Fix CryptoPlugin use after free vulnerability.

The shared memory buffer used by srcPtr can be freed by another
thread because it is not protected by a mutex. Subsequently,
a use after free AIGABRT can occur in a race condition.

SafetyNet logging is not added to avoid log spamming. The
mutex lock is called to setup for decryption, which is
called frequently.

The crash was reproduced on the device before the fix.
Verified the test passes after the fix.

Test: sts
  sts-tradefed run sts-engbuild-no-spl-lock -m StsHostTestCases --test android.security.sts.Bug_176495665#testPocBug_176495665

Test: push to device with target_hwasan-userdebug build
  adb shell /data/local/tmp/Bug-176495665_sts64

Bug: 176495665
Bug: 176444161
Change-Id: I4c83c44873eef960b654f387a3574fcad49c41a9

1 files changed, 8 insertions, 2 deletions

diff --git a/drm/1.0/default/CryptoPlugin.cpp b/drm/1.0/default/CryptoPlugin.cpp
index e6d4e8447b..de8bbd599c 100644
--- a/drm/1.0/default/CryptoPlugin.cpp
+++ b/drm/1.0/default/CryptoPlugin.cpp
@@ -53,6 +53,8 @@ namespace implementation {
             uint32_t bufferId) {
         sp<IMemory> hidlMemory = mapMemory(base);
 
+        std::lock_guard<std::mutex> shared_buffer_lock(mSharedBufferLock);
+
         // allow mapMemory to return nullptr
         mSharedBufferMap[bufferId] = hidlMemory;
         return Void();
@@ -65,7 +67,7 @@ namespace implementation {
             const SharedBuffer& source, uint64_t offset,
             const DestinationBuffer& destination,
             decrypt_cb _hidl_cb) {
-
+        std::unique_lock<std::mutex> shared_buffer_lock(mSharedBufferLock);
         if (mSharedBufferMap.find(source.bufferId) == mSharedBufferMap.end()) {
             _hidl_cb(Status::ERROR_DRM_CANNOT_HANDLE, 0, "source decrypt buffer base not set");
             return Void();
@@ -79,7 +81,7 @@ namespace implementation {
             }
         }
 
-        android::CryptoPlugin::Mode legacyMode;
+        android::CryptoPlugin::Mode legacyMode = android::CryptoPlugin::kMode_Unencrypted;
         switch(mode) {
         case Mode::UNENCRYPTED:
             legacyMode = android::CryptoPlugin::kMode_Unencrypted;
@@ -170,6 +172,10 @@ namespace implementation {
             _hidl_cb(Status::BAD_VALUE, 0, "invalid destination type");
             return Void();
         }
+
+        // release mSharedBufferLock
+        shared_buffer_lock.unlock();
+
         ssize_t result = mLegacyPlugin->decrypt(secure, keyId.data(), iv.data(),
                 legacyMode, legacyPattern, srcPtr, legacySubSamples.get(),
                 subSamples.size(), destPtr, &detailMessage);