java.lang.IllegalArgumentException: Not a directory

@红薯 你好，想跟你请教个问题：web项目本来部署在windows server上运行正常，采用的是oschina开源的代码，现在迁移到Ubuntu server14.04，项目部署在/var/lib/tomcat7/webapps/cmsis，当用户上传文件时出现如下错误：

java.lang.IllegalArgumentException: Not a directory: /var/lib/tomcat7/webapps/cmsis/WEB-INF/tmp/Ri4rDuQL3W
	at com.oreilly.servlet.MultipartRequest.<init>(MultipartRequest.java:214)
	at com.oreilly.servlet.MultipartRequest.<init>(MultipartRequest.java:173)
	at my.mvc.MultipartRequest.<init>(MultipartRequest.java:26)
	at my.mvc.RequestContext._AutoUploadRequest(RequestContext.java:204)
	at my.mvc.RequestContext.begin(RequestContext.java:119)
	at my.mvc.URLMappingFilter.doFilter(URLMappingFilter.java:103)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)

其中at my.mvc.RequestContext._AutoUploadRequest(RequestContext.java:204)

//上传的临时目录设置
upload_tmp_path = webroot + "WEB-INF" + File.separator + "tmp" + File.separator;

请问这是什么原因，是文件夹权限问题吗？一般tomcat在生成环境部署的时候，对于用户上传的文件夹应该怎么处理呢？谢谢！