detect-prefilter.c

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/* Copyright (C) 2007-2016 Open Information Security Foundation
 *
 * You can copy, redistribute or modify this Program under the terms of
 * the GNU General Public License version 2 as published by the Free
 * Software Foundation.
 *
 * 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
 * version 2 along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */
 
/**
 * \file
 *
 * \author Victor Julien <victor@inliniac.net>
 *
 * Implements the prefilter keyword
 */
 
#include "suricata-common.h"
#include "decode.h"
 
#include "detect.h"
#include "detect-parse.h"
#include "detect-content.h"
#include "detect-app-layer-protocol.h"
#include "detect-engine-mpm.h"
#include "detect-prefilter.h"
#include "util-debug.h"
 
static int DetectPrefilterSetup (DetectEngineCtx *, Signature *, const char *);
 
void DetectPrefilterRegister(void)
{
    sigmatch_table[DETECT_PREFILTER].name = "prefilter";
    sigmatch_table[DETECT_PREFILTER].desc = "force a condition to be used as prefilter";
    sigmatch_table[DETECT_PREFILTER].url = "/rules/prefilter-keywords.html#prefilter";
    sigmatch_table[DETECT_PREFILTER].Setup = DetectPrefilterSetup;
    sigmatch_table[DETECT_PREFILTER].flags |= SIGMATCH_NOOPT;
}
 
/**
 *  \internal
 *  \brief Apply the prefilter keyword to the last match
 *  \param det_ctx detection engine ctx
 *  \param s signature
 *  \param nullstr should be null
 *  \retval 0 ok
 *  \retval -1 failure
 */
static int DetectPrefilterSetup (DetectEngineCtx *de_ctx, Signature *s, const char *nullstr)
{
    SCEnter();
 
    if (nullstr != NULL) {
        SCLogError("prefilter has value");
        SCReturnInt(-1);
    }
 
    if (s->flags & SIG_FLAG_PREFILTER) {
        SCLogError("prefilter already set");
        SCReturnInt(-1);
    }
 
    SigMatch *sm = DetectGetLastSM(s);
    if (sm == NULL) {
        SCLogError("prefilter needs preceding match");
        SCReturnInt(-1);
    }
 
    /* if the sig match is content, prefilter should act like
     * 'fast_pattern' w/o options. */
    if (sm->type == DETECT_CONTENT) {
        if (s->flags & SIG_FLAG_TXBOTHDIR && s->init_data->curbuf != NULL) {
            if (s->init_data->init_flags & SIG_FLAG_INIT_TXDIR_STREAMING_TOSERVER) {
                if (DetectBufferToClient(de_ctx, s->init_data->curbuf->id, s->alproto)) {
                    SCLogError("prefilter cannot be used on to_client keyword for "
                               "transactional rule %u",
                            s->id);
                    SCReturnInt(-1);
                } else {
                    s->init_data->init_flags |= SIG_FLAG_INIT_TXDIR_FAST_TOCLIENT;
                }
            }
        }
 
        DetectContentData *cd = (DetectContentData *)sm->ctx;
        if ((cd->flags & DETECT_CONTENT_NEGATED) &&
                ((cd->flags & DETECT_CONTENT_DISTANCE) ||
                 (cd->flags & DETECT_CONTENT_WITHIN) ||
                 (cd->flags & DETECT_CONTENT_OFFSET) ||
                 (cd->flags & DETECT_CONTENT_DEPTH)))
        {
            SCLogError("prefilter; cannot be "
                       "used with negated content, along with relative modifiers");
            SCReturnInt(-1);
        }
        cd->flags |= DETECT_CONTENT_FAST_PATTERN;
    } else {
        if (sigmatch_table[sm->type].SupportsPrefilter == NULL) {
            SCLogError("prefilter is not supported for %s", sigmatch_table[sm->type].name);
            SCReturnInt(-1);
        }
 
        /* A multi-value app-layer-protocol keyword stores its values in a
         * bitmask that the single-valued prefilter bucket key can't carry, so
         * forcing prefilter would bucket the rule under ALPROTO_UNKNOWN and
         * silently never match. */
        if (sm->type == DETECT_APP_LAYER_PROTOCOL &&
                ((const DetectAppLayerProtocolData *)sm->ctx)->is_list) {
            SCLogError("prefilter is not supported for multi-value app-layer-protocol");
            SCReturnInt(-1);
        }
 
        /* make sure setup function runs for this type. */
        de_ctx->sm_types_prefilter[sm->type] = true;
    }
 
    s->init_data->prefilter_sm = sm;
    SCLogDebug(
            "sid %u: prefilter is on \"%s\" (%u)", s->id, sigmatch_table[sm->type].name, sm->type);
 
    SCReturnInt(0);
}