Merge "Resolved UAF issue in RefBase fuzzer"

libutils/RefBase_fuzz.cpp

@@ -14,66 +14,156 @@
  * limitations under the License.
  */
 
-#include <atomic>
+#define LOG_TAG "RefBaseFuzz"
+
 #include <thread>
 
 #include "fuzzer/FuzzedDataProvider.h"
+#include "utils/Log.h"
+#include "utils/RWLock.h"
 #include "utils/RefBase.h"
 #include "utils/StrongPointer.h"
+
 using android::RefBase;
+using android::RWLock;
 using android::sp;
 using android::wp;
 
-static constexpr int REFBASE_INITIAL_STRONG_VALUE = (1 << 28);
-static constexpr int REFBASE_MAX_COUNT = 0xfffff;
-
-static constexpr int MAX_OPERATIONS = 100;
-static constexpr int MAX_THREADS = 10;
-
-bool canDecrementStrong(RefBase* ref) {
-    // There's an assert around decrementing the strong count too much that causes an artificial
-    // crash This is just running BAD_STRONG from RefBase
-    const int32_t count = ref->getStrongCount() - 1;
-    return !(count == 0 || ((count) & (~(REFBASE_MAX_COUNT | REFBASE_INITIAL_STRONG_VALUE))) != 0);
-}
-bool canDecrementWeak(RefBase* ref) {
-    const int32_t count = ref->getWeakRefs()->getWeakCount() - 1;
-    return !((count) == 0 || ((count) & (~REFBASE_MAX_COUNT)) != 0);
-}
-
+static constexpr int kMaxOperations = 100;
+static constexpr int kMaxThreads = 10;
 struct RefBaseSubclass : public RefBase {
-    RefBaseSubclass() {}
-    virtual ~RefBaseSubclass() {}
+  public:
+    RefBaseSubclass(bool* deletedCheck, RWLock& deletedMtx)
+        : mDeleted(deletedCheck), mRwLock(deletedMtx) {
+        RWLock::AutoWLock lock(mRwLock);
+        *mDeleted = false;
+        extendObjectLifetime(OBJECT_LIFETIME_WEAK);
+    }
+
+    virtual ~RefBaseSubclass() {
+        RWLock::AutoWLock lock(mRwLock);
+        *mDeleted = true;
+    }
+
+  private:
+    bool* mDeleted;
+    android::RWLock& mRwLock;
 };
 
-std::vector<std::function<void(RefBaseSubclass*)>> operations = {
-        [](RefBaseSubclass* ref) -> void { ref->getStrongCount(); },
-        [](RefBaseSubclass* ref) -> void { ref->printRefs(); },
-        [](RefBaseSubclass* ref) -> void { ref->getWeakRefs()->printRefs(); },
-        [](RefBaseSubclass* ref) -> void { ref->getWeakRefs()->getWeakCount(); },
-        [](RefBaseSubclass* ref) -> void { ref->getWeakRefs()->refBase(); },
-        [](RefBaseSubclass* ref) -> void { ref->incStrong(nullptr); },
-        [](RefBaseSubclass* ref) -> void {
-            if (canDecrementStrong(ref)) {
+// A thread-specific state object for ref
+struct RefThreadState {
+    size_t strongCount = 0;
+    size_t weakCount = 0;
+};
+
+RWLock gRefDeletedLock;
+bool gRefDeleted = false;
+bool gHasModifiedRefs = false;
+RefBaseSubclass* ref;
+RefBase::weakref_type* weakRefs;
+
+// These operations don't need locks as they explicitly check per-thread counts before running
+// they also have the potential to write to gRefDeleted, so must not be locked.
+const std::vector<std::function<void(RefThreadState*)>> kUnlockedOperations = {
+        [](RefThreadState* refState) -> void {
+            if (refState->strongCount > 0) {
                 ref->decStrong(nullptr);
+                gHasModifiedRefs = true;
+                refState->strongCount--;
             }
         },
-        [](RefBaseSubclass* ref) -> void { ref->forceIncStrong(nullptr); },
-        [](RefBaseSubclass* ref) -> void { ref->createWeak(nullptr); },
-        [](RefBaseSubclass* ref) -> void { ref->getWeakRefs()->attemptIncStrong(nullptr); },
-        [](RefBaseSubclass* ref) -> void { ref->getWeakRefs()->attemptIncWeak(nullptr); },
-        [](RefBaseSubclass* ref) -> void {
-            if (canDecrementWeak(ref)) {
-                ref->getWeakRefs()->decWeak(nullptr);
+        [](RefThreadState* refState) -> void {
+            if (refState->weakCount > 0) {
+                weakRefs->decWeak(nullptr);
+                gHasModifiedRefs = true;
+                refState->weakCount--;
             }
         },
-        [](RefBaseSubclass* ref) -> void { ref->getWeakRefs()->incWeak(nullptr); },
-        [](RefBaseSubclass* ref) -> void { ref->getWeakRefs()->printRefs(); },
 };
 
-void loop(RefBaseSubclass* loopRef, const std::vector<uint8_t>& fuzzOps) {
+const std::vector<std::function<void(RefThreadState*)>> kMaybeLockedOperations = {
+        // Read-only operations
+        [](RefThreadState*) -> void { ref->getStrongCount(); },
+        [](RefThreadState*) -> void { weakRefs->getWeakCount(); },
+        [](RefThreadState*) -> void { ref->printRefs(); },
+
+        // Read/write operations
+        [](RefThreadState* refState) -> void {
+            ref->incStrong(nullptr);
+            gHasModifiedRefs = true;
+            refState->strongCount++;
+        },
+        [](RefThreadState* refState) -> void {
+            ref->forceIncStrong(nullptr);
+            gHasModifiedRefs = true;
+            refState->strongCount++;
+        },
+        [](RefThreadState* refState) -> void {
+            ref->createWeak(nullptr);
+            gHasModifiedRefs = true;
+            refState->weakCount++;
+        },
+        [](RefThreadState* refState) -> void {
+            // This will increment weak internally, then attempt to
+            // promote it to strong. If it fails, it decrements weak.
+            // If it succeeds, the weak is converted to strong.
+            // Both cases net no weak reference change.
+            if (weakRefs->attemptIncStrong(nullptr)) {
+                refState->strongCount++;
+                gHasModifiedRefs = true;
+            }
+        },
+        [](RefThreadState* refState) -> void {
+            if (weakRefs->attemptIncWeak(nullptr)) {
+                refState->weakCount++;
+                gHasModifiedRefs = true;
+            }
+        },
+        [](RefThreadState* refState) -> void {
+            weakRefs->incWeak(nullptr);
+            gHasModifiedRefs = true;
+            refState->weakCount++;
+        },
+};
+
+void loop(const std::vector<uint8_t>& fuzzOps) {
+    RefThreadState state;
+    uint8_t lockedOpSize = kMaybeLockedOperations.size();
+    uint8_t totalOperationTypes = lockedOpSize + kUnlockedOperations.size();
     for (auto op : fuzzOps) {
-        operations[op % operations.size()](loopRef);
+        auto opVal = op % totalOperationTypes;
+        if (opVal >= lockedOpSize) {
+            kUnlockedOperations[opVal % lockedOpSize](&state);
+        } else {
+            // We only need to lock if we have no strong or weak count
+            bool shouldLock = state.strongCount == 0 && state.weakCount == 0;
+            if (shouldLock) {
+                gRefDeletedLock.readLock();
+                // If ref has deleted itself, we can no longer fuzz on this thread.
+                if (gRefDeleted) {
+                    // Unlock since we're exiting the loop here.
+                    gRefDeletedLock.unlock();
+                    return;
+                }
+            }
+            // Execute the locked operation
+            kMaybeLockedOperations[opVal](&state);
+            // Unlock if we locked.
+            if (shouldLock) {
+                gRefDeletedLock.unlock();
+            }
+        }
+    }
+
+    // Instead of explicitly freeing this, we're going to remove our weak and
+    // strong references.
+    for (; state.weakCount > 0; state.weakCount--) {
+        weakRefs->decWeak(nullptr);
+    }
+
+    // Clean up any strong references
+    for (; state.strongCount > 0; state.strongCount--) {
+        ref->decStrong(nullptr);
     }
 }
 
@@ -81,23 +171,35 @@ void spawnThreads(FuzzedDataProvider* dataProvider) {
     std::vector<std::thread> threads = std::vector<std::thread>();
 
     // Get the number of threads to generate
-    uint8_t count = dataProvider->ConsumeIntegralInRange<uint8_t>(1, MAX_THREADS);
-
+    uint8_t count = dataProvider->ConsumeIntegralInRange<uint8_t>(1, kMaxThreads);
     // Generate threads
     for (uint8_t i = 0; i < count; i++) {
-        RefBaseSubclass* threadRef = new RefBaseSubclass();
-        uint8_t opCount = dataProvider->ConsumeIntegralInRange<uint8_t>(1, MAX_OPERATIONS);
+        uint8_t opCount = dataProvider->ConsumeIntegralInRange<uint8_t>(1, kMaxOperations);
         std::vector<uint8_t> threadOperations = dataProvider->ConsumeBytes<uint8_t>(opCount);
-        std::thread tmp = std::thread(loop, threadRef, threadOperations);
-        threads.push_back(move(tmp));
+        std::thread tmpThread = std::thread(loop, threadOperations);
+        threads.push_back(move(tmpThread));
     }
 
     for (auto& th : threads) {
         th.join();
     }
 }
+
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+    gHasModifiedRefs = false;
+    ref = new RefBaseSubclass(&gRefDeleted, gRefDeletedLock);
+    weakRefs = ref->getWeakRefs();
+    // Since we are modifying flags, (flags & OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_WEAK
+    // is true. The destructor for RefBase should clean up weakrefs because of this.
     FuzzedDataProvider dataProvider(data, size);
     spawnThreads(&dataProvider);
+    LOG_ALWAYS_FATAL_IF(!gHasModifiedRefs && gRefDeleted, "ref(%p) was prematurely deleted!", ref);
+    // We need to explicitly delete this object
+    // if no refs have been added or deleted.
+    if (!gHasModifiedRefs && !gRefDeleted) {
+        delete ref;
+    }
+    LOG_ALWAYS_FATAL_IF(gHasModifiedRefs && !gRefDeleted,
+                        "ref(%p) should be deleted, is it leaking?", ref);
     return 0;
 }