spp_rpc_decode.c

著名的入侵检测系统snort的最新版本的源码

/*
** Copyright (C) 1998-2002 Martin Roesch <[e-mail]>
**
** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License Version 2 as
** published by the Free Software Foundation.  You may not use, modify or
** distribute this program under any other version of the GNU General
** Public License.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
** GNU General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with this program; if not, write to the Free Software
** Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/

/* $Id$ */
/* spp_rpc_decode 
 * 
 * Purpose:
 *
 * This preprocessor normalizes the RPC requests from remote machines by
 * converting all fragments into one continous stream.
 * This is very useful for doing things like defeating hostile attackers
 * trying to stealth themselves from IDSs by fragmenting the request so the
 * string 0186A0 is broken up.
 *
 * Arguments:
 *   
 * This plugin takes a list of integers representing the TCP ports that the
 * user is interested in having normalized
 *
 * Effect:
 *
 * Changes the data in the packet payload and changes
 * p->dsize to reflect the new (smaller) payload size.
 *
 * Comments:
 *
 */

#ifdef HAVE_CONFIG_H	 
#include "config.h"	 
#endif

#include <sys/types.h>
#include <stdlib.h>
#include <ctype.h>

#ifdef HAVE_STRINGS_H	 
#include <strings.h>	 
#endif

#include "decode.h"
#include "plugbase.h"
#include "parser.h"
#include "log.h"
#include "debug.h"
#include "util.h"

#include "mstring.h"
#include "snort.h"
#include "detect.h"
#include "log.h"
#include "generators.h"
#include "event_queue.h"

#include "profiler.h"
#include "bounds.h"
#include "strlcatu.h"

extern char *file_name;
extern int file_line;
extern int do_detect;
extern u_int8_t DecodeBuffer[DECODE_BLEN];

#define OPT_ALERT_FRAGMENTS "alert_fragments"
#define OPT_ALERT_MULTIPLE_REQUESTS "no_alert_multiple_requests"
#define OPT_ALERT_LARGE_FRAGMENTS "no_alert_large_fragments"
#define OPT_ALERT_INCOMPLETE "no_alert_incomplete"

#define TEXT_ALERT_MULTIPLE_REQUESTS "alert_multiple_requests"
#define TEXT_ALERT_LARGE_FRAGMENTS "alert_large_fragments"
#define TEXT_ALERT_INCOMPLETE "alert_incomplete"

#define RPC_CLASS DECODE_CLASS /* use the same classification as the other decoder alerts */

typedef struct _RpcDecodeData
{
    char alert_fragments;    /* Alert when we see ANY fragmented RPC requests */
    char alert_incomplete; /* Alert when we don't see all of a request in one packet */
    char alert_multi;        /* Alert when we see multiple requests in one packet */
    char alert_large;        /* Alert when we see multiple requests in one packet */
} RpcDecodeData;

static RpcDecodeData rpcpreprocdata; /* Configuration Set */
static char RpcDecodePorts[65536/8];

#ifdef PERF_PROFILING
PreprocStats rpcdecodePerfStats;
#endif

void RpcDecodeInit(char *);
void RpcDecodeInitIgnore(char *);
void PreprocRpcDecode(Packet *, void *);
void SetRpcPorts(char *);
int ConvertRPC(Packet *);

/*
 * Function: SetupRpcDecode()
 *
 * Purpose: Registers the preprocessor keyword and initialization 
 *          function into the preprocessor list.
 *
 * Arguments: None.
 *
 * Returns: void function
 *
 */
void SetupRpcDecode(void)
{
    /* link the preprocessor keyword to the init function in 
       the preproc list */
    RegisterPreprocessor("rpc_decode", RpcDecodeInit);

    DEBUG_WRAP(DebugMessage(DEBUG_RPC,"Preprocessor: RpcDecode in setup...\n"););
}


/*
 * Function: RpcDecodeInit(char *)
 *
 * Purpose: Processes the args sent to the preprocessor, sets up the
 *          port list, links the processing function into the preproc
 *          function list
 *
 * Arguments: args => ptr to argument string
 *
 * Returns: void function
 *
 */
void RpcDecodeInit(char *args)
{
    DEBUG_WRAP(DebugMessage(DEBUG_RPC,"Preprocessor: RpcDecode Initialized\n"););

    bzero(&rpcpreprocdata,sizeof(RpcDecodeData));

    /* turn on the following alerts by default */
    rpcpreprocdata.alert_multi = 1;
    rpcpreprocdata.alert_incomplete = 1;
    rpcpreprocdata.alert_large = 1;
    
    /* parse the argument list into a list of ports to normalize */
    SetRpcPorts((char *)args);

    /* Set the preprocessor function into the function list */
    AddFuncToPreprocList(PreprocRpcDecode, PRIORITY_APPLICATION, PP_RPCDECODE);

#ifdef PREF_PROFILING
    RegisterPreprocessorProfile("rpcdecode", &rpcdecodePerfStats, 0, &totalPerfStats);
#endif
}

/*
 * Function: SetRpcPorts(char *)
 *
 * Purpose: Reads the list of port numbers from the argument string and
 *          parses them into the port list data struct
 *
 * Arguments: portlist => argument list
 *
 * Returns: void function
 *
 */
void SetRpcPorts(char *portlist)
{
    char portstr[STD_BUF];
    char **toks;
    int is_reset = 0;
    int num_toks;
    int num;

    if(portlist == NULL || *portlist == '\0')
    {
        portlist = "111 32771";
    }

    /* tokenize the argument list */
    toks = mSplit(portlist, " ", 31, &num_toks, '\\');

    LogMessage("rpc_decode arguments:\n");
    
    /* convert the tokens and place them into the port list */
    for(num = 0; num < num_toks; num++)
    {
        if(isdigit((int)toks[num][0]))
        {
            char *num_p = NULL; /* used to determine last position in string */
            long t_num;

            t_num = strtol(toks[num], &num_p, 10);

            if(*num_p != '\0')
            {
                FatalError("ERROR %s(%d) => Port Number invalid format: %s\n",
                           file_name, file_line, toks[num]);
            }
            else if(t_num < 0 || t_num > 65535)
            {
	        FatalError("ERROR %s(%d) => Port Number out of range: %ld\n",
                           file_name, file_line, t_num);
            }

            /* user specified a legal port number and it should override the default
               port list, so reset it unless already done */
            if(!is_reset)
            {
                bzero(&RpcDecodePorts, sizeof(RpcDecodePorts));
                portstr[0] = '\0';
                is_reset = 1;
            }

            /* mark this port as being interesting using some portscan2-type voodoo,
               and also add it to the port list string while we're at it so we can
               later print out all the ports with a single LogMessage() */
            RpcDecodePorts[(t_num/8)] |= 1<<(t_num%8);
            strlcat(portstr, toks[num], STD_BUF - 1);
            strlcat(portstr, " ", STD_BUF - 1);
        }
        else if(!strcasecmp(OPT_ALERT_MULTIPLE_REQUESTS,toks[num]))
        {
            rpcpreprocdata.alert_multi = 0;
        }
        else if(!strcasecmp(OPT_ALERT_INCOMPLETE,toks[num]))
        {
            rpcpreprocdata.alert_incomplete = 0;
        }
        else if(!strcasecmp(OPT_ALERT_LARGE_FRAGMENTS,toks[num]))
        {
            rpcpreprocdata.alert_large = 0;
        }
        else if(!strcasecmp(OPT_ALERT_FRAGMENTS,toks[num]))
        {
            rpcpreprocdata.alert_fragments = 1;
        }
        else
        {
            FatalError("ERROR %s(%d) => Unknown argument to rpc_decode "
                       "preprocessor: \"%s\"\n",
                       file_name, file_line, toks[num]);
        }
    }

    mSplitFree(&toks, num_toks);

    /* print out final port list */
    LogMessage("    Ports to decode RPC on: %s\n", portstr);
    LogMessage("    %s: %s\n", OPT_ALERT_FRAGMENTS, rpcpreprocdata.alert_fragments ? "ACTIVE": "INACTIVE");
    LogMessage("    %s: %s\n", TEXT_ALERT_LARGE_FRAGMENTS, rpcpreprocdata.alert_large ? "ACTIVE": "INACTIVE");
    LogMessage("    %s: %s\n", TEXT_ALERT_INCOMPLETE, rpcpreprocdata.alert_incomplete ? "ACTIVE": "INACTIVE");
    LogMessage("    %s: %s\n", TEXT_ALERT_MULTIPLE_REQUESTS, rpcpreprocdata.alert_multi ? "ACTIVE": "INACTIVE");
}                                                                               
   

/*
 * Function: PreprocRpcDecode(Packet *)
 *
 * Purpose: Inspects the packet's payload for fragment records and 
 *          converts them into one infragmented record.
 *
 * Arguments: p => pointer to the current packet data struct 
 *
 * Returns: void function
 *
 */
void PreprocRpcDecode(Packet *p, void *context)
{
    int ret = 0; /* return code for ConvertRPC */
    PROFILE_VARS;
    
    DEBUG_WRAP(DebugMessage(DEBUG_RPC,"rpc decoder init on %d bytes\n", p->dsize););

    /* check to make sure we're talking TCP and that the TWH has already
       completed before processing anything */
    if(!PacketIsTCP(p))
    {
        DEBUG_WRAP(DebugMessage(DEBUG_RPC,"It isn't TCP session traffic\n"););
        return;
    }

    if((snort_runtime.capabilities.stateful_inspection == 1) &&
       (p->packet_flags & PKT_FROM_SERVER))
    {
        DEBUG_WRAP(DebugMessage(DEBUG_RPC,"This is from a server\n"););
        return;