From ff537c8516e1f8be96264d3c5db3ac084e307566 Mon Sep 17 00:00:00 2001
From: Edwin Wong <edwinwong@google.com>
Date: Tue, 2 Feb 2021 10:42:38 -0800
Subject: [PATCH] [RESTRICT AUTOMERGE] Fix potential decrypt destPtr overflow.

There is a potential integer overflow to bypass the
destination base size check in decrypt. The destPtr
can then point to the outside of the destination buffer.

Test: sts-tradefed
  sts-tradefed run sts-engbuild-no-spl-lock -m StsHostTestCases --test android.security.sts.Bug_176444622#testPocBug_176444622

Test: push to device with target_hwasan-userdebug build
  adb shell /data/local/tmp/Bug-17644462264

Bug: 176444622
Bug: 176496353
Change-Id: I71b390846a17aecbb9180865e1f9538b4b464abf
---
 drm/1.0/default/CryptoPlugin.cpp | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drm/1.0/default/CryptoPlugin.cpp b/drm/1.0/default/CryptoPlugin.cpp
index e60ba8f54d..e71385da5d 100644
--- a/drm/1.0/default/CryptoPlugin.cpp
+++ b/drm/1.0/default/CryptoPlugin.cpp
@@ -80,7 +80,7 @@ namespace implementation {
             }
         }
 
-        android::CryptoPlugin::Mode legacyMode;
+        android::CryptoPlugin::Mode legacyMode = android::CryptoPlugin::kMode_Unencrypted;
         switch(mode) {
         case Mode::UNENCRYPTED:
             legacyMode = android::CryptoPlugin::kMode_Unencrypted;
@@ -147,7 +147,10 @@ namespace implementation {
                 return Void();
             }
 
-            if (destBuffer.offset + destBuffer.size > destBase->getSize()) {
+            size_t totalDstSize = 0;
+            if (__builtin_add_overflow(destBuffer.offset, destBuffer.size, &totalDstSize) ||
+                totalDstSize > destBase->getSize()) {
+                android_errorWriteLog(0x534e4554, "176496353");
                 _hidl_cb(Status::ERROR_DRM_CANNOT_HANDLE, 0, "invalid buffer size");
                 return Void();
             }
@@ -158,7 +161,7 @@ namespace implementation {
             }
 
             base = static_cast<uint8_t *>(static_cast<void *>(destBase->getPointer()));
-            destPtr = static_cast<void *>(base + destination.nonsecureMemory.offset);
+            destPtr = static_cast<void*>(base + destination.nonsecureMemory.offset);
         } else if (destination.type == BufferType::NATIVE_HANDLE) {
             if (!secure) {
                 _hidl_cb(Status::BAD_VALUE, 0, "native handle destination must be secure");