Sanitize InputMessage before sending

The struct InputMessage has many fields, and is force-aligned to 8-byte
boundaries. There are also some padding fields that carry no
information.

This struct is typically allocated in the stack and populated with
various values before being sent across as a stream of bytes through the
socket.

Therefore, the "unused" data portions of the struct could contain
portions of the stack, since there aren't ever writes to those memory
locations.

To avoid this information leak, forcefully sanitize the struct. Create a
new struct that is explicitly set to zero. Next, only fill the
meaningful fields manually.

Bug: 115739809
Test: cts-tradefed run cts -m CtsSecurityBulletinHostTestCases -t android.security.cts.Poc18_12; adb shell monkey 100000
Change-Id: I7e44dacf1e8fa3156c8e4d2f7784ef0c53dab507
Merged-In: I7e44dacf1e8fa3156c8e4d2f7784ef0c53dab507

1 files changed, 13 insertions, 0 deletions

diff --git a/include/input/InputTransport.h b/include/input/InputTransport.h
index ea1d2aa41f..9f3d45a3bc 100644
--- a/include/input/InputTransport.h
+++ b/include/input/InputTransport.h
@@ -42,6 +42,13 @@ namespace android {
  *
  * Note that this structure is used for IPCs so its layout must be identical
  * on 64 and 32 bit processes. This is tested in StructLayout_test.cpp.
+ *
+ * Since the struct must be aligned to an 8-byte boundary, there could be uninitialized bytes
+ * in-between the defined fields. This padding data should be explicitly accounted for by adding
+ * "empty" fields into the struct. This data is memset to zero before sending the struct across
+ * the socket. Adding the explicit fields ensures that the memset is not optimized away by the
+ * compiler. When a new field is added to the struct, the corresponding change
+ * in StructLayout_test should be made.
  */
 struct InputMessage {
     enum {
@@ -62,6 +69,7 @@ struct InputMessage {
     union Body {
         struct Key {
             uint32_t seq;
+            uint32_t empty1;
             nsecs_t eventTime __attribute__((aligned(8)));
             int32_t deviceId;
             int32_t source;
@@ -72,6 +80,7 @@ struct InputMessage {
             int32_t scanCode;
             int32_t metaState;
             int32_t repeatCount;
+            uint32_t empty2;
             nsecs_t downTime __attribute__((aligned(8)));
 
             inline size_t size() const {
@@ -81,6 +90,7 @@ struct InputMessage {
 
         struct Motion {
             uint32_t seq;
+            uint32_t empty1;
             nsecs_t eventTime __attribute__((aligned(8)));
             int32_t deviceId;
             int32_t source;
@@ -91,12 +101,14 @@ struct InputMessage {
             int32_t metaState;
             int32_t buttonState;
             int32_t edgeFlags;
+            uint32_t empty2;
             nsecs_t downTime __attribute__((aligned(8)));
             float xOffset;
             float yOffset;
             float xPrecision;
             float yPrecision;
             uint32_t pointerCount;
+            uint32_t empty3;
             // Note that PointerCoords requires 8 byte alignment.
             struct Pointer {
                 PointerProperties properties;
@@ -127,6 +139,7 @@ struct InputMessage {
 
     bool isValid(size_t actualSize) const;
     size_t size() const;
+    void getSanitizedCopy(InputMessage* msg) const;
 };
 
 /*