string_info *)(*match)->data;
 178
 179         switch (c) {
 180         case '1':
 181                 if (*flags & FROM)
 182                         exit_error(PARAMETER_PROBLEM,
 183                                    "Can't specify multiple --from");
 184                 stringinfo->from_offset = atoi(optarg);
 185                 *flags |= FROM;
 186                 break;
 187         case '2':
 188                 if (*flags & TO)
 189                         exit_error(PARAMETER_PROBLEM,
 190                                    "Can't specify multiple --to");
 191                 stringinfo->to_offset = atoi(optarg);
 192                 *flags |= TO;
 193                 break;
 194         case '3':
 195                 if (*flags & ALGO)
 196                         exit_error(PARAMETER_PROBLEM,
 197                                    "Can't specify multiple --algo");
 198                 parse_algo(optarg, stringinfo);
 199                 *flags |= ALGO;
 200                 break;
 201         case '4':
 202                 if (*flags & STRING)
 203                         exit_error(PARAMETER_PROBLEM,
 204                                    "Can't specify multiple --string");
 205                 check_inverse(optarg, &invert, &optind, 0);
 206                 parse_string(argv[optind-1], stringinfo);
 207                 if (invert)
 208                         stringinfo->invert = 1;
 209                 stringinfo->patlen=strlen((char *)&stringinfo->pattern);
 210                 *flags |= STRING;
 211                 break;
 212
 213         case '5':
 214                 if (*flags & STRING)
 215                         exit_error(PARAMETER_PROBLEM,
 216                                    "Can't specify multiple --hex-string");
 217
 218                 check_inverse(optarg, &invert, &optind, 0);
 219                 parse_hex_string(argv[optind-1], stringinfo);  /* sets length */
 220                 if (invert)
 221                         stringinfo->invert = 1;
 222                 *flags |= STRING;
 223                 break;
 224
 225         default:
 226                 return 0;
 227         }
 228         return 1;
 229 }
 230
 231
 232 /* Final check; must have specified --string. */
 233 static void
 234 final_check(unsigned int flags)
 235 {
 236         if (!(flags & STRING))
 237                 exit_error(PARAMETER_PROBLEM,
 238                            "STRING match: You must specify `--string' or "
 239                            "`--hex-string'");
 240         if (!(flags & ALGO))
 241                 exit_error(PARAMETER_PROBLEM,
 242                            "STRING match: You must specify `--algo'");
 243 }
 244
 245 /* Test to see if the string contains non-printable chars or quotes */
 246 static unsigned short int
 247 is_hex_string(const char *str, const unsigned short int len)
 248 {
 249         unsigned int i;
 250         for (i=0; i < len; i++)
 251                 if (! isprint(str[i]))
 252                         return 1;  /* string contains at least one non-printable char */
 253         /* use hex output if the last char is a "\" */
 254         if ((unsigned char) str[len-1] == 0x5c)
 255                 return 1;
 256         return 0;
 257 }
 258
 259 /* Print string with "|" chars included as one would pass to --hex-string */
 260 static void
 261 print_hex_string(const char *str, const unsigned short int len)
 262 {
 263         unsigned int i;
 264         /* start hex block */
 265         printf("\"|");
 266         for (i=0; i < len; i++) {
 267                 /* see if we need to prepend a zero */
 268                 if ((unsigned char) str[i] <= 0x0F)
 269                         printf("0%x", (unsigned char) str[i]);
 270                 else
 271                         printf("%x", (unsigned char) str[i]);
 272         }
 273         /* close hex block */
 274         printf("|\" ");
 275 }
 276
 277 static void
 278 print_string(const char *str, const unsigned short int len)
 279 {
 280         unsigned int i;
 281         printf("\"");
 282         for (i=0; i < len; i++) {
 283                 if ((unsigned char) str[i] == 0x22)  /* escape any embedded quotes */
 284                         printf("%c", 0x5c);
 285                 printf("%c", (unsigned char) str[i]);
 286         }
 287         printf("\" ");  /* closing space and quote */
 288 }
 289
 290 /* Prints out the matchinfo. */
 291 static void
 292 print(const struct ipt_ip *ip,
 293       const struct ipt_entry_match *match,
 294       int numeric)
 295 {
 296         const struct ipt_string_info *info =
 297             (const struct ipt_string_info*) match->data;
 298
 299         if (is_hex_string(info->pattern, info->patlen)) {
 300                 printf("STRING match %s", (info->invert) ? "!" : "");
 301                 print_hex_string(info->pattern, info->patlen);
 302         } else {
 303                 printf("STRING match %s", (info->invert) ? "!" : "");
 304                 print_string(info->pattern, info->patlen);
 305         }
 306         printf("ALGO name %s ", info->algo);
 307         if (info->from_offset != 0)
 308                 printf("FROM %u ", info->from_offset);
 309         if (info->to_offset != 0)
 310                 printf("TO %u ", info->to_offset);
 311 }
 312
 313
 314 /* Saves the union ipt_matchinfo in parseable form to stdout. */
 315 static void
 316 save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
 317 {
 318         const struct ipt_string_info *info =
 319             (const struct ipt_string_info*) match->data;
 320
 321         if (is_hex_string(info->pattern, info->patlen)) {
 322                 printf("--hex-string %s", (info->invert) ? "! ": "");
 323                 print_hex_string(info->pattern, info->patlen);
 324         } else {
 325                 printf("--string %s", (info->invert) ? "! ": "");
 326                 print_string(info->pattern, info->patlen);
 327         }
 328         printf("--algo %s ", info->algo);
 329         if (info->from_offset != 0)
 330                 printf("--from %u ", info->from_offset);
 331         if (info->to_offset != 0)
 332                 printf("--to %u ", info->to_offset);
 333 }
 334
 335
 336 static struct iptables_match string = {
 337     .name               = "string",
 338     .version            = IPTABLES_VERSION,
 339     .size               = IPT_ALIGN(sizeof(struct ipt_string_info)),
 340     .userspacesize      = offsetof(struct ipt_string_info, config),
 341     .help               = help,
 342     .init               = init,
 343     .parse              = parse,
 344     .final_check        = final_check,
 345     .print              = print,
 346     .save               = save,
 347     .extra_opts         = opts
 348 };
 349
 350
 351 void _init(void)
 352 {
 353         register_match(&string);
 354 }