/* Copyright (C) 2017-2022 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 Mats Klepsland <mats.klepsland@gmail.com>

 *

 * Implements support for tls_cert_fingerprint keyword.

 */

#include "suricata-common.h"

#include "threads.h"

#include "decode.h"

#include "detect.h"

#include "detect-parse.h"

#include "detect-engine.h"

#include "detect-engine-mpm.h"

#include "detect-engine-prefilter.h"

#include "detect-content.h"

#include "detect-pcre.h"

#include "detect-tls-cert-fingerprint.h"

#include "flow.h"

#include "flow-util.h"

#include "flow-var.h"

#include "util-debug.h"

#include "util-spm.h"

#include "util-print.h"

#include "stream-tcp.h"

#include "app-layer.h"

#include "app-layer-ssl.h"

#include "util-unittest.h"

#include "util-unittest-helper.h"

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

#ifdef UNITTESTS

static void DetectTlsFingerprintRegisterTests(void);

#endif

static InspectionBuffer *GetData(DetectEngineThreadCtx *det_ctx,

        const DetectEngineTransforms *transforms,

        Flow *f, const uint8_t flow_flags,

        void *txv, const int list_id);

static void DetectTlsFingerprintSetupCallback(const DetectEngineCtx *de_ctx,

        Signature *s);

static bool DetectTlsFingerprintValidateCallback(const Signature *s,

        const char **sigerror);

static int g_tls_cert_fingerprint_buffer_id = 0;

/**

 * \brief Registration function for keyword: tls.cert_fingerprint

 */

void DetectTlsFingerprintRegister(void)

{

    sigmatch_table[DETECT_AL_TLS_CERT_FINGERPRINT].name = "tls.cert_fingerprint";

    sigmatch_table[DETECT_AL_TLS_CERT_FINGERPRINT].alias = "tls_cert_fingerprint";

    sigmatch_table[DETECT_AL_TLS_CERT_FINGERPRINT].desc =

            "sticky buffer to match the TLS cert fingerprint buffer";

    sigmatch_table[DETECT_AL_TLS_CERT_FINGERPRINT].url = "/rules/tls-keywords.html#tls-cert-fingerprint";

    sigmatch_table[DETECT_AL_TLS_CERT_FINGERPRINT].Setup = DetectTlsFingerprintSetup;

#ifdef UNITTESTS

    sigmatch_table[DETECT_AL_TLS_CERT_FINGERPRINT].RegisterTests = DetectTlsFingerprintRegisterTests;

#endif

    sigmatch_table[DETECT_AL_TLS_CERT_FINGERPRINT].flags |= SIGMATCH_NOOPT;

    sigmatch_table[DETECT_AL_TLS_CERT_FINGERPRINT].flags |= SIGMATCH_INFO_STICKY_BUFFER;

    DetectAppLayerInspectEngineRegister2("tls.cert_fingerprint", ALPROTO_TLS,

            SIG_FLAG_TOCLIENT, TLS_STATE_CERT_READY,

            DetectEngineInspectBufferGeneric, GetData);

    DetectAppLayerMpmRegister2("tls.cert_fingerprint", SIG_FLAG_TOCLIENT, 2,

            PrefilterGenericMpmRegister, GetData, ALPROTO_TLS,

            TLS_STATE_CERT_READY);

    DetectAppLayerInspectEngineRegister2("tls.cert_fingerprint", ALPROTO_TLS, SIG_FLAG_TOSERVER,

            TLS_STATE_CERT_READY, DetectEngineInspectBufferGeneric, GetData);

    DetectAppLayerMpmRegister2("tls.cert_fingerprint", SIG_FLAG_TOSERVER, 2,

            PrefilterGenericMpmRegister, GetData, ALPROTO_TLS, TLS_STATE_CERT_READY);

    DetectBufferTypeSetDescriptionByName("tls.cert_fingerprint",

            "TLS certificate fingerprint");

    DetectBufferTypeRegisterSetupCallback("tls.cert_fingerprint",

            DetectTlsFingerprintSetupCallback);

    DetectBufferTypeRegisterValidateCallback("tls.cert_fingerprint",

            DetectTlsFingerprintValidateCallback);

    g_tls_cert_fingerprint_buffer_id = DetectBufferTypeGetByName("tls.cert_fingerprint");

}

/**

 * \brief this function setup the tls_cert_fingerprint modifier keyword used in the rule

 *

 * \param de_ctx   Pointer to the Detection Engine Context

 * \param s        Pointer to the Signature to which the current keyword belongs

 * \param str      Should hold an empty string always

 *

 * \retval 0  On success

 * \retval -1 On failure

 */

static int DetectTlsFingerprintSetup(DetectEngineCtx *de_ctx, Signature *s,

                                     const char *str)

{

    if (DetectBufferSetActiveList(de_ctx, s, g_tls_cert_fingerprint_buffer_id) < 0)

        return -1;

    if (DetectSignatureSetAppProto(s, ALPROTO_TLS) < 0)

        return -1;

    return 0;

}

static InspectionBuffer *GetData(DetectEngineThreadCtx *det_ctx,

        const DetectEngineTransforms *transforms, Flow *f,

        const uint8_t flow_flags, void *txv, const int list_id)

{

    InspectionBuffer *buffer = InspectionBufferGet(det_ctx, list_id);

    if (buffer->inspect == NULL) {

        const SSLState *ssl_state = (SSLState *)f->alstate;

        const SSLStateConnp *connp;

        if (flow_flags & STREAM_TOSERVER) {

            connp = &ssl_state->client_connp;

        } else {

            connp = &ssl_state->server_connp;

        }

        if (connp->cert0_fingerprint == NULL) {

            return NULL;

        }

        const uint32_t data_len = strlen(connp->cert0_fingerprint);

        const uint8_t *data = (uint8_t *)connp->cert0_fingerprint;

        InspectionBufferSetup(det_ctx, list_id, buffer, data, data_len);

        InspectionBufferApplyTransforms(buffer, transforms);

    }

    return buffer;

}

static bool DetectTlsFingerprintValidateCallback(const Signature *s,

                                                  const char **sigerror)

{

    for (uint32_t x = 0; x < s->init_data->buffer_index; x++) {

        if (s->init_data->buffers[x].id != (uint32_t)g_tls_cert_fingerprint_buffer_id)

            continue;

        const SigMatch *sm = s->init_data->buffers[x].head;

        for (; sm != NULL; sm = sm->next) {

            if (sm->type != DETECT_CONTENT)

                continue;

            const DetectContentData *cd = (DetectContentData *)sm->ctx;

            if (cd->content_len != 59) {

                *sigerror = "Invalid length of the specified fingerprint. "

                            "This rule will therefore never match.";

                SCLogWarning("rule %u: %s", s->id, *sigerror);

                return false;

            }

            bool have_delimiters = false;

            uint32_t u;

            for (u = 0; u < cd->content_len; u++) {

                if (cd->content[u] == ':') {

                    have_delimiters = true;

                    break;

                }

            }

            if (!have_delimiters) {

                *sigerror = "No colon delimiters ':' detected in content after "

                            "tls.cert_fingerprint. This rule will therefore "

                            "never match.";

                SCLogWarning("rule %u: %s", s->id, *sigerror);

                return false;

            }

            if (cd->flags & DETECT_CONTENT_NOCASE) {

                *sigerror = "tls.cert_fingerprint should not be used together "

                            "with nocase, since the rule is automatically "

                            "lowercased anyway which makes nocase redundant.";

                SCLogWarning("rule %u: %s", s->id, *sigerror);

            }

        }

    }

    return true;

}

static void DetectTlsFingerprintSetupCallback(const DetectEngineCtx *de_ctx,

                                              Signature *s)

{

    for (uint32_t x = 0; x < s->init_data->buffer_index; x++) {

        if (s->init_data->buffers[x].id != (uint32_t)g_tls_cert_fingerprint_buffer_id)

            continue;

        SigMatch *sm = s->init_data->buffers[x].head;

        for (; sm != NULL; sm = sm->next) {

            if (sm->type != DETECT_CONTENT)

                continue;

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

            bool changed = false;

            uint32_t u;

            for (u = 0; u < cd->content_len; u++) {

                if (isupper(cd->content[u])) {

                    cd->content[u] = u8_tolower(cd->content[u]);

                    changed = true;

                }

            }

            /* recreate the context if changes were made */

            if (changed) {

                SpmDestroyCtx(cd->spm_ctx);

                cd->spm_ctx =

                        SpmInitCtx(cd->content, cd->content_len, 1, de_ctx->spm_global_thread_ctx);

            }

        }

    }

}

#ifdef UNITTESTS

#include "detect-engine-alert.h"

#include "tests/detect-tls-cert-fingerprint.c"

#endif