/* Copyright (C) 2007-2020 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>

 *

 */

#include "suricata-common.h"

#include "detect.h"

#include "detect-parse.h"

#include "detect-engine-prefilter-common.h"

#include "detect-engine-uint.h"

#include "util-byte.h"

#include "detect-tcpmss.h"

/* prototypes */

static int DetectTcpmssMatch (DetectEngineThreadCtx *, Packet *,

        const Signature *, const SigMatchCtx *);

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

void DetectTcpmssFree (DetectEngineCtx *, void *);

#ifdef UNITTESTS

void DetectTcpmssRegisterTests (void);

#endif

static int PrefilterSetupTcpmss(DetectEngineCtx *de_ctx, SigGroupHead *sgh);

static bool PrefilterTcpmssIsPrefilterable(const Signature *s);

/**

 * \brief Registration function for tcpmss: keyword

 */

void DetectTcpmssRegister(void)

{

    sigmatch_table[DETECT_TCPMSS].name = "tcp.mss";

    sigmatch_table[DETECT_TCPMSS].desc = "match on TCP MSS option field";

    sigmatch_table[DETECT_TCPMSS].url = "/rules/header-keywords.html#tcpmss";

    sigmatch_table[DETECT_TCPMSS].Match = DetectTcpmssMatch;

    sigmatch_table[DETECT_TCPMSS].Setup = DetectTcpmssSetup;

    sigmatch_table[DETECT_TCPMSS].Free = DetectTcpmssFree;

    sigmatch_table[DETECT_TCPMSS].SupportsPrefilter = PrefilterTcpmssIsPrefilterable;

    sigmatch_table[DETECT_TCPMSS].SetupPrefilter = PrefilterSetupTcpmss;

    return;

}

/**

 * \brief This function is used to match TCPMSS rule option on a packet with those passed via

 * tcpmss:

 *

 * \param det_ctx pointer to the pattern matcher thread

 * \param p pointer to the current packet

 * \param ctx pointer to the sigmatch that we will cast into DetectU16Data

 *

 * \retval 0 no match

 * \retval 1 match

 */

static int DetectTcpmssMatch (DetectEngineThreadCtx *det_ctx, Packet *p,

        const Signature *s, const SigMatchCtx *ctx)

{

    if (!(PKT_IS_TCP(p)) || PKT_IS_PSEUDOPKT(p))

        return 0;

    if (!(TCP_HAS_MSS(p)))

        return 0;

    uint16_t ptcpmss = TCP_GET_MSS(p);

    const DetectU16Data *tcpmssd = (const DetectU16Data *)ctx;

    return DetectU16Match(ptcpmss, tcpmssd);

}

/**

 * \brief this function is used to attach the parsed tcpmss data into the current signature

 *

 * \param de_ctx pointer to the Detection Engine Context

 * \param s pointer to the Current Signature

 * \param tcpmssstr pointer to the user provided tcpmss options

 *

 * \retval 0 on Success

 * \retval -1 on Failure

 */

static int DetectTcpmssSetup (DetectEngineCtx *de_ctx, Signature *s, const char *tcpmssstr)

{

    DetectU16Data *tcpmssd = DetectU16Parse(tcpmssstr);

    if (tcpmssd == NULL)

        return -1;

    SigMatch *sm = SigMatchAlloc();

    if (sm == NULL) {

        DetectTcpmssFree(de_ctx, tcpmssd);

        return -1;

    }

    sm->type = DETECT_TCPMSS;

    sm->ctx = (SigMatchCtx *)tcpmssd;

    SigMatchAppendSMToList(s, sm, DETECT_SM_LIST_MATCH);

    s->flags |= SIG_FLAG_REQUIRE_PACKET;

    return 0;

}

/**

 * \brief this function will free memory associated with DetectU16Data

 *

 * \param ptr pointer to DetectU16Data

 */

void DetectTcpmssFree(DetectEngineCtx *de_ctx, void *ptr)

{

    rs_detect_u16_free(ptr);

}

/* prefilter code */

static void

PrefilterPacketTcpmssMatch(DetectEngineThreadCtx *det_ctx, Packet *p, const void *pectx)

{

    if (!(PKT_IS_TCP(p)) || PKT_IS_PSEUDOPKT(p))

        return;

    if (!(TCP_HAS_MSS(p)))

        return;

    uint16_t ptcpmss = TCP_GET_MSS(p);

    /* during setup Suricata will automatically see if there is another

     * check that can be added: alproto, sport or dport */

    const PrefilterPacketHeaderCtx *ctx = pectx;

    if (!PrefilterPacketHeaderExtraMatch(ctx, p))

        return;

    DetectU16Data du16;

    du16.mode = ctx->v1.u8[0];

    du16.arg1 = ctx->v1.u16[1];

    du16.arg2 = ctx->v1.u16[2];

    /* if we match, add all the sigs that use this prefilter. This means

     * that these will be inspected further */

    if (DetectU16Match(ptcpmss, &du16)) {

        SCLogDebug("packet matches tcpmss/hl %u", ptcpmss);

        PrefilterAddSids(&det_ctx->pmq, ctx->sigs_array, ctx->sigs_cnt);

    }

}

static int PrefilterSetupTcpmss(DetectEngineCtx *de_ctx, SigGroupHead *sgh)

{

    return PrefilterSetupPacketHeader(de_ctx, sgh, DETECT_TCPMSS, PrefilterPacketU16Set,

            PrefilterPacketU16Compare, PrefilterPacketTcpmssMatch);

}

static bool PrefilterTcpmssIsPrefilterable(const Signature *s)

{

    const SigMatch *sm;

    for (sm = s->init_data->smlists[DETECT_SM_LIST_MATCH] ; sm != NULL; sm = sm->next) {

        switch (sm->type) {

            case DETECT_TCPMSS:

                return true;

        }

    }

    return false;

}