ClamAV学习【4】——cli_magic_scandesc函数浏览

今晚继续浏览ClamAV代码，挖掘到了cli_magic_scandesc函数，发现前面包装了很多次扫描函数，这里就是最后一层的感觉。一些扫描限制判断加上文件类型判断，采用不同扫描函数处理。

（PS:发现这些函数个头都很大，虽然按着功能分段好理解，但是书本不是说一个函数一个功能模块么？难道是不实际，还是理解错误？）

代码分析如下：

//magic，说明这很神奇
int cli_magic_scandesc(int desc, cli_ctx *ctx)
{
	int ret = CL_CLEAN;
	cli_file_t type, dettype = 0;
	struct stat sb;
	uint8_t typercg = 1;

	//获取文件属性stat结构
    if(fstat(desc, &sb) == -1) {
	cli_errmsg("magic_scandesc: Can't fstat descriptor %d
", desc);
	return CL_EIO;
    }

	//文件太小无需扫描
    if(sb.st_size <= 5) {
	cli_dbgmsg("Small data (%u bytes)
", (unsigned int) sb.st_size);
	return CL_CLEAN;
    }

	//引擎已经构建
    if(!ctx->engine) {
	cli_errmsg("CRITICAL: engine == NULL
");
	return CL_EMALFDB;
    }

	//默认模式扫描
    if(!ctx->options) { /* raw mode (stdin, etc.) */
	cli_dbgmsg("Raw mode: No support for special files
");
	if((ret = cli_scandesc(desc, ctx, 0, 0, NULL, AC_SCAN_VIR)) == CL_VIRUS)
	    cli_dbgmsg("%s found in descriptor %d
", *ctx->virname, desc);
	return ret;
    }

	//是否超过设置的扫描限制
    if(cli_updatelimits(ctx, sb.st_size)!=CL_CLEAN)
        return CL_CLEAN;

	//邮件或者压缩文件扫描
    if((SCAN_MAIL || SCAN_ARCHIVE) && ctx->limits && ctx->limits->maxreclevel && ctx->recursion > ctx->limits->maxreclevel) {
        cli_dbgmsg("Archive recursion limit exceeded (level = %u).
", ctx->recursion);
	return CL_CLEAN;
    }

	//定位文件，找到文件类型
    lseek(desc, 0, SEEK_SET);
    type = cli_filetype2(desc, ctx->engine);
    if(type == CL_TYPE_ERROR) {
	cli_dbgmsg("cli_magic_scandesc: cli_filetype2 returned CL_TYPE_ERROR
");
	return CL_EIO;
    }
    lseek(desc, 0, SEEK_SET);

	//非忽略类型还有个什么。需要研究
    if(type != CL_TYPE_IGNORED && ctx->engine->sdb) {
	if((ret = cli_scanraw(desc, ctx, type, 0, &dettype)) == CL_VIRUS)
	    return CL_VIRUS;
	lseek(desc, 0, SEEK_SET);
    }

    ctx->recursion++;

	//根据不同的类型，让文件见鬼去吧
    switch(type) {
	case CL_TYPE_IGNORED:
	    break;

	case CL_TYPE_RAR:
#ifdef ENABLE_UNRAR
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_RAR))
		ret = cli_scanrar(desc, ctx, 0, NULL);
#else
	    cli_warnmsg("RAR code not compiled-in
");
#endif
	    break;

	case CL_TYPE_ZIP:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_ZIP))
		ret = cli_unzip(desc, ctx);
	    break;

	case CL_TYPE_GZ:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_GZ))
		ret = cli_scangzip(desc, ctx);
	    break;

	case CL_TYPE_BZ:
#ifdef HAVE_BZLIB_H
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_BZ))
		ret = cli_scanbzip(desc, ctx);
#endif
	    break;
	case CL_TYPE_ARJ:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_ARJ))
		ret = cli_scanarj(desc, ctx, 0, NULL);
	    break;

        case CL_TYPE_NULSFT:
	  if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_NSIS))
		ret = cli_scannulsft(desc, ctx, 0);
	    break;

        case CL_TYPE_AUTOIT:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_AUTOIT))
		ret = cli_scanautoit(desc, ctx, 23);
	    break;

	case CL_TYPE_MSSZDD:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_SZDD))
		ret = cli_scanszdd(desc, ctx);
	    break;

	case CL_TYPE_MSCAB:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_CAB))
		ret = cli_scanmscab(desc, ctx, 0);
	    break;

	case CL_TYPE_HTML:
	    if(SCAN_HTML && (DCONF_DOC & DOC_CONF_HTML))
		ret = cli_scanhtml(desc, ctx);
	    break;

	case CL_TYPE_HTML_UTF16:
	    if(SCAN_HTML && (DCONF_DOC & DOC_CONF_HTML))
		ret = cli_scanhtml_utf16(desc, ctx);
	    break;

	case CL_TYPE_SCRIPT:
	    if((DCONF_DOC & DOC_CONF_SCRIPT) && dettype != CL_TYPE_HTML)
	        ret = cli_scanscript(desc, ctx);
	    break;

	case CL_TYPE_RTF:
	    if(SCAN_ARCHIVE && (DCONF_DOC & DOC_CONF_RTF))
		ret = cli_scanrtf(desc, ctx);
	    break;

	case CL_TYPE_MAIL:
	    if(SCAN_MAIL && (DCONF_MAIL & MAIL_CONF_MBOX))
		ret = cli_scanmail(desc, ctx);
	    break;

	case CL_TYPE_TNEF:
	    if(SCAN_MAIL && (DCONF_MAIL & MAIL_CONF_TNEF))
		ret = cli_scantnef(desc, ctx);
	    break;

	case CL_TYPE_UUENCODED:
	    if(DCONF_OTHER & OTHER_CONF_UUENC)
		ret = cli_scanuuencoded(desc, ctx);
	    break;

	case CL_TYPE_MSCHM:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_CHM))
		ret = cli_scanmschm(desc, ctx);
	    break;

	case CL_TYPE_MSOLE2:
	    if(SCAN_OLE2 && (DCONF_ARCH & ARCH_CONF_OLE2))
		ret = cli_scanole2(desc, ctx);
	    break;

	case CL_TYPE_POSIX_TAR:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_TAR))
		ret = cli_scantar(desc, ctx, 1);
	    break;

	case CL_TYPE_OLD_TAR:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_TAR))
		ret = cli_scantar(desc, ctx, 0);
	    break;

	case CL_TYPE_BINHEX:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_BINHEX))
		ret = cli_scanbinhex(desc, ctx);
	    break;

	case CL_TYPE_SCRENC:
	    if(DCONF_OTHER & OTHER_CONF_SCRENC)
		ret = cli_scanscrenc(desc, ctx);
	    break;

	case CL_TYPE_RIFF:
	    if(SCAN_ALGO && (DCONF_OTHER & OTHER_CONF_RIFF))
		ret = cli_scanriff(desc, ctx->virname);
	    break;

	case CL_TYPE_GRAPHICS:
	    if(SCAN_ALGO && (DCONF_OTHER & OTHER_CONF_JPEG))
		ret = cli_scanjpeg(desc, ctx->virname);
	    break;

        case CL_TYPE_PDF: /* FIXMELIMITS: pdf should be an archive! */
	    if(SCAN_PDF && (DCONF_DOC & DOC_CONF_PDF))
		ret = cli_scanpdf(desc, ctx, 0);
	    break;

	case CL_TYPE_CRYPTFF:
	    if(DCONF_OTHER & OTHER_CONF_CRYPTFF)
		ret = cli_scancryptff(desc, ctx);
	    break;

	case CL_TYPE_ELF:
	    if(SCAN_ELF && ctx->dconf->elf)
		ret = cli_scanelf(desc, ctx);
	    break;

	case CL_TYPE_SIS:
	    if(SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_SIS))
		ret = cli_scansis(desc, ctx);
	    break;

	case CL_TYPE_BINARY_DATA:
	    ret = cli_check_mydoom_log(desc, ctx->virname);
	    break;

	default:
	    break;
    }

    ctx->recursion--;

	//没有检查植入性pe文件
    if(type == CL_TYPE_ZIP && SCAN_ARCHIVE && (DCONF_ARCH & ARCH_CONF_ZIP)) {
	if(sb.st_size > 1048576) {
	    cli_dbgmsg("cli_magic_scandesc: Not checking for embedded PEs (zip file > 1 MB)
");
	    typercg = 0;
	}
    }

    /* CL_TYPE_HTML: raw HTML files are not scanned, unless safety measure activated via DCONF */
    if(type != CL_TYPE_IGNORED && (type != CL_TYPE_HTML || !(DCONF_DOC & DOC_CONF_HTML_SKIPRAW)) && ret != CL_VIRUS && !ctx->engine->sdb) {
	if(cli_scanraw(desc, ctx, type, typercg, &dettype) == CL_VIRUS)
	    return CL_VIRUS;
    }

    ctx->recursion++;
    lseek(desc, 0, SEEK_SET);
    switch(type) {
	case CL_TYPE_TEXT_ASCII:
	    if((DCONF_DOC & DOC_CONF_SCRIPT) && dettype != CL_TYPE_HTML)
	        ret = cli_scanscript(desc, ctx);
	    break;
	/* Due to performance reasons all executables were first scanned
	 * in raw mode. Now we will try to unpack them
	 */
	case CL_TYPE_MSEXE:
	    if(SCAN_PE && ctx->dconf->pe)
		ret = cli_scanpe(desc, ctx);
	    break;

	default:
	    break;
    }
    ctx->recursion--;

    switch(ret) {
	case CL_EFORMAT:
	case CL_EMAXREC:
	case CL_EMAXSIZE:
	case CL_EMAXFILES:
	    cli_dbgmsg("Descriptor[%d]: %s
", desc, cl_strerror(ret));
	    return CL_CLEAN;
	default:
	    return ret;
    }
}

原文：http://blog.csdn.net/betabin/article/details/7424762