https://bz.apache.org/bugzilla/show_bug.cgi?id=69821
Bug ID: 69821
Summary: `AbstractProcessor` risks `NullPointerException`
crashes due to race conditions with `volatile
socketWrapper`. Fix with final local references and
null checks.
Product: Tomcat 11
Version: 11.0.0
Hardware: PC
OS: Linux
Status: NEW
Severity: major
Priority: P2
Component: Connectors
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: -------
Created attachment 40103
--> https://bz.apache.org/bugzilla/attachment.cgi?id=40103&action=edit
a full report about bug
## **1. Null Pointer Exception Risks**
### **Location**:
Multiple methods throughout the `AbstractProcessor` class, including:
- `execute(Runnable runnable)`
- `processSocketEvent(SocketEvent event, boolean dispatch)`
- `executeDispatches()`
- `populateRequestAttributeRemoteHost()`
- `populateSslRequestAttributes()` (indirectly, via `sslSupport`)
### **Severity**:
**High** - This can lead to runtime crashes, service interruptions, and
unstable behavior in production environments.
---
## **Detailed Analysis**
### **Root Cause**:
The class maintains a `socketWrapper` field that is declared as `volatile`:
```java
protected volatile SocketWrapperBase<?> socketWrapper = null;
```
While this ensures visibility across threads, it does not guarantee atomicity
of compound operations. The field can be set to `null` at any time by another
thread, leading to race conditions between null checks and actual usage.
### **Problematic Code Examples**:
1. **In `execute()` method**:
```java
protected void execute(Runnable runnable) {
SocketWrapperBase<?> socketWrapper = this.socketWrapper; // Local copy
if (socketWrapper == null) {
throw new
RejectedExecutionException(sm.getString("abstractProcessor.noExecute"));
}
socketWrapper.execute(runnable); // socketWrapper could become null after
check
}
```
2. **In `processSocketEvent()` method**:
```java
protected void processSocketEvent(SocketEvent event, boolean dispatch) {
SocketWrapperBase<?> socketWrapper = this.getSocketWrapper(); // Returns
this.socketWrapper
if (socketWrapper != null) {
socketWrapper.processSocket(event, dispatch); // socketWrapper could
become null after check
}
// No handling for when socketWrapper is null
}
```
3. **In various population methods**:
```java
protected void populateRequestAttributeRemoteHost() {
if (this.getPopulateRequestAttributesFromSocket() && this.socketWrapper !=
null) {
this.request.remoteHost().setString(this.socketWrapper.getRemoteHost());
// socketWrapper could become null during method execution
}
}
```
### **Impact**:
- **NullPointerException**: This will crash the current request processing
thread.
- **Service Disruption**: If this happens frequently, it can degrade the
overall performance and availability of the web server.
- **Difficult Debugging**: Since the issue is timing-dependent, it may be hard
to reproduce and diagnose in production environments.
### **Concurrency Scenario**:
1. **Thread A** checks `socketWrapper != null` and passes the check.
2. **Thread B** sets `socketWrapper = null` (e.g., during recycling or
connection close).
3. **Thread A** proceeds to call a method on `socketWrapper`, causing a
`NullPointerException`.
---
## **Recommendations**
### **Immediate Fix**:
For all methods that use `socketWrapper`, implement a safe local reference
pattern:
```java
protected void execute(Runnable runnable) {
final SocketWrapperBase<?> socketWrapper = this.socketWrapper; // Final
local copy
if (socketWrapper == null) {
throw new
RejectedExecutionException(sm.getString("abstractProcessor.noExecute"));
}
socketWrapper.execute(runnable); // Safe usage of local reference
}
```
### **Additional Safeguards**:
1. **Add Null Checks in `getSocketWrapper()`**:
```java
protected final SocketWrapperBase<?> getSocketWrapper() {
SocketWrapperBase<?> wrapper = this.socketWrapper;
if (wrapper == null) {
throw new IllegalStateException("SocketWrapper is not available");
}
return wrapper;
}
```
2. **Implement Proper Error Handling**:
```java
protected void processSocketEvent(SocketEvent event, boolean dispatch) {
try {
final SocketWrapperBase<?> socketWrapper = this.socketWrapper;
if (socketWrapper != null) {
socketWrapper.processSocket(event, dispatch);
} else {
log.debug("SocketWrapper is null, ignoring event: " + event);
}
} catch (NullPointerException e) {
log.warn("Failed to process socket event due to null wrapper", e);
}
}
```
3. **Review Lifecycle Management**: Ensure that `socketWrapper` is never set to
`null` while there are pending operations. Consider using a `AtomicReference`
for more controlled access.
### **Testing Strategy**:
1. **Concurrency Tests**: Implement stress tests that simulate rapid connection
establishment and teardown.
2. **Null Injection**: Use mocking frameworks to intentionally set
`socketWrapper` to `null` during method execution.
3. **Static Analysis**: Use tools like SpotBugs or SonarQube to detect similar
patterns across the codebase.
---
## **Conclusion**
The null pointer exception risk in `AbstractProcessor` is a critical issue that
requires immediate attention. While the `volatile` keyword ensures visibility,
it does not prevent race conditions. The recommended solution is to use local
final references combined with additional null checks and proper error handling
to ensure graceful degradation instead of runtime exceptions.
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