sf_snort_plugin_pcre.c

Snort为国际上著名的轻量型入侵防御系统,为国内多家著名“自主知识产权”网络安全公司所使用。

/*
 *  sf_snort_plugin_pcre.c
 *
 * 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.
 *
 * 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.
 *
 * Copyright (C) 2005 Sourcefire Inc.
 *
 * Author: Steve Sturges
 *         Andy Mullican
 *
 * Date: 5/2005
 *
 *
 * PCRE operations for dynamic rule engine
 */
#include "sf_snort_packet.h"
#include "sf_snort_plugin_api.h"
#include "sf_dynamic_engine.h"

#define DEBUG_WRAP(x)

/* Need access to the snort-isms that were passed to the engine */
extern DynamicEngineData _ded; /* sf_detection_engine.c */
extern int checkCursorInternal(void *p, int flags, int offset, u_int8_t *cursor);


int PCRESetup(Rule *rule, PCREInfo *pcreInfo)
{
    const char *error;
    int erroffset;

    pcreInfo->compiled_expr = (void *)pcre_compile(pcreInfo->expr,
                                                    pcreInfo->compile_flags,
                                                    &error,
                                                    &erroffset,
                                                    NULL);

    if (!pcreInfo->compiled_expr)
    {
        /* error doing compilation. */
        _ded.errMsg("Failed to compile PCRE in dynamic rule [%d:%d]\n",
            rule->info.genID, rule->info.sigID);
        return -1;
    }
    else
    {
        pcreInfo->compiled_extra = (void *)pcre_study(pcreInfo->compiled_expr, 0, &error);
    }

    if (error)
    {
        /* error doing study. */
        _ded.errMsg("Failed to study PCRE in dynamic rule [%d:%d]\n",
            rule->info.genID, rule->info.sigID);
        return -1;
    }

    return 0;
}

/* 
 * we need to specify the vector length for our pcre_exec call.  we only care 
 * about the first vector, which if the match is successful will include the
 * offset to the end of the full pattern match.  If we decide to store other
 * matches, make *SURE* that this is a multiple of 3 as pcre requires it.
 */
#define SNORT_PCRE_OVECTOR_SIZE 3

/** 
 * Perform a search of the PCRE data.
 * 
 * @param pcre_data structure that options and patterns are passed in
 * @param buf buffer to search
 * @param len size of buffer
 * @param start_offset initial offset into the buffer
 * @param found_offset pointer to an integer so that we know where the search ended
 *
 * *found_offset will be set to -1 when the find is unsucessful OR the routine is inverted
 *
 * @return 1 when we find the string, 0 when we don't (unless we've been passed a flag to invert)
 */
static int pcre_test(const PCREInfo *pcre_info,
                       const char *buf,
                       int len,
                       int start_offset,
                       int *found_offset)
{
    int ovector[SNORT_PCRE_OVECTOR_SIZE];
    int matched;
    int result;
    
    if(pcre_info == NULL
       || buf == NULL
       || len <= 0
       || start_offset < 0
       || start_offset >= len
       || found_offset == NULL)
    {
        DEBUG_WRAP(DebugMessage(DEBUG_PATTERN_MATCH,
                                "Returning 0 because we didn't have the required parameters!\n"););
        return 0;
    }

    *found_offset = -1;
    
    result = pcre_exec(pcre_info->compiled_expr,    /* result of pcre_compile() */
                       pcre_info->compiled_extra,   /* result of pcre_study()   */
                       buf,                         /* the subject string */
                       len,                         /* the length of the subject string */
                       start_offset,                /* start at offset 0 in the subject */
                       0,                           /* options(handled at compile time */
                       ovector,                     /* vector for substring information */
                       SNORT_PCRE_OVECTOR_SIZE);    /* number of elements in the vector */

    if(result >= 0)
    {
        matched = 1;
    }
    else if(result == PCRE_ERROR_NOMATCH)
    {
        matched = 0;
    }
    else
    {
        DEBUG_WRAP(DebugMessage(DEBUG_PATTERN_MATCH, "pcre_exec error : %d \n", result););
        return 0;
    }

    if (found_offset)
    {
        *found_offset = ovector[1];        
        DEBUG_WRAP(DebugMessage(DEBUG_PATTERN_MATCH,
                                "Setting buffer and found_offset: %p %d\n",
                                buf, found_offset););
    }

    return matched;
}

ENGINE_LINKAGE int pcreMatch(void *p, PCREInfo* pcre_info, u_int8_t **cursor)
{
    char *buffer_start;
    char *buffer_end;
    int buffer_len;
    int pcre_offset;
    int pcre_found;
    int i;
    int relative = 0;
    SFSnortPacket *sp = (SFSnortPacket *) p;

    /* Input validation */
    if (!p || !pcre_info)
    {
        return RULE_NOMATCH;
    }

    /* Input validation for cursor & relative flag */
    if (pcre_info->flags & CONTENT_RELATIVE)
    {
        if (!cursor || !*cursor)
        {
            return RULE_NOMATCH;
        }
        relative = 1;
    }

    if (pcre_info->flags & CONTENT_BUF_URI)
    {
        for (i=0;i<sp->num_uris; i++)
        {
            if (relative)
            {
                if (checkCursorInternal(p, pcre_info->flags, 0, *cursor) <= 0)
                {
                    /* Okay, cursor is NOT within this buffer... */
                    continue;
                }
                buffer_start = *cursor;
                buffer_end = _ded.uriBuffers[i]->uriBuffer +
                                _ded.uriBuffers[i]->uriLength;
                buffer_len = buffer_end - buffer_start;
            }
            else
            {
                buffer_start = _ded.uriBuffers[i]->uriBuffer;
                buffer_len = _ded.uriBuffers[i]->uriLength;
                buffer_end = buffer_start + buffer_len;
            }
            pcre_found = pcre_test(pcre_info, buffer_start, buffer_len, 0, &pcre_offset);

            if (pcre_found)
            {
                if (cursor)
                {
                    *cursor = buffer_start + pcre_offset;
                }
                return RULE_MATCH;
            }
        }

        return RULE_NOMATCH;
    }

    if (relative)
    {
        if (checkCursorInternal(p, pcre_info->flags, 0, *cursor) <= 0)
        {
            return RULE_NOMATCH;
        }

        if ((pcre_info->flags & CONTENT_BUF_NORMALIZED) && (sp->flags & FLAG_ALT_DECODE))
        {
            buffer_start = _ded.altBuffer;
            buffer_end = buffer_start + sp->normalized_payload_size;
        }
        else
        {
            buffer_start = sp->payload;
            buffer_end = buffer_start + sp->payload_size;
        }
        buffer_len = buffer_end - buffer_start;
        buffer_start = *cursor;
    }
    else
    {
        if ((pcre_info->flags & CONTENT_BUF_NORMALIZED) && (sp->flags & FLAG_ALT_DECODE))
        {
            buffer_start = _ded.altBuffer;
            buffer_len = sp->normalized_payload_size;
        }
        else
        {
            buffer_start = sp->payload;
            buffer_len = sp->payload_size;
        }
        buffer_end = buffer_start + buffer_len;
    }

    pcre_found = pcre_test(pcre_info, buffer_start, buffer_len, 0, &pcre_offset);

    if (pcre_found)
    {
        if (cursor)
        {
            *cursor = buffer_start + pcre_offset;
        }
    }

    if (pcre_found)
        return RULE_MATCH;

    return RULE_NOMATCH;
}