Check mDataPos to see if the Parcel needs to grow

Flag: EXEMPT bug fix
Ignore-AOSP-First: security fix
Test: atest binderUnitTest
Bug: 399155883
Change-Id: I38b755ca3381cfca3300292873f763823fbf169b

Author: devinmoore-goog

libs/binder/Parcel.cpp

@@ -542,7 +542,7 @@ status_t Parcel::appendFrom(const Parcel* parcel, size_t offset, size_t len) {
         return BAD_VALUE;
     }
 
-    if ((mDataSize+len) > mDataCapacity) {
+    if ((mDataPos + len) > mDataCapacity) {
         // grow data
         err = growData(len);
         if (err != NO_ERROR) {

libs/binder/tests/binderParcelUnitTest.cpp

@@ -197,6 +197,17 @@ TEST(Parcel, AppendPlainDataPartial) {
     ASSERT_EQ(2, p2.readInt32());
 }
 
+TEST(Parcel, AppendWithBadDataPos) {
+    Parcel p1;
+    p1.writeInt32(1);
+    p1.writeInt32(1);
+    Parcel p2;
+    p2.setDataCapacity(8);
+    p2.setDataPosition(10000);
+
+    EXPECT_EQ(android::BAD_VALUE, p2.appendFrom(&p1, 0, 8));
+}
+
 TEST(Parcel, HasBinders) {
     sp<IBinder> b1 = sp<BBinder>::make();