/* 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 Vadym Malakhatko <v.malakhatko@sirinsoftware.com>

 */

#include "suricata-common.h"

#include "threads.h"

#include "decode.h"

#include "detect.h"

#include "detect-parse.h"

#include "detect-content.h"

#include "detect-engine.h"

#include "detect-engine-mpm.h"

#include "detect-engine-state.h"

#include "detect-engine-prefilter.h"

#include "flow.h"

#include "flow-var.h"

#include "flow-util.h"

#include "stream-tcp.h"

#include "util-debug.h"

#include "util-unittest.h"

#include "util-unittest-helper.h"

#include "app-layer.h"

#include "app-layer-parser.h"

#include "app-layer-ssh.h"

#include "detect-ssh-hassh-server.h"

#include "rust.h"

#define KEYWORD_NAME "ssh.hassh.server"

#define KEYWORD_ALIAS "ssh-hassh-server"

#define KEYWORD_DOC "ssh-keywords.html#ssh.hassh.server"

#define BUFFER_NAME "ssh.hassh.server"

#define BUFFER_DESC "Ssh Client Fingerprinting For Ssh Servers"

static int g_ssh_hassh_buffer_id = 0;

static InspectionBuffer *GetSshData(DetectEngineThreadCtx *det_ctx,

        const DetectEngineTransforms *transforms, Flow *_f,

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

{

    SCEnter();

    InspectionBuffer *buffer = InspectionBufferGet(det_ctx, list_id);

    if (buffer->inspect == NULL) {

        const uint8_t *hasshServer = NULL;

        uint32_t b_len = 0;

        if (rs_ssh_tx_get_hassh(txv, &hasshServer, &b_len, flow_flags) != 1)

            return NULL;

        if (hasshServer == NULL || b_len == 0) {

            SCLogDebug("SSH hassh not set");

            return NULL;

        }

        InspectionBufferSetup(det_ctx, list_id, buffer, hasshServer, b_len);

        InspectionBufferApplyTransforms(buffer, transforms);

    }

    return buffer;

}

/**

 * \brief this function setup the ssh.hassh.server 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

 * \retval -2 on failure that should be silent after the first

 */

static int DetectSshHasshServerSetup(DetectEngineCtx *de_ctx, Signature *s, const char *arg)

{

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

        return -1;

    if (DetectSignatureSetAppProto(s, ALPROTO_SSH) < 0)

        return -1;

    /* try to enable Hassh */

    rs_ssh_enable_hassh();

    /* Check if Hassh is disabled */

    if (!RunmodeIsUnittests() && !rs_ssh_hassh_is_enabled()) {

        if (!SigMatchSilentErrorEnabled(de_ctx, DETECT_AL_SSH_HASSH_SERVER)) {

            SCLogError("hassh support is not enabled");

        }

        return -2;

    }

    return 0;

}

static bool DetectSshHasshServerHashValidateCallback(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_ssh_hassh_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->flags & DETECT_CONTENT_NOCASE) {

                *sigerror = "ssh.hassh.server 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);

            }

            if (cd->content_len != 32) {

                *sigerror = "Invalid length of the specified ssh.hassh.server (should "

                            "be 32 characters long). This rule will therefore "

                            "never match.";

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

                return false;

            }

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

                if (!isxdigit(cd->content[i])) {

                    *sigerror = "Invalid ssh.hassh.server string (should be string of hexadecimal "

                                "characters)."

                                "This rule will therefore never match.";

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

                    return false;

                }

            }

        }

    }

    return true;

}

static void DetectSshHasshServerHashSetupCallback(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_ssh_hassh_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;

            uint32_t u;

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

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

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

                }

            }

            SpmDestroyCtx(cd->spm_ctx);

            cd->spm_ctx =

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

        }

    }

}

/**

 * \brief Registration function for hasshServer keyword.

 */

void DetectSshHasshServerRegister(void) 

{

    sigmatch_table[DETECT_AL_SSH_HASSH_SERVER].name = KEYWORD_NAME;

    sigmatch_table[DETECT_AL_SSH_HASSH_SERVER].alias = KEYWORD_ALIAS;

    sigmatch_table[DETECT_AL_SSH_HASSH_SERVER].desc = BUFFER_NAME " sticky buffer";

    sigmatch_table[DETECT_AL_SSH_HASSH_SERVER].url = "/rules/" KEYWORD_DOC;

    sigmatch_table[DETECT_AL_SSH_HASSH_SERVER].Setup = DetectSshHasshServerSetup;

    sigmatch_table[DETECT_AL_SSH_HASSH_SERVER].flags |= SIGMATCH_INFO_STICKY_BUFFER | SIGMATCH_NOOPT;

    DetectAppLayerMpmRegister2(BUFFER_NAME, SIG_FLAG_TOCLIENT, 2, 

            PrefilterGenericMpmRegister, GetSshData, 

            ALPROTO_SSH, SshStateBannerDone);

    DetectAppLayerInspectEngineRegister2(BUFFER_NAME, ALPROTO_SSH, 

            SIG_FLAG_TOCLIENT, SshStateBannerDone, 

            DetectEngineInspectBufferGeneric, GetSshData);

    DetectBufferTypeSetDescriptionByName(BUFFER_NAME, BUFFER_DESC);

    g_ssh_hassh_buffer_id = DetectBufferTypeGetByName(BUFFER_NAME);

    DetectBufferTypeRegisterSetupCallback(BUFFER_NAME, DetectSshHasshServerHashSetupCallback);

    DetectBufferTypeRegisterValidateCallback(BUFFER_NAME, DetectSshHasshServerHashValidateCallback);

}