skywalking修复log4j漏洞

漏洞产生的原因，在于 Log4j2 允许 JNDI 任意连接服务器，在 org.apache.logging.log4j.core.lookup.JndiLookup#lookup 中，代码如下：

@Override
public String lookup(final LogEvent event, final String key) {
    if (key == null) {
        return null;
    }
    final String jndiName = convertJndiName(key);
    try (final JndiManager jndiManager = JndiManager.getDefaultManager()) {
        return Objects.toString(jndiManager.lookup(jndiName), null);
    } catch (final NamingException e) {
        LOGGER.warn(LOOKUP, "Error looking up JNDI resource [{}].", jndiName, e);
        return null;
    }
}

该代码只有在 log.info("{}", "${jndi:xxxx/xx}")时会触发。

还有就是${java:vm}会输出虚拟机信息。

具体原因是因为org.apache.logging.log4j.core.lookup.JavaLookup#lookup，会输出一些系统相关信息。

前面简单了解了字节码增强技术，这里可以想到如果执行到了lookup方法的时候就直接返回不行了么。我们来看下实战。

创建JndiLookupActivation

package org.apache.skywalking.apm.plugin.custom;

import net.bytebuddy.description.method.MethodDescription;
import net.bytebuddy.matcher.ElementMatcher;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.ConstructorInterceptPoint;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.InstanceMethodsInterceptPoint;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.ClassInstanceMethodsEnhancePluginDefine;
import org.apache.skywalking.apm.agent.core.plugin.match.ClassMatch;
import org.apache.skywalking.apm.agent.core.plugin.match.MultiClassNameMatch;

import static net.bytebuddy.matcher.ElementMatchers.named;

public class JndiLookupActivation extends ClassInstanceMethodsEnhancePluginDefine {

    private static final String INTERCEPT_CLASS = "org.apache.skywalking.apm.plugin.custom.JndiLookupMethodInterceptor";
    private static final String ENHANCE_CLASS = "org.apache.logging.log4j.core.lookup.JndiLookup";
    private static final String ENHANCE_CLASS_2 = "org.apache.logging.log4j.core.lookup.JavaLookup";
    private static final String ENHANCE_METHOD = "lookup";

    @Override
    public ConstructorInterceptPoint[] getConstructorsInterceptPoints() {
        return new ConstructorInterceptPoint[0];
    }

    @Override
    public InstanceMethodsInterceptPoint[] getInstanceMethodsInterceptPoints() {
        return new InstanceMethodsInterceptPoint[]{
                new InstanceMethodsInterceptPoint() {
                    @Override
                    public ElementMatcher getMethodsMatcher() {
                        return named(ENHANCE_METHOD);
                    }

                    @Override
                    public String getMethodsInterceptor() {
                        return INTERCEPT_CLASS;
                    }

                    @Override
                    public boolean isOverrideArgs() {
                        return true;
                    }
                }
        };
    }

    @Override
    protected ClassMatch enhanceClass() {
        return MultiClassNameMatch.byMultiClassMatch(ENHANCE_CLASS_2, ENHANCE_CLASS);
    }
}

创建JndiLookupMethodInterceptor

package org.apache.skywalking.apm.plugin.custom;

import org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.EnhancedInstance;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstanceMethodsAroundInterceptor;
import org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.MethodInterceptResult;

import java.lang.reflect.Method;

public class JndiLookupMethodInterceptor implements InstanceMethodsAroundInterceptor {

    @Override
    public void beforeMethod(EnhancedInstance objInst, Method method, Object[] allArguments, Class[] argumentsTypes,
                             MethodInterceptResult result) throws Throwable {
        result.defineReturnValue(null);
    }

    @Override
    public Object afterMethod(EnhancedInstance objInst, Method method, Object[] allArguments, Class[] argumentsTypes,
                              Object ret) throws Throwable {
        return ret;
    }

    @Override
    public void handleMethodException(EnhancedInstance objInst, Method method, Object[] allArguments,
                                      Class[] argumentsTypes, Throwable t) {
    }

}

在skywalking-plugin.def配置

jndi-look-up-1.0.x=org.apache.skywalking.apm.plugin.custom.JndiLookupActivation

给代码配上agent

-javaagent:/Users/qinfuxiang/IdeaProjects/skywalking-java/skywalking-agent/skywalking-agent.jar
-Dskywalking.agent.service_name=demo
-Dskywalking.collector.backend_service=127.0.0.1:11800

启动在重新试下