--- /dev/null +++ b/extensions/libxt_layer7.c @@ -0,0 +1,368 @@ +/* + Shared library add-on to iptables for layer 7 matching support. + + By Matthew Strait , Oct 2003-Aug 2008. + + http://l7-filter.sf.net + + This program is free software; you can redistribute it and/or + modify it under the terms of the GNU General Public License + as published by the Free Software Foundation; either version + 2 of the License, or (at your option) any later version. + http://www.gnu.org/licenses/gpl.txt +*/ + +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include + +#include +#include + +#define MAX_FN_LEN 256 + +static char l7dir[MAX_FN_LEN] = "\0"; + +/* Function which prints out usage message. */ +static void help(void) +{ + printf( + "layer7 match options:\n" + " --l7dir : Look for patterns here instead of /etc/l7-protocols/\n" + " (--l7dir must be specified before --l7proto if used)\n" + "[!] --l7proto : Match named protocol using /etc/l7-protocols/.../name.pat\n"); +} + +static const struct option opts[] = { + { .name = "l7proto", .has_arg = 1, .val = 'p' }, + { .name = "l7dir", .has_arg = 1, .val = 'd' }, + { .name = NULL } +}; + +/* reads filename, puts protocol info into layer7_protocol_info, number of protocols to numprotos */ +static int parse_protocol_file(char * filename, const char * protoname, struct xt_layer7_info *info) +{ + FILE * f; + char * line = NULL; + size_t len = 0; + + enum { protocol, pattern, done } datatype = protocol; + + f = fopen(filename, "r"); + + if(!f) + return 0; + + while(getline(&line, &len, f) != -1) + { + if(strlen(line) < 2 || line[0] == '#') + continue; + + /* strip the pesky newline... */ + if(line[strlen(line) - 1] == '\n') + line[strlen(line) - 1] = '\0'; + + if(datatype == protocol) + { + /* Ignore everything on the line beginning with the + first space or tab . For instance, this allows the + protocol line in http.pat to be "http " (or + "http I am so cool") instead of just "http". */ + if(strchr(line, ' ')){ + char * space = strchr(line, ' '); + space[0] = '\0'; + } + if(strchr(line, '\t')){ + char * space = strchr(line, '\t'); + space[0] = '\0'; + } + + /* sanity check. First non-comment non-blank + line must be the same as the file name. */ + if(strcmp(line, protoname)) + xtables_error(OTHER_PROBLEM, + "Protocol name (%s) doesn't match file name (%s). Bailing out\n", + line, filename); + + if(strlen(line) >= MAX_PROTOCOL_LEN) + xtables_error(PARAMETER_PROBLEM, + "Protocol name in %s too long!", filename); + strncpy(info->protocol, line, MAX_PROTOCOL_LEN); + + datatype = pattern; + } + else if(datatype == pattern) + { + if(strlen(line) >= MAX_PATTERN_LEN) + xtables_error(PARAMETER_PROBLEM, "Pattern in %s too long!", filename); + strncpy(info->pattern, line, MAX_PATTERN_LEN); + + datatype = done; + break; + } + else + xtables_error(OTHER_PROBLEM, "Internal error"); + } + + if(datatype != done) + xtables_error(OTHER_PROBLEM, "Failed to get all needed data from %s", filename); + + if(line) free(line); + fclose(f); + + return 1; +} + +static int hex2dec(char c) +{ + switch (c) + { + case '0' ... '9': + return c - '0'; + case 'a' ... 'f': + return c - 'a' + 10; + case 'A' ... 'F': + return c - 'A' + 10; + default: + xtables_error(OTHER_PROBLEM, "hex2dec: bad value!\n"); + return 0; + } +} + +/* takes a string with \xHH escapes and returns one with the characters +they stand for */ +static char * pre_process(char * s) +{ + char * result = malloc(strlen(s) + 1); + int sindex = 0, rrindex = 0; + while( sindex < strlen(s) ) + { + if( sindex + 3 < strlen(s) && + s[sindex] == '\\' && s[sindex+1] == 'x' && + isxdigit(s[sindex + 2]) && isxdigit(s[sindex + 3]) ) + { + /* carefully remember to call tolower here... */ + result[rrindex] = tolower( hex2dec(s[sindex + 2])*16 + + hex2dec(s[sindex + 3] ) ); + + switch ( result[rrindex] ) + { + case 0x24: + case 0x28: + case 0x29: + case 0x2a: + case 0x2b: + case 0x2e: + case 0x3f: + case 0x5b: + case 0x5c: + case 0x5d: + case 0x5e: + case 0x7c: + fprintf(stderr, + "Warning: layer7 regexp contains a control character, %c, in hex (\\x%c%c).\n" + "I recommend that you write this as %c or \\%c, depending on what you meant.\n", + result[rrindex], s[sindex + 2], s[sindex + 3], result[rrindex], result[rrindex]); + break; + case 0x00: + fprintf(stderr, + "Warning: null (\\x00) in layer7 regexp. A null terminates the regexp string!\n"); + break; + default: + break; + } + + + sindex += 3; /* 4 total */ + } + else + result[rrindex] = tolower(s[sindex]); + + sindex++; + rrindex++; + } + result[rrindex] = '\0'; + + return result; +} + +#define MAX_SUBDIRS 128 +static char ** readl7dir(char * dirname) +{ + DIR * scratchdir; + struct dirent ** namelist; + char ** subdirs = malloc(MAX_SUBDIRS * sizeof(char *)); + + int n, d = 1; + subdirs[0] = ""; + + n = scandir(dirname, &namelist, 0, alphasort); + + if (n < 0) + { + perror("scandir"); + xtables_error(OTHER_PROBLEM, "Couldn't open %s\n", dirname); + } + else + { + while(n--) + { + char fulldirname[MAX_FN_LEN]; + + snprintf(fulldirname, MAX_FN_LEN, "%s/%s", dirname, namelist[n]->d_name); + + if((scratchdir = opendir(fulldirname)) != NULL) + { + closedir(scratchdir); + + if(!strcmp(namelist[n]->d_name, ".") || + !strcmp(namelist[n]->d_name, "..")) + /* do nothing */ ; + else + { + subdirs[d] = malloc(strlen(namelist[n]->d_name) + 1); + strcpy(subdirs[d], namelist[n]->d_name); + d++; + if(d >= MAX_SUBDIRS - 1) + { + fprintf(stderr, + "Too many subdirectories, skipping the rest!\n"); + break; + } + } + } + free(namelist[n]); + } + free(namelist); + } + + subdirs[d] = NULL; + + return subdirs; +} + +static void parse_layer7_protocol(const char *s, struct xt_layer7_info *info) +{ + char filename[MAX_FN_LEN]; + char * dir = NULL; + char ** subdirs; + int n = 0, done = 0; + + if(strlen(l7dir) > 0) dir = l7dir; + else dir = "/etc/l7-protocols"; + + subdirs = readl7dir(dir); + + while(subdirs[n] != NULL) + { + int c = snprintf(filename, MAX_FN_LEN, "%s/%s/%s.pat", dir, subdirs[n], s); + + if(c > MAX_FN_LEN) + xtables_error(OTHER_PROBLEM, + "Filename beginning with %s is too long!\n", filename); + + /* read in the pattern from the file */ + if(parse_protocol_file(filename, s, info)){ + done = 1; + break; + } + + n++; + } + + if(!done) + xtables_error(OTHER_PROBLEM, + "Couldn't find a pattern definition file for %s.\n", s); + + /* process \xHH escapes and tolower everything. (our regex lib has no + case insensitivity option.) */ + strncpy(info->pattern, pre_process(info->pattern), MAX_PATTERN_LEN); +} + +/* Function which parses command options; returns true if it ate an option */ +static int parse(int c, char **argv, int invert, unsigned int *flags, + const void *entry, struct xt_entry_match **match) +{ + struct xt_layer7_info *layer7info = + (struct xt_layer7_info *)(*match)->data; + + switch (c) { + case 'p': + parse_layer7_protocol(argv[optind-1], layer7info); + if (invert) + layer7info->invert = true; + *flags = 1; + break; + + case 'd': + if(strlen(argv[optind-1]) >= MAX_FN_LEN) + xtables_error(PARAMETER_PROBLEM, "directory name too long\n"); + + strncpy(l7dir, argv[optind-1], MAX_FN_LEN); + + *flags = 1; + break; + + default: + return 0; + } + + return 1; +} + +/* Final check; must have specified --l7proto */ +static void final_check(unsigned int flags) +{ + if (!flags) + xtables_error(PARAMETER_PROBLEM, + "LAYER7 match: You must specify `--l7proto'"); +} + +static void print_protocol(char s[], int invert, int numeric) +{ + fputs("l7proto ", stdout); + if (invert) fputc('!', stdout); + printf("%s ", s); +} + +/* Prints out the matchinfo. */ +static void print(const void *ip, + const struct xt_entry_match *match, + int numeric) +{ + printf("LAYER7 "); + print_protocol(((struct xt_layer7_info *)match->data)->protocol, + ((struct xt_layer7_info *)match->data)->invert, numeric); +} +/* Saves the union ipt_matchinfo in parsable form to stdout. */ +static void save(const void *ip, const struct xt_entry_match *match) +{ + const struct xt_layer7_info *info = + (const struct xt_layer7_info*) match->data; + + printf("--l7proto %s%s ", (info->invert)? "! ":"", info->protocol); +} + +static struct xtables_match layer7 = { + .family = AF_INET, + .name = "layer7", + .version = XTABLES_VERSION, + .size = XT_ALIGN(sizeof(struct xt_layer7_info)), + .userspacesize = XT_ALIGN(sizeof(struct xt_layer7_info)), + .help = &help, + .parse = &parse, + .final_check = &final_check, + .print = &print, + .save = &save, + .extra_opts = opts +}; + +void _init(void) +{ + xtables_register_match(&layer7); +} --- /dev/null +++ b/extensions/libxt_layer7.man @@ -0,0 +1,14 @@ +This module matches packets based on the application layer data of +their connections. It uses regular expression matching to compare +the application layer data to regular expressions found it the layer7 +configuration files. This is an experimental module which can be found at +http://l7-filter.sf.net. It takes two options. +.TP +.BI "--l7proto " "\fIprotocol\fP" +Match the specified protocol. The protocol name must match a file +name in /etc/l7-protocols/ or one of its first-level child directories. +.TP +.BI "--l7dir " "\fIdirectory\fP" +Use \fIdirectory\fP instead of /etc/l7-protocols/. This option must be +specified before --l7proto. +