detect-filemagic.c

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/* Copyright (C) 2007-2014 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 "threads.h"
#include "debug.h"
#include "decode.h"

#include "detect.h"
#include "detect-parse.h"

#include "detect-engine.h"
#include "detect-engine-mpm.h"
#include "detect-engine-state.h"

#include "flow.h"
#include "flow-var.h"
#include "flow-util.h"

#include "util-debug.h"
#include "util-spm-bm.h"
#include "util-magic.h"
#include "util-print.h"

#include "util-unittest.h"
#include "util-unittest-helper.h"

#include "app-layer.h"

#include "stream-tcp.h"

#include "detect-filemagic.h"

#include "conf.h"

#ifndef HAVE_MAGIC

static int DetectFilemagicSetupNoSupport (DetectEngineCtx *de_ctx, Signature *s, const char *str)
{
    SCLogError(SC_ERR_NO_MAGIC_SUPPORT, "no libmagic support built in, needed for filemagic keyword");
    return -1;
}

/**
 * \brief Registration function for keyword: filemagic
 */
void DetectFilemagicRegister(void)
{
    sigmatch_table[DETECT_FILEMAGIC].name = "filemagic";
    sigmatch_table[DETECT_FILEMAGIC].desc = "match on the information libmagic returns about a file";
    sigmatch_table[DETECT_FILEMAGIC].url = "https://suricata.readthedocs.io/en/latest/rules/file-keywords.html#filemagic";
    sigmatch_table[DETECT_FILEMAGIC].Setup = DetectFilemagicSetupNoSupport;
    sigmatch_table[DETECT_FILEMAGIC].flags = SIGMATCH_QUOTES_MANDATORY|SIGMATCH_HANDLE_NEGATION;
}

#else /* HAVE_MAGIC */

static int DetectFilemagicMatch (ThreadVars *, DetectEngineThreadCtx *, Flow *,
        uint8_t, File *, const Signature *, const SigMatchCtx *);
static int DetectFilemagicSetup (DetectEngineCtx *, Signature *, const char *);
static void DetectFilemagicRegisterTests(void);
static void DetectFilemagicFree(void *);
static int g_file_match_list_id = 0;

/**
 * \brief Registration function for keyword: filemagic
 */
void DetectFilemagicRegister(void)
{
    sigmatch_table[DETECT_FILEMAGIC].name = "filemagic";
    sigmatch_table[DETECT_FILEMAGIC].desc = "match on the information libmagic returns about a file";
    sigmatch_table[DETECT_FILEMAGIC].url = DOC_URL DOC_VERSION "/rules/file-keywords.html#filemagic";
    sigmatch_table[DETECT_FILEMAGIC].FileMatch = DetectFilemagicMatch;
    sigmatch_table[DETECT_FILEMAGIC].Setup = DetectFilemagicSetup;
    sigmatch_table[DETECT_FILEMAGIC].Free  = DetectFilemagicFree;
    sigmatch_table[DETECT_FILEMAGIC].RegisterTests = DetectFilemagicRegisterTests;
    sigmatch_table[DETECT_FILEMAGIC].flags = SIGMATCH_QUOTES_MANDATORY|SIGMATCH_HANDLE_NEGATION;

    g_file_match_list_id = DetectBufferTypeRegister("files");

    SCLogDebug("registering filemagic rule option");
    return;
}

#define FILEMAGIC_MIN_SIZE  512

/**
 *  \brief run the magic check
 *
 *  \param file the file
 *
 *  \retval -1 error
 *  \retval 0 ok
 */
int FilemagicGlobalLookup(File *file)
{
    if (file == NULL || FileDataSize(file) == 0) {
        SCReturnInt(-1);
    }

    const uint8_t *data = NULL;
    uint32_t data_len = 0;
    uint64_t offset = 0;

    StreamingBufferGetData(file->sb,
                           &data, &data_len, &offset);
    if (offset == 0) {
        if (FileDataSize(file) >= FILEMAGIC_MIN_SIZE) {
            file->magic = MagicGlobalLookup(data, data_len);
        } else if (file->state >= FILE_STATE_CLOSED) {
            file->magic = MagicGlobalLookup(data, data_len);
        }
    }

    SCReturnInt(0);
}

/**
 *  \brief run the magic check
 *
 *  \param file the file
 *
 *  \retval -1 error
 *  \retval 0 ok
 */
static int FilemagicThreadLookup(magic_t *ctx, File *file)
{
    if (ctx == NULL || file == NULL || FileDataSize(file) == 0) {
        SCReturnInt(-1);
    }

    const uint8_t *data = NULL;
    uint32_t data_len = 0;
    uint64_t offset = 0;

    StreamingBufferGetData(file->sb,
                           &data, &data_len, &offset);
    if (offset == 0) {
        if (FileDataSize(file) >= FILEMAGIC_MIN_SIZE) {
            file->magic = MagicThreadLookup(ctx, data, data_len);
        } else if (file->state >= FILE_STATE_CLOSED) {
            file->magic = MagicThreadLookup(ctx, data, data_len);
        }
    }
    SCReturnInt(0);
}

/**
 * \brief match the specified filemagic
 *
 * \param t thread local vars
 * \param det_ctx pattern matcher thread local data
 * \param f *LOCKED* flow
 * \param flags direction flags
 * \param file file being inspected
 * \param s signature being inspected
 * \param m sigmatch that we will cast into DetectFilemagicData
 *
 * \retval 0 no match
 * \retval 1 match
 */
static int DetectFilemagicMatch (ThreadVars *t, DetectEngineThreadCtx *det_ctx,
        Flow *f, uint8_t flags, File *file, const Signature *s, const SigMatchCtx *m)
{
    SCEnter();
    int ret = 0;
    DetectFilemagicData *filemagic = (DetectFilemagicData *)m;

    DetectFilemagicThreadData *tfilemagic = (DetectFilemagicThreadData *)DetectThreadCtxGetKeywordThreadCtx(det_ctx, filemagic->thread_ctx_id);
    if (tfilemagic == NULL) {
        SCReturnInt(0);
    }

    if (file->magic == NULL) {
        FilemagicThreadLookup(&tfilemagic->ctx, file);
    }

    if (file->magic != NULL) {
        SCLogDebug("magic %s", file->magic);

        /* we include the \0 in the inspection, so patterns can match on the
         * end of the string. */
        if (BoyerMooreNocase(filemagic->name, filemagic->len, (uint8_t *)file->magic,
                    strlen(file->magic) + 1, filemagic->bm_ctx) != NULL)
        {
#ifdef DEBUG
            if (SCLogDebugEnabled()) {
                char *name = SCMalloc(filemagic->len + 1);
                if (name != NULL) {
                    memcpy(name, filemagic->name, filemagic->len);
                    name[filemagic->len] = '\0';
                    SCLogDebug("will look for filemagic %s", name);
                    SCFree(name);
                }
            }
#endif

            if (!(filemagic->flags & DETECT_CONTENT_NEGATED)) {
                ret = 1;
            }
        } else if (filemagic->flags & DETECT_CONTENT_NEGATED) {
            SCLogDebug("negated match");
            ret = 1;
        }
    }

    SCReturnInt(ret);
}

/**
 * \brief Parse the filemagic keyword
 *
 * \param idstr Pointer to the user provided option
 *
 * \retval filemagic pointer to DetectFilemagicData on success
 * \retval NULL on failure
 */
static DetectFilemagicData *DetectFilemagicParse (const char *str, bool negate)
{
    DetectFilemagicData *filemagic = NULL;

    /* We have a correct filemagic option */
    filemagic = SCMalloc(sizeof(DetectFilemagicData));
    if (unlikely(filemagic == NULL))
        goto error;

    memset(filemagic, 0x00, sizeof(DetectFilemagicData));

    if (DetectContentDataParse ("filemagic", str, &filemagic->name, &filemagic->len) == -1) {
        goto error;
    }

    filemagic->bm_ctx = BoyerMooreNocaseCtxInit(filemagic->name, filemagic->len);
    if (filemagic->bm_ctx == NULL) {
        goto error;
    }

    if (negate) {
        filemagic->flags |= DETECT_CONTENT_NEGATED;
    }

    SCLogDebug("flags %02X", filemagic->flags);
    if (filemagic->flags & DETECT_CONTENT_NEGATED) {
        SCLogDebug("negated filemagic");
    }

#ifdef DEBUG
    if (SCLogDebugEnabled()) {
        char *name = SCMalloc(filemagic->len + 1);
        if (name != NULL) {
            memcpy(name, filemagic->name, filemagic->len);
            name[filemagic->len] = '\0';
            SCLogDebug("will look for filemagic %s", name);
            SCFree(name);
        }
    }
#endif

    return filemagic;

error:
    if (filemagic != NULL)
        DetectFilemagicFree(filemagic);
    return NULL;
}

static void *DetectFilemagicThreadInit(void *data)
{
    const char *filename = NULL;
    FILE *fd = NULL;
    DetectFilemagicData *filemagic = (DetectFilemagicData *)data;
    BUG_ON(filemagic == NULL);

    DetectFilemagicThreadData *t = SCMalloc(sizeof(DetectFilemagicThreadData));
    if (unlikely(t == NULL)) {
        SCLogError(SC_ERR_MEM_ALLOC, "couldn't alloc ctx memory");
        return NULL;
    }
    memset(t, 0x00, sizeof(DetectFilemagicThreadData));

    t->ctx = magic_open(0);
    if (t->ctx == NULL) {
        SCLogError(SC_ERR_MAGIC_OPEN, "magic_open failed: %s", magic_error(t->ctx));
        goto error;
    }

    (void)ConfGet("magic-file", &filename);
    if (filename != NULL) {
        if (strlen(filename) == 0) {
            /* set filename to NULL on *nix systems so magic_load uses system default path (see man libmagic) */
            SCLogInfo("using system default magic-file");
            filename = NULL;
        }
        else {
            SCLogInfo("using magic-file %s", filename);

            if ( (fd = fopen(filename, "r")) == NULL) {
                SCLogWarning(SC_ERR_FOPEN, "Error opening file: \"%s\": %s", filename, strerror(errno));
                goto error;
            }
            fclose(fd);
        }
    }

    if (magic_load(t->ctx, filename) != 0) {
        SCLogError(SC_ERR_MAGIC_LOAD, "magic_load failed: %s", magic_error(t->ctx));
        goto error;
    }

    return (void *)t;

error:
    if (t->ctx)
        magic_close(t->ctx);
    SCFree(t);
    return NULL;
}

static void DetectFilemagicThreadFree(void *ctx)
{
    if (ctx != NULL) {
        DetectFilemagicThreadData *t = (DetectFilemagicThreadData *)ctx;
        if (t->ctx)
            magic_close(t->ctx);
        SCFree(t);
    }
}

/**
 * \brief this function is used to parse filemagic options
 * \brief into the current signature
 *
 * \param de_ctx pointer to the Detection Engine Context
 * \param s pointer to the Current Signature
 * \param str pointer to the user provided "filemagic" option
 *
 * \retval 0 on Success
 * \retval -1 on Failure
 */
static int DetectFilemagicSetup (DetectEngineCtx *de_ctx, Signature *s, const char *str)
{
    DetectFilemagicData *filemagic = NULL;
    SigMatch *sm = NULL;

    filemagic = DetectFilemagicParse(str, s->init_data->negated);
    if (filemagic == NULL)
        goto error;

    filemagic->thread_ctx_id = DetectRegisterThreadCtxFuncs(de_ctx, "filemagic",
            DetectFilemagicThreadInit, (void *)filemagic,
            DetectFilemagicThreadFree, 1);
    if (filemagic->thread_ctx_id == -1)
        goto error;

    /* Okay so far so good, lets get this into a SigMatch
     * and put it in the Signature. */
    sm = SigMatchAlloc();
    if (sm == NULL)
        goto error;

    sm->type = DETECT_FILEMAGIC;
    sm->ctx = (void *)filemagic;

    SigMatchAppendSMToList(s, sm, g_file_match_list_id);

    s->file_flags |= (FILE_SIG_NEED_FILE|FILE_SIG_NEED_MAGIC);
    return 0;

error:
    if (filemagic != NULL)
        DetectFilemagicFree(filemagic);
    if (sm != NULL)
        SCFree(sm);
    return -1;
}

/**
 * \brief this function will free memory associated with DetectFilemagicData
 *
 * \param filemagic pointer to DetectFilemagicData
 */
static void DetectFilemagicFree(void *ptr)
{
    if (ptr != NULL) {
        DetectFilemagicData *filemagic = (DetectFilemagicData *)ptr;
        if (filemagic->bm_ctx != NULL) {
            BoyerMooreCtxDeInit(filemagic->bm_ctx);
        }
        if (filemagic->name != NULL)
            SCFree(filemagic->name);
        SCFree(filemagic);
    }
}

#ifdef UNITTESTS /* UNITTESTS */

/**
 * \test DetectFilemagicTestParse01
 */
static int DetectFilemagicTestParse01 (void)
{
    DetectFilemagicData *dnd = DetectFilemagicParse("secret.pdf", false);
    if (dnd != NULL) {
        DetectFilemagicFree(dnd);
        return 1;
    }
    return 0;
}

/**
 * \test DetectFilemagicTestParse02
 */
static int DetectFilemagicTestParse02 (void)
{
    int result = 0;

    DetectFilemagicData *dnd = DetectFilemagicParse("backup.tar.gz", false);
    if (dnd != NULL) {
        if (dnd->len == 13 && memcmp(dnd->name, "backup.tar.gz", 13) == 0) {
            result = 1;
        }

        DetectFilemagicFree(dnd);
        return result;
    }
    return 0;
}

/**
 * \test DetectFilemagicTestParse03
 */
static int DetectFilemagicTestParse03 (void)
{
    int result = 0;

    DetectFilemagicData *dnd = DetectFilemagicParse("cmd.exe", false);
    if (dnd != NULL) {
        if (dnd->len == 7 && memcmp(dnd->name, "cmd.exe", 7) == 0) {
            result = 1;
        }

        DetectFilemagicFree(dnd);
        return result;
    }
    return 0;
}

#endif /* UNITTESTS */

/**
 * \brief this function registers unit tests for DetectFilemagic
 */
void DetectFilemagicRegisterTests(void)
{
#ifdef UNITTESTS /* UNITTESTS */
    UtRegisterTest("DetectFilemagicTestParse01", DetectFilemagicTestParse01);
    UtRegisterTest("DetectFilemagicTestParse02", DetectFilemagicTestParse02);
    UtRegisterTest("DetectFilemagicTestParse03", DetectFilemagicTestParse03);
#endif /* UNITTESTS */
}

#endif /* HAVE_MAGIC */