/* Copyright (C) 2007-2021 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.

 */

/**

 * \ingroup decode

 *

 * @{

 */

/**

 * \file

 *

 * \author Breno Silva <breno.silva@gmail.com>

 *

 * Decodes GRE

 */

#include "suricata-common.h"

#include "suricata.h"

#include "decode.h"

#include "decode-events.h"

#include "decode-gre.h"

#include "util-validate.h"

#include "util-unittest.h"

#include "util-debug.h"

/**

 * \brief Function to decode GRE packets

 */

int DecodeGRE(ThreadVars *tv, DecodeThreadVars *dtv, Packet *p, const uint8_t *pkt, uint32_t len)

{

    DEBUG_VALIDATE_BUG_ON(pkt == NULL);

    uint32_t header_len = GRE_HDR_LEN;

    GRESreHdr *gsre = NULL;

    GREPPtPHd *gre_pptp_h = NULL;

    StatsCounterIncr(&tv->stats, dtv->counter_gre);

    if(len < GRE_HDR_LEN)    {

        ENGINE_SET_INVALID_EVENT(p, GRE_PKT_TOO_SMALL);

        return TM_ECODE_FAILED;

    }

    if (!PacketIncreaseCheckLayers(p)) {

        return TM_ECODE_FAILED;

    }

    GREHdr *greh = PacketSetGRE(p, pkt);

    SCLogDebug("p %p pkt %p GRE protocol %04x Len: %d GRE version %x", p, pkt, GRE_GET_PROTO(greh),

            len, GRE_GET_VERSION(greh));

    switch (GRE_GET_VERSION(greh)) {

        case GRE_VERSION_0:

            /* GRE version 0 doesn't support the fields below RFC 1701 */

            /**

             * \todo We need to make sure this does not allow bypassing

             *       inspection.  A server may just ignore these and

             *       continue processing the packet, but we will not look

             *       further into it.

             */

            if (GRE_FLAG_ISSET_RECUR(greh)) {

                ENGINE_SET_INVALID_EVENT(p, GRE_VERSION0_RECUR);

                return TM_ECODE_OK;

            }

            if (GREV1_FLAG_ISSET_FLAGS(greh)) {

                ENGINE_SET_INVALID_EVENT(p, GRE_VERSION0_FLAGS);

                return TM_ECODE_OK;

            }

            /* Adjust header length based on content */

            if (GRE_FLAG_ISSET_KY(greh))

                header_len += GRE_KEY_LEN;

            if (GRE_FLAG_ISSET_SQ(greh))

                header_len += GRE_SEQ_LEN;

            if (GRE_FLAG_ISSET_CHKSUM(greh) || GRE_FLAG_ISSET_ROUTE(greh))

                header_len += GRE_CHKSUM_LEN + GRE_OFFSET_LEN;

            if (header_len > len)   {

                ENGINE_SET_INVALID_EVENT(p, GRE_VERSION0_HDR_TOO_BIG);

                return TM_ECODE_OK;

            }

            if (GRE_FLAG_ISSET_ROUTE(greh)) {

                while (1)

                {

                    if ((header_len + GRE_SRE_HDR_LEN) > len) {

                        ENGINE_SET_INVALID_EVENT(p,

                                                 GRE_VERSION0_MALFORMED_SRE_HDR);

                        return TM_ECODE_OK;

                    }

                    gsre = (GRESreHdr *)(pkt + header_len);

                    header_len += GRE_SRE_HDR_LEN;

                    if ((SCNtohs(gsre->af) == 0) && (gsre->sre_length == 0))

                        break;

                    header_len += gsre->sre_length;

                    if (header_len > len) {

                        ENGINE_SET_INVALID_EVENT(p,

                                                 GRE_VERSION0_MALFORMED_SRE_HDR);

                        return TM_ECODE_OK;

                    }

                }

            }

            break;

        case GRE_VERSION_1:

            /* GRE version 1 doesn't support the fields below RFC 1701 */

            /**

             * \todo We need to make sure this does not allow bypassing

             *       inspection.  A server may just ignore these and

             *       continue processing the packet, but we will not look

             *       further into it.

             */

            if (GRE_FLAG_ISSET_CHKSUM(greh)) {

                ENGINE_SET_INVALID_EVENT(p,GRE_VERSION1_CHKSUM);

                return TM_ECODE_OK;

            }

            if (GRE_FLAG_ISSET_ROUTE(greh)) {

                ENGINE_SET_INVALID_EVENT(p,GRE_VERSION1_ROUTE);

                return TM_ECODE_OK;

            }

            if (GRE_FLAG_ISSET_SSR(greh)) {

                ENGINE_SET_INVALID_EVENT(p,GRE_VERSION1_SSR);

                return TM_ECODE_OK;

            }

            if (GRE_FLAG_ISSET_RECUR(greh)) {

                ENGINE_SET_INVALID_EVENT(p,GRE_VERSION1_RECUR);

                return TM_ECODE_OK;

            }

            if (GREV1_FLAG_ISSET_FLAGS(greh)) {

                ENGINE_SET_INVALID_EVENT(p,GRE_VERSION1_FLAGS);

                return TM_ECODE_OK;

            }

            if (GRE_GET_PROTO(greh) != GRE_PROTO_PPP) {

                ENGINE_SET_INVALID_EVENT(p,GRE_VERSION1_WRONG_PROTOCOL);

                return TM_ECODE_OK;

            }

            if (!(GRE_FLAG_ISSET_KY(greh))) {

                ENGINE_SET_INVALID_EVENT(p,GRE_VERSION1_NO_KEY);

                return TM_ECODE_OK;

            }

            header_len += GRE_KEY_LEN;

            /* key is set and proto == PPP */

            gre_pptp_h = (GREPPtPHd *)pkt;

            /* Adjust header length based on content */

            if (GRE_FLAG_ISSET_SQ(greh))

                header_len += GRE_SEQ_LEN;

            if (GREV1_FLAG_ISSET_ACK(greh))

                header_len += GREV1_ACK_LEN;

            if (header_len > len)   {

                ENGINE_SET_INVALID_EVENT(p, GRE_VERSION1_HDR_TOO_BIG);

                return TM_ECODE_OK;

            }

            break;

        default:

            ENGINE_SET_INVALID_EVENT(p, GRE_WRONG_VERSION);

            return TM_ECODE_OK;

    }

    switch (GRE_GET_PROTO(greh)) {

        case ETHERNET_TYPE_IP:

        {

            Packet *tp = PacketTunnelPktSetup(tv, dtv, p, pkt + header_len,

                    len - header_len, DECODE_TUNNEL_IPV4);

            if (tp != NULL) {

                PKT_SET_SRC(tp, PKT_SRC_DECODER_GRE);

                PacketEnqueueNoLock(&tv->decode_pq,tp);

            }

            break;

        }

        case GRE_PROTO_PPP:

        {

            if (gre_pptp_h && !gre_pptp_h->payload_length)

                return TM_ECODE_OK;

            Packet *tp = PacketTunnelPktSetup(tv, dtv, p, pkt + header_len,

                    len - header_len, DECODE_TUNNEL_PPP);

            if (tp != NULL) {

                PKT_SET_SRC(tp, PKT_SRC_DECODER_GRE);

                PacketEnqueueNoLock(&tv->decode_pq,tp);

            }

            break;

        }

        case ETHERNET_TYPE_IPV6:

        {

            Packet *tp = PacketTunnelPktSetup(tv, dtv, p, pkt + header_len,

                    len - header_len, DECODE_TUNNEL_IPV6);

            if (tp != NULL) {

                PKT_SET_SRC(tp, PKT_SRC_DECODER_GRE);

                PacketEnqueueNoLock(&tv->decode_pq,tp);

            }

            break;

        }

        case ETHERNET_TYPE_VLAN:

        {

            Packet *tp = PacketTunnelPktSetup(tv, dtv, p, pkt + header_len,

                    len - header_len, DECODE_TUNNEL_VLAN);

            if (tp != NULL) {

                PKT_SET_SRC(tp, PKT_SRC_DECODER_GRE);

                PacketEnqueueNoLock(&tv->decode_pq,tp);

            }

            break;

        }

        case ETHERNET_TYPE_ERSPAN:

        {

            // Determine if it's Type I or Type II based on the flags in the GRE header.

            // Type I:  0|0|0|0|0|00000|000000000|00000

            // Type II: 0|0|0|1|0|00000|000000000|00000

            //                Seq

            Packet *tp = PacketTunnelPktSetup(tv, dtv, p, pkt + header_len, len - header_len,

                    GRE_FLAG_ISSET_SQ(greh) == 0 ? DECODE_TUNNEL_ERSPANI : DECODE_TUNNEL_ERSPANII);

            if (tp != NULL) {

                PKT_SET_SRC(tp, PKT_SRC_DECODER_GRE);

                PacketEnqueueNoLock(&tv->decode_pq,tp);

            }

            break;

        }

        case ETHERNET_TYPE_BRIDGE:

        {

            Packet *tp = PacketTunnelPktSetup(tv, dtv, p, pkt + header_len,

                    len - header_len, DECODE_TUNNEL_ETHERNET);

            if (tp != NULL) {

                PKT_SET_SRC(tp, PKT_SRC_DECODER_GRE);

                PacketEnqueueNoLock(&tv->decode_pq,tp);

            }

            break;

        }

        case ETHERNET_TYPE_ARP: {

            Packet *tp = PacketTunnelPktSetup(

                    tv, dtv, p, pkt + header_len, len - header_len, DECODE_TUNNEL_ARP);

            if (tp != NULL) {

                PKT_SET_SRC(tp, PKT_SRC_DECODER_GRE);

                PacketEnqueueNoLock(&tv->decode_pq, tp);

            }

            break;

        }

        default:

            return TM_ECODE_OK;

    }

    return TM_ECODE_OK;

}

#ifdef UNITTESTS

/**

 * \test DecodeGRETest01 is a test for small gre packet

 */

static int DecodeGREtest01 (void)

{

    uint8_t raw_gre[] = { 0x00 ,0x6e ,0x62 };

    Packet *p = PacketGetFromAlloc();

    FAIL_IF_NULL(p);

    ThreadVars tv;

    DecodeThreadVars dtv;

    memset(&tv, 0, sizeof(ThreadVars));

    memset(&dtv, 0, sizeof(DecodeThreadVars));

    DecodeGRE(&tv, &dtv, p, raw_gre, sizeof(raw_gre));

    FAIL_IF_NOT(ENGINE_ISSET_EVENT(p, GRE_PKT_TOO_SMALL));

    PacketFree(p);

    PASS;

}

/**

 * \test DecodeGRETest02 is a test for wrong gre version

 */

static int DecodeGREtest02 (void)

{

    uint8_t raw_gre[] = {

        0x00, 0x6e, 0x62, 0xac, 0x40, 0x00, 0x40, 0x2f,

        0xc2, 0xc7, 0x0a, 0x00, 0x00, 0x64, 0x0a, 0x00,

        0x00, 0x8a, 0x30, 0x01, 0x0b, 0x00, 0x4e, 0x00,

        0x00, 0x00, 0x18, 0x4a, 0x50, 0xff, 0x03, 0x00,

        0x21, 0x45, 0x00, 0x00, 0x4a, 0x00, 0x00, 0x40,

        0x00, 0x40, 0x11, 0x94, 0x22, 0x50, 0x7e, 0x2b,

        0x2d, 0xc2, 0x6d, 0x68, 0x68, 0x80, 0x0e, 0x00,

        0x35, 0x00, 0x36, 0x9f, 0x18, 0xdb, 0xc4, 0x01,

        0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,

        0x01, 0x03, 0x73, 0x31, 0x36, 0x09, 0x73, 0x69,

        0x74, 0x65, 0x6d, 0x65, 0x74, 0x65, 0x72, 0x03,

        0x63, 0x6f, 0x6d, 0x00, 0x00, 0x01, 0x00, 0x01,

        0x00, 0x00, 0x29, 0x10, 0x00, 0x00, 0x00, 0x00,

        0x00, 0x00, 0x00 };

    Packet *p = PacketGetFromAlloc();

    FAIL_IF_NULL(p);

    ThreadVars tv;

    DecodeThreadVars dtv;

    memset(&tv, 0, sizeof(ThreadVars));

    memset(&dtv, 0, sizeof(DecodeThreadVars));

    DecodeGRE(&tv, &dtv, p, raw_gre, sizeof(raw_gre));

    FAIL_IF_NOT(ENGINE_ISSET_EVENT(p, GRE_WRONG_VERSION));

    PacketFree(p);

    PASS;

}

/**

 * \test DecodeGRETest03 is a test for valid gre packet

 */

static int DecodeGREtest03 (void)

{

    uint8_t raw_gre[] = {

        0x00, 0x6e, 0x62, 0xac, 0x40, 0x00, 0x40, 0x2f,

        0xc2, 0xc7, 0x0a, 0x00, 0x00, 0x64, 0x0a, 0x00,

        0x00, 0x8a, 0x30, 0x01, 0x88, 0x0b, 0x00, 0x4e,

        0x00, 0x00, 0x00, 0x18, 0x4a, 0x50, 0xff, 0x03,

        0x00, 0x21, 0x45, 0x00, 0x00, 0x4a, 0x00, 0x00,

        0x40, 0x00, 0x40, 0x11, 0x94, 0x22, 0x50, 0x7e,

        0x2b, 0x2d, 0xc2, 0x6d, 0x68, 0x68, 0x80, 0x0e,

        0x00, 0x35, 0x00, 0x36, 0x9f, 0x18, 0xdb, 0xc4,

        0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,

        0x00, 0x01, 0x03, 0x73, 0x31, 0x36, 0x09, 0x73,

        0x69, 0x74, 0x65, 0x6d, 0x65, 0x74, 0x65, 0x72,

        0x03, 0x63, 0x6f, 0x6d, 0x00, 0x00, 0x01, 0x00,

        0x01, 0x00, 0x00, 0x29, 0x10, 0x00, 0x00, 0x00,

        0x00, 0x00, 0x00, 0x00 };

    Packet *p = PacketGetFromAlloc();

    FAIL_IF_NULL(p);

    ThreadVars tv;

    DecodeThreadVars dtv;

    memset(&tv, 0, sizeof(ThreadVars));

    memset(&dtv, 0, sizeof(DecodeThreadVars));

    DecodeGRE(&tv, &dtv, p, raw_gre, sizeof(raw_gre));

    FAIL_IF_NOT(PacketIsGRE(p));

    PacketFree(p);

    PASS;

}

#endif /* UNITTESTS */

/**

 * \brief this function registers unit tests for GRE decoder

 */

void DecodeGRERegisterTests(void)

{

#ifdef UNITTESTS

    UtRegisterTest("DecodeGREtest01", DecodeGREtest01);

    UtRegisterTest("DecodeGREtest02", DecodeGREtest02);

    UtRegisterTest("DecodeGREtest03", DecodeGREtest03);

#endif /* UNITTESTS */

}

/**

 * @}

 */