/* Copyright (C) 2007-2019 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>

 * \author Anoop Saldanha <anoopsaldanha@gmail.com>

 *

 * Implements the depth keyword.

 */

#include "suricata-common.h"

#include "decode.h"

#include "detect.h"

#include "detect-parse.h"

#include "detect-content.h"

#include "detect-uricontent.h"

#include "detect-byte.h"

#include "detect-byte-extract.h"

#include "detect-depth.h"

#include "flow-var.h"

#include "app-layer.h"

#include "util-byte.h"

#include "util-debug.h"

static int DetectDepthSetup (DetectEngineCtx *, Signature *, const char *);

static int DetectStartsWithSetup (DetectEngineCtx *, Signature *, const char *);

void DetectDepthRegister (void)

{

    sigmatch_table[DETECT_DEPTH].name = "depth";

    sigmatch_table[DETECT_DEPTH].desc = "designate how many bytes from the beginning of the payload will be checked";

    sigmatch_table[DETECT_DEPTH].url = "/rules/payload-keywords.html#depth";

    sigmatch_table[DETECT_DEPTH].Match = NULL;

    sigmatch_table[DETECT_DEPTH].Setup = DetectDepthSetup;

    sigmatch_table[DETECT_DEPTH].Free  = NULL;

    sigmatch_table[DETECT_STARTS_WITH].name = "startswith";

    sigmatch_table[DETECT_STARTS_WITH].desc = "pattern must be at the start of a buffer (same as 'depth:<pattern len>')";

    sigmatch_table[DETECT_STARTS_WITH].url = "/rules/payload-keywords.html#startswith";

    sigmatch_table[DETECT_STARTS_WITH].Setup = DetectStartsWithSetup;

    sigmatch_table[DETECT_STARTS_WITH].flags |= SIGMATCH_NOOPT;

}

static int DetectDepthSetup (DetectEngineCtx *de_ctx, Signature *s, const char *depthstr)

{

    const char *str = depthstr;

    SigMatch *pm = NULL;

    int ret = -1;

    /* retrieve the sm to apply the depth against */

    pm = DetectGetLastSMFromLists(s, DETECT_CONTENT, -1);

    if (pm == NULL) {

        SCLogError("depth needs "

                   "preceding content, uricontent option, http_client_body, "

                   "http_server_body, http_header option, http_raw_header option, "

                   "http_method option, http_cookie, http_raw_uri, "

                   "http_stat_msg, http_stat_code, http_user_agent, "

                   "http_host, http_raw_host or "

                   "file_data/dce_stub_data sticky buffer options.");

        goto end;

    }

    /* verify other conditions. */

    DetectContentData *cd = (DetectContentData *)pm->ctx;

    if (cd->flags & DETECT_CONTENT_DEPTH) {

        SCLogError("can't use multiple depths for the same content.");

        goto end;

    }

    if ((cd->flags & DETECT_CONTENT_WITHIN) || (cd->flags & DETECT_CONTENT_DISTANCE)) {

        SCLogError("can't use a relative "

                   "keyword like within/distance with a absolute "

                   "relative keyword like depth/offset for the same "

                   "content.");

        goto end;

    }

    if (cd->flags & DETECT_CONTENT_NEGATED && cd->flags & DETECT_CONTENT_FAST_PATTERN) {

        SCLogError("can't have a relative "

                   "negated keyword set along with 'fast_pattern'.");

        goto end;

    }

    if (cd->flags & DETECT_CONTENT_FAST_PATTERN_ONLY) {

        SCLogError("can't have a relative "

                   "keyword set along with 'fast_pattern:only;'.");

        goto end;

    }

    if (str[0] != '-' && isalpha((unsigned char)str[0])) {

        DetectByteIndexType index;

        if (!DetectByteRetrieveSMVar(str, s, &index)) {

            SCLogError("unknown byte_ keyword var "

                       "seen in depth - %s.",

                    str);

            goto end;

        }

        cd->depth = index;

        cd->flags |= DETECT_CONTENT_DEPTH_VAR;

    } else {

        if (StringParseUint16(&cd->depth, 0, 0, str) < 0)

        {

            SCLogError("invalid value for depth: %s.", str);

            goto end;

        }

        if (cd->depth < cd->content_len) {

            SCLogError("depth:%u smaller than "

                       "content of len %u.",

                    cd->depth, cd->content_len);

            return -1;

        }

        /* Now update the real limit, as depth is relative to the offset */

        cd->depth += cd->offset;

    }

    cd->flags |= DETECT_CONTENT_DEPTH;

    ret = 0;

 end:

    return ret;

}

static int DetectStartsWithSetup (DetectEngineCtx *de_ctx, Signature *s, const char *unused)

{

    SigMatch *pm = NULL;

    int ret = -1;

    /* retrieve the sm to apply the depth against */

    pm = DetectGetLastSMFromLists(s, DETECT_CONTENT, -1);

    if (pm == NULL) {

        SCLogError("startswith needs a "

                   "preceding content option.");

        goto end;

    }

    /* verify other conditions. */

    DetectContentData *cd = (DetectContentData *)pm->ctx;

    if (cd->flags & DETECT_CONTENT_DEPTH) {

        SCLogError("can't use multiple "

                   "depth/startswith settings for the same content.");

        goto end;

    }

    if ((cd->flags & DETECT_CONTENT_WITHIN) || (cd->flags & DETECT_CONTENT_DISTANCE)) {

        SCLogError("can't use a relative "

                   "keyword like within/distance with a absolute "

                   "relative keyword like depth/offset for the same "

                   "content.");

        goto end;

    }

    if (cd->flags & DETECT_CONTENT_NEGATED && cd->flags & DETECT_CONTENT_FAST_PATTERN) {

        SCLogError("can't have a relative "

                   "negated keyword set along with a 'fast_pattern'.");

        goto end;

    }

    if (cd->flags & DETECT_CONTENT_FAST_PATTERN_ONLY) {

        SCLogError("can't have a relative "

                   "keyword set along with 'fast_pattern:only;'.");

        goto end;

    }

    if (cd->flags & DETECT_CONTENT_OFFSET) {

        SCLogError("can't mix offset "

                   "with startswith.");

        goto end;

    }

    cd->depth = cd->content_len;

    cd->flags |= DETECT_CONTENT_DEPTH;

    cd->flags |= DETECT_CONTENT_STARTS_WITH;

    ret = 0;

 end:

    return ret;

}