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

   1 /* libipt_TCPLAG.c -- module for iptables to interface with TCPLAG target
   2  * Copyright (C) 2002 Telford Tendys <telford@triode.net.au>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  17  */
  18
  19 /*
  20  * Shared library add-on to iptables for TCPLAG target control
  21  *
  22  * This allows installation and removal of the TCPLAG target
  23  * Note that there is a lot more commentary in this file than
  24  * the average libipt target (i.e. more than none) but these
  25  * are just my deductions based on examination of the source
  26  * and
  27  */
  28 #include <stdio.h>
  29 #include <netdb.h>
  30 #include <string.h>
  31 #include <stdlib.h>
  32 #include <syslog.h>
  33 #include <getopt.h>
  34 #include <iptables.h>
  35 #include <linux/netfilter_ipv4/ip_tables.h>
  36 #include <linux/netfilter_ipv4/ipt_TCPLAG.h>
  37
  38 /*
  39  * This merely dumps out text for the user
  40  * (saves keeping the manpage up to date)
  41  */
  42 static void help( void )
  43 {
  44         printf( "TCPLAG options:\n"
  45                         " --log-level=n    Set the syslog level to n (integer 0 to 7)\n\n"
  46                         " --log-prefix=xx  Prefix log messages with xx\n" );
  47 }
  48
  49 /*
  50  * See "man getopt_long" for an explanation of this structure
  51  *
  52  * If one of our options DOES happen to come up then we get
  53  * a callback into parse(), our vals must not overlap with any
  54  * normal iptables short options (I think) because there is only
  55  * one actual options handler and it can't tell whose options it
  56  * is really looking at unless they are all distinct.
  57  *
  58  * These are exactly the same as the LOG target options
  59  * and have the same purpose.
  60  */
  61 static const struct option opts[] =
  62 {
  63         { "log-level",     1, 0, '!' },
  64         { "log-prefix",    1, 0, '#' },
  65         { 0 }
  66 };
  67
  68 /*
  69  * This gives us a chance to install some initial values in
  70  * our own private data structure (which is at t->data).
  71  * Probably we could fiddle with t->tflags too but there is
  72  * no great advantage in doing so.
  73  */
  74 static void init( struct ipt_entry_target *t, unsigned int *nfcache )
  75 {
  76         struct ipt_tcplag *el = (struct ipt_tcplag *)t->data;
  77         memset( el, 0, sizeof( struct ipt_tcplag ));
  78         el->level = 4; /* Default to warning level */
  79         strcpy( el->prefix, "TCPLAG:" ); /* Give a reasonable default prefix */
  80 }
  81
  82 /*
  83  * It doesn't take much thought to see how little thought has gone into
  84  * this particular API. However, to add to that I'd just like to say that
  85  * it can be made to work and small miracles are still miracles.
  86  *
  87  * The input parameters are as follows:
  88  *
  89  *  c      --  the 'val' from opts[] above, could possibly be something
  90  *             we cannot recognise in which case return(0).
  91  *             If we do recognise it then return(1).
  92  *
  93  *  argv   --  in case we want to take parameters from the command line,
  94  *             not sure how to safely ensure that the parameter that
  95  *             we want to take will really exist, presumably getopt_long()
  96  *             will have already checked such things (what about optional
  97  *             parameters huh?).
  98  *
  99  *  invert --  if the option parameter had '!' in front of it, usually this
 100  *             would inversion of the matching sense but I don't think it
 101  *             is useful in the case of targets.
 102  *
 103  *  flags  --  always (*target)->tflags for those who feel it is better
 104  *             to access this field indirectly <shrug> starts of
 105  *             zero for a fresh target, gets fed into final_check().
 106  *
 107  *  entry  --  apparently useless
 108  *
 109  *  target --  the record that holds data about this target,
 110  *             most importantly, our private data is (*target)->data
 111  *             (this has already been malloced for us).
 112  */
 113 static int parse( int c, char **argv, int invert, unsigned int *flags,
 114                                   const struct ipt_entry *entry, struct ipt_entry_target **target )
 115 {
 116         struct ipt_tcplag *el = (struct ipt_tcplag *)( *target )->data;
 117 /*
 118  * Yeah, we could complain about options being issued twice but
 119  * is it really worth the trouble? Will it make the world a better place?
 120  */
 121         switch( c )
 122         {
 123 /*
 124  * I really can't be bothered with the syslog naming convention,
 125  * it isn't terribly useful anyhow.
 126  */
 127                 case '!':
 128                         el->level = strtol( optarg, 0, 10 );
 129                         return( 1 );
 130 /*
 131  * 15 chars should be plenty
 132  */
 133                 case '#':
 134                         strncpy( el->prefix, optarg, 15 );
 135                         el->prefix[ 14 ] = 0; /* Force termination */
 136                         return( 1 );
 137         }
 138         return( 0 );
 139 }
 140
 141 /*
 142  * This gets given the (*target)->tflags value from
 143  * the parse() above and it gets called after all the
 144  * parsing of options is completed. Thus if one option
 145  * requires another option you can test the flags and
 146  * decide whether everything is in order.
 147  *
 148  * If there is a problem then do something like:
 149  *              exit_error( PARAMETER_PROBLEM, "foobar parameters detected in TCPLAG target");
 150  *
 151  * In this case, no errors are possible
 152  */
 153 static void final_check( unsigned int flags ) { }
 154 /*
 155  * This print is for the purpose of user-readable display
 156  * such as what "iptables -L" would give. The notes in
 157  * iptables.h say that target could possibly be a null pointer
 158  * but coding of the various libipt_XX.c modules suggests
 159  * that it is safe to presume target is correctly initialised.
 160  */
 161 static void print(const struct ipt_ip *ip, const struct ipt_entry_target *target, int numeric)
 162 {
 163         const struct ipt_tcplag *el = (const struct ipt_tcplag *)target->data;
 164         printf("TCPLAG <%d>", el->level );
 165         if( el->prefix[ 0 ])
 166         {
 167                 printf( "%s", el->prefix );
 168         }
 169 }
 170
 171 /*
 172  * As above but command-line style printout
 173  * (machine-readable for restoring table)
 174  */
 175 static void save( const struct ipt_ip *ip, const struct ipt_entry_target *target )
 176 {
 177         const struct ipt_tcplag *el = (const struct ipt_tcplag *)target->data;
 178         printf("TCPLAG --log-level=%d", el->level );
 179         if( el->prefix[ 0 ])
 180         {
 181 /*
 182  * FIXME: Should have smarter quoting
 183  */
 184                 printf( " --log-prefix='%s'", el->prefix );
 185         }
 186 }
 187
 188 /*
 189  * The version must match the iptables version exactly
 190  * which is a big pain, could use `iptables -V` in makefile
 191  * but we can't guarantee compatibility with all iptables
 192  * so we are stuck with only supporting one particular version.
 193  */
 194 static struct iptables_target targ =
 195 {
 196 next:             0,
 197 name:             "TCPLAG",
 198 version:          IPTABLES_VERSION,
 199 size:             IPT_ALIGN( sizeof( struct ipt_tcplag )),
 200 userspacesize:    IPT_ALIGN( sizeof( struct ipt_tcplag )),
 201 help:             &help,
 202 init:             &init,
 203 parse:            &parse,
 204 final_check:      &final_check,
 205 print:            &print,
 206 save:             &save,
 207 extra_opts:       opts
 208 };
 209
 210 /*
 211  * Always nervous trusting _init() but oh well that is the standard
 212  * so have to go ahead and use it. This registers your target into
 213  * the list of available targets so that your options become available.
 214  */
 215 void _init( void ) { register_target( &targ ); }