/* 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.

 */

/**

 * \file

 *

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

 *

 * Implements fragoffset keyword

 */

#include "suricata-common.h"

#include "decode.h"

#include "decode-ipv4.h"

#include "decode-ipv6.h"

#include "detect.h"

#include "detect-parse.h"

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

#include "detect-engine-build.h"

#include "detect-fragoffset.h"

#include "util-byte.h"

#include "util-unittest.h"

#include "util-debug.h"

#define PARSE_REGEX "^\\s*(?:(<|>))?\\s*([0-9]+)"

static DetectParseRegex parse_regex;

static int DetectFragOffsetMatch(DetectEngineThreadCtx *,

        Packet *, const Signature *, const SigMatchCtx *);

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

#ifdef UNITTESTS

void DetectFragOffsetRegisterTests(void);

#endif

void DetectFragOffsetFree(DetectEngineCtx *, void *);

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

static bool PrefilterFragOffsetIsPrefilterable(const Signature *s);

/**

 * \brief Registration function for fragoffset

 */

void DetectFragOffsetRegister (void)

{

    sigmatch_table[DETECT_FRAGOFFSET].name = "fragoffset";

    sigmatch_table[DETECT_FRAGOFFSET].desc = "match on specific decimal values of the IP fragment offset field";

    sigmatch_table[DETECT_FRAGOFFSET].url = "/rules/header-keywords.html#fragoffset";

    sigmatch_table[DETECT_FRAGOFFSET].Match = DetectFragOffsetMatch;

    sigmatch_table[DETECT_FRAGOFFSET].Setup = DetectFragOffsetSetup;

    sigmatch_table[DETECT_FRAGOFFSET].Free = DetectFragOffsetFree;

#ifdef UNITTESTS

    sigmatch_table[DETECT_FRAGOFFSET].RegisterTests = DetectFragOffsetRegisterTests;

#endif

    sigmatch_table[DETECT_FRAGOFFSET].SupportsPrefilter = PrefilterFragOffsetIsPrefilterable;

    sigmatch_table[DETECT_FRAGOFFSET].SetupPrefilter = PrefilterSetupFragOffset;

    DetectSetupParseRegexes(PARSE_REGEX, &parse_regex);

}

static inline int FragOffsetMatch(const uint16_t poffset, const uint8_t mode,

                                  const uint16_t doffset)

{

    switch (mode)  {

        case FRAG_LESS:

            if (poffset < doffset)

                return 1;

            break;

        case FRAG_MORE:

            if (poffset > doffset)

                return 1;

            break;

        default:

            if (poffset == doffset)

                return 1;

    }

    return 0;

}

/**

 * \brief This function is used to match fragoffset rule option set on a packet

 *

 * \param t pointer to thread vars

 * \param det_ctx pointer to the pattern matcher thread

 * \param p pointer to the current packet

 * \param m pointer to the sigmatch that we will cast into DetectFragOffsetData

 *

 * \retval 0 no match or frag is not set

 * \retval 1 match

 *

 */

static int DetectFragOffsetMatch (DetectEngineThreadCtx *det_ctx,

        Packet *p, const Signature *s, const SigMatchCtx *ctx)

{

    uint16_t frag = 0;

    const DetectFragOffsetData *fragoff = (const DetectFragOffsetData *)ctx;

    if (PKT_IS_PSEUDOPKT(p))

        return 0;

    if (PKT_IS_IPV4(p)) {

        frag = IPV4_GET_IPOFFSET(p);

    } else if (PKT_IS_IPV6(p)) {

        if (IPV6_EXTHDR_ISSET_FH(p)) {

            frag = IPV6_EXTHDR_GET_FH_OFFSET(p);

        } else {

            return 0;

        }

    } else {

        SCLogDebug("No IPv4 or IPv6 packet");

        return 0;

    }

    return FragOffsetMatch(frag, fragoff->mode, fragoff->frag_off);

}

/**

 * \brief This function is used to parse fragoffset option passed via fragoffset: keyword

 *

 * \param de_ctx Pointer to the detection engine context

 * \param fragoffsetstr Pointer to the user provided fragoffset options

 *

 * \retval fragoff pointer to DetectFragOffsetData on success

 * \retval NULL on failure

 */

static DetectFragOffsetData *DetectFragOffsetParse (DetectEngineCtx *de_ctx, const char *fragoffsetstr)

{

    DetectFragOffsetData *fragoff = NULL;

    char *substr[3] = {NULL, NULL, NULL};

    int res = 0;

    size_t pcre2_len;

    int i;

    const char *str_ptr;

    char *mode = NULL;

    pcre2_match_data *match = NULL;

    int ret = DetectParsePcreExec(&parse_regex, &match, fragoffsetstr, 0, 0);

    if (ret < 1 || ret > 4) {

        SCLogError("Parse error %s", fragoffsetstr);

        goto error;

    }

    for (i = 1; i < ret; i++) {

        res = SC_Pcre2SubstringGet(match, i, (PCRE2_UCHAR8 **)&str_ptr, &pcre2_len);

        if (res < 0) {

            SCLogError("pcre2_substring_get_bynumber failed");

            goto error;

        }

        substr[i-1] = (char *)str_ptr;

    }

    fragoff = SCMalloc(sizeof(DetectFragOffsetData));

    if (unlikely(fragoff == NULL))

        goto error;

    fragoff->frag_off = 0;

    fragoff->mode = 0;

    mode = substr[0];

    if(mode != NULL)    {

        while(*mode != '\0')    {

            switch(*mode)   {

                case '>':

                    fragoff->mode = FRAG_MORE;

                    break;

                case '<':

                    fragoff->mode = FRAG_LESS;

                    break;

            }

            mode++;

        }

    }

    if (StringParseUint16(&fragoff->frag_off, 10, 0, substr[1]) < 0) {

        SCLogError("specified frag offset %s is not "

                   "valid",

                substr[1]);

        goto error;

    }

    for (i = 0; i < 3; i++) {

        if (substr[i] != NULL)

            pcre2_substring_free((PCRE2_UCHAR8 *)substr[i]);

    }

    pcre2_match_data_free(match);

    return fragoff;

error:

    if (match) {

        pcre2_match_data_free(match);

    }

    for (i = 0; i < 3; i++) {

        if (substr[i] != NULL)

            pcre2_substring_free((PCRE2_UCHAR8 *)substr[i]);

    }

    if (fragoff != NULL) DetectFragOffsetFree(de_ctx, fragoff);

    return NULL;

}

/**

 * \brief this function is used to add the parsed fragoffset data into the current signature

 *

 * \param de_ctx pointer to the Detection Engine Context

 * \param s pointer to the Current Signature

 * \param fragoffsetstr pointer to the user provided fragoffset option

 *

 * \retval 0 on Success

 * \retval -1 on Failure

 */

static int DetectFragOffsetSetup (DetectEngineCtx *de_ctx, Signature *s, const char *fragoffsetstr)

{

    DetectFragOffsetData *fragoff = NULL;

    SigMatch *sm = NULL;

    fragoff = DetectFragOffsetParse(de_ctx, fragoffsetstr);

    if (fragoff == NULL) goto error;

    sm = SigMatchAlloc();

    if (sm == NULL) goto error;

    sm->type = DETECT_FRAGOFFSET;

    sm->ctx = (SigMatchCtx *)fragoff;

    SigMatchAppendSMToList(s, sm, DETECT_SM_LIST_MATCH);

    s->flags |= SIG_FLAG_REQUIRE_PACKET;

    return 0;

error:

    if (fragoff != NULL) DetectFragOffsetFree(de_ctx, fragoff);

    if (sm != NULL) SCFree(sm);

    return -1;

}

/**

 * \brief this function will free memory associated with DetectFragOffsetData

 *

 * \param ptr pointer to DetectFragOffsetData

 */

void DetectFragOffsetFree (DetectEngineCtx *de_ctx, void *ptr)

{

    DetectFragOffsetData *fragoff = (DetectFragOffsetData *)ptr;

    SCFree(fragoff);

}

static void

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

{

    if (PKT_IS_PSEUDOPKT(p))

        return;

    uint16_t frag;

    if (PKT_IS_IPV4(p)) {

        frag = IPV4_GET_IPOFFSET(p);

    } else if (PKT_IS_IPV6(p)) {

        if (IPV6_EXTHDR_ISSET_FH(p)) {

            frag = IPV6_EXTHDR_GET_FH_OFFSET(p);

        } else {

            return;

        }

    } else {

        SCLogDebug("No IPv4 or IPv6 packet");

        return;

    }

    const PrefilterPacketHeaderCtx *ctx = pectx;

    if (FragOffsetMatch(frag, ctx->v1.u8[0], ctx->v1.u16[1]))

    {

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

    }

}

static void

PrefilterPacketFragOffsetSet(PrefilterPacketHeaderValue *v, void *smctx)

{

    const DetectFragOffsetData *fb = smctx;

    v->u8[0] = fb->mode;

    v->u16[1] = fb->frag_off;

}

static bool

PrefilterPacketFragOffsetCompare(PrefilterPacketHeaderValue v, void *smctx)

{

    const DetectFragOffsetData *fb = smctx;

    if (v.u8[0] == fb->mode &&

        v.u16[1] == fb->frag_off)

    {

        return true;

    }

    return false;

}

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

{

    return PrefilterSetupPacketHeader(de_ctx, sgh, DETECT_FRAGOFFSET,

        PrefilterPacketFragOffsetSet,

        PrefilterPacketFragOffsetCompare,

        PrefilterPacketFragOffsetMatch);

}

static bool PrefilterFragOffsetIsPrefilterable(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_FRAGOFFSET:

                return true;

        }

    }

    return false;

}

#ifdef UNITTESTS

#include "util-unittest-helper.h"

#include "detect-engine.h"

#include "detect-engine-alert.h"

/**

 * \test DetectFragOffsetParseTest01 is a test for setting a valid fragoffset value

 */

static int DetectFragOffsetParseTest01 (void)

{

    DetectFragOffsetData *fragoff = DetectFragOffsetParse(NULL, "300");

    FAIL_IF_NULL(fragoff);

    FAIL_IF_NOT(fragoff->frag_off == 300);

    DetectFragOffsetFree(NULL, fragoff);

    PASS;

}

/**

 * \test DetectFragOffsetParseTest02 is a test for setting a valid fragoffset value

 *       with spaces all around

 */

static int DetectFragOffsetParseTest02 (void)

{

    DetectFragOffsetData *fragoff = DetectFragOffsetParse(NULL, ">300");

    FAIL_IF_NULL(fragoff);

    FAIL_IF_NOT(fragoff->frag_off == 300);

    FAIL_IF_NOT(fragoff->mode == FRAG_MORE);

    DetectFragOffsetFree(NULL, fragoff);

    PASS;

}

/**

 * \test DetectFragOffsetParseTest03 is a test for setting an invalid fragoffset value

 */

static int DetectFragOffsetParseTest03 (void)

{

    DetectFragOffsetData *fragoff = DetectFragOffsetParse(NULL, "badc");

    FAIL_IF_NOT_NULL(fragoff);

    PASS;

}

/**

 * \test DetectFragOffsetMatchTest01 is a test for checking the working of

 *       fragoffset keyword by creating 2 rules and matching a crafted packet

 *       against them. Only the first one shall trigger.

 */

static int DetectFragOffsetMatchTest01 (void)

{

    Packet *p = PacketGetFromAlloc();

    FAIL_IF_NULL(p);

    Signature *s = NULL;

    DecodeThreadVars dtv;

    ThreadVars th_v;

    DetectEngineThreadCtx *det_ctx = NULL;

    IPV4Hdr ip4h;

    memset(&ip4h, 0, sizeof(IPV4Hdr));

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

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

    FlowInitConfig(FLOW_QUIET);

    p->src.family = AF_INET;

    p->dst.family = AF_INET;

    p->src.addr_data32[0] = 0x01020304;

    p->dst.addr_data32[0] = 0x04030201;

    ip4h.s_ip_src.s_addr = p->src.addr_data32[0];

    ip4h.s_ip_dst.s_addr = p->dst.addr_data32[0];

    ip4h.ip_off = 0x2222;

    p->ip4h = &ip4h;

    DetectEngineCtx *de_ctx = DetectEngineCtxInit();

    FAIL_IF_NULL(de_ctx);

    de_ctx->flags |= DE_QUIET;

    s = DetectEngineAppendSig(de_ctx, "alert ip any any -> any any (fragoffset:546; sid:1;)");

    FAIL_IF_NULL(s);

    s = DetectEngineAppendSig(de_ctx, "alert ip any any -> any any (fragoffset:5000; sid:2;)");

    FAIL_IF_NULL(s);

    SigGroupBuild(de_ctx);

    DetectEngineThreadCtxInit(&th_v, (void *)de_ctx, (void *)&det_ctx);

    SigMatchSignatures(&th_v, de_ctx, det_ctx, p);

    FAIL_IF(PacketAlertCheck(p, 1) == 0);

    FAIL_IF(PacketAlertCheck(p, 2));

    DetectEngineThreadCtxDeinit(&th_v, (void *)det_ctx);

    DetectEngineCtxFree(de_ctx);

    FlowShutdown();

    SCFree(p);

    PASS;

}

void DetectFragOffsetRegisterTests (void)

{

    UtRegisterTest("DetectFragOffsetParseTest01", DetectFragOffsetParseTest01);

    UtRegisterTest("DetectFragOffsetParseTest02", DetectFragOffsetParseTest02);

    UtRegisterTest("DetectFragOffsetParseTest03", DetectFragOffsetParseTest03);

    UtRegisterTest("DetectFragOffsetMatchTest01", DetectFragOffsetMatchTest01);

}

#endif /* UNITTESTS */