Disallow reading object data from Parcels with non-object reads

The check added to each non-object reads adds an overhead. If the
objects (binders and file descriptors) were written to the Parcel in
sequential order then check adds a small O(1) overhead to each read,
plus an O(N) overhead to the first read (to verify the N objects were
added in order).
If the objects were written out of order (as in by jumping around the Parcel
with setDataPosition and writing Binder, DON'T DO THIS!!) (writing non
objects out of order is fine), the first read is forced to sort the objects
in the internal bookkeeping. Based on the assumption non sequential writes
are infrequent and overall Parcels are probably mostly sorted, insertion
sort was used. Worst case sorts will add an O(N^2) overhead to the first
non object read from the Parcel.

Test: run cts -m CtsOsTestCases -t android.os.cts.ParcelTest

Bug: 29833520
Change-Id: Id0119caf530023fe8b61be6d15f5b6a9c49c08df
Merged-In: I82de8eb5f5eb56f869542d5358e96884c24301b2

1 files changed, 73 insertions, 0 deletions

diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index cfcf73b8d6..ef14475ae2 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -396,6 +396,7 @@ void Parcel::setDataPosition(size_t pos) const
 
     mDataPos = pos;
     mNextObjectHint = 0;
+    mObjectsSorted = false;
 }
 
 status_t Parcel::setDataCapacity(size_t size)
@@ -1059,6 +1060,59 @@ void Parcel::remove(size_t /*start*/, size_t /*amt*/)
     LOG_ALWAYS_FATAL("Parcel::remove() not yet implemented!");
 }
 
+status_t Parcel::validateReadData(size_t upperBound) const
+{
+    // Don't allow non-object reads on object data
+    if (mObjectsSorted || mObjectsSize <= 1) {
+data_sorted:
+        // Expect to check only against the next object
+        if (mNextObjectHint < mObjectsSize && upperBound > mObjects[mNextObjectHint]) {
+            // For some reason the current read position is greater than the next object
+            // hint. Iterate until we find the right object
+            size_t nextObject = mNextObjectHint;
+            do {
+                if (mDataPos < mObjects[nextObject] + sizeof(flat_binder_object)) {
+                    // Requested info overlaps with an object
+                    ALOGE("Attempt to read from protected data in Parcel %p", this);
+                    return PERMISSION_DENIED;
+                }
+                nextObject++;
+            } while (nextObject < mObjectsSize && upperBound > mObjects[nextObject]);
+            mNextObjectHint = nextObject;
+        }
+        return NO_ERROR;
+    }
+    // Quickly determine if mObjects is sorted.
+    binder_size_t* currObj = mObjects + mObjectsSize - 1;
+    binder_size_t* prevObj = currObj;
+    while (currObj > mObjects) {
+        prevObj--;
+        if(*prevObj > *currObj) {
+            goto data_unsorted;
+        }
+        currObj--;
+    }
+    mObjectsSorted = true;
+    goto data_sorted;
+
+data_unsorted:
+    // Insertion Sort mObjects
+    // Great for mostly sorted lists. If randomly sorted or reverse ordered mObjects become common,
+    // switch to std::sort(mObjects, mObjects + mObjectsSize);
+    for (binder_size_t* iter0 = mObjects + 1; iter0 < mObjects + mObjectsSize; iter0++) {
+        binder_size_t temp = *iter0;
+        binder_size_t* iter1 = iter0 - 1;
+        while (iter1 >= mObjects && *iter1 > temp) {
+            *(iter1 + 1) = *iter1;
+            iter1--;
+        }
+        *(iter1 + 1) = temp;
+    }
+    mNextObjectHint = 0;
+    mObjectsSorted = true;
+    goto data_sorted;
+}
+
 status_t Parcel::read(void* outData, size_t len) const
 {
     if (len > INT32_MAX) {
@@ -1069,6 +1123,10 @@ status_t Parcel::read(void* outData, size_t len) const
 
     if ((mDataPos+pad_size(len)) >= mDataPos && (mDataPos+pad_size(len)) <= mDataSize
             && len <= pad_size(len)) {
+        if (mObjectsSize > 0) {
+            status_t err = validateReadData(mDataPos + pad_size(len));
+            if(err != NO_ERROR) return err;
+        }
         memcpy(outData, mData+mDataPos, len);
         mDataPos += pad_size(len);
         ALOGV("read Setting data pos of %p to %zu", this, mDataPos);
@@ -1087,6 +1145,11 @@ const void* Parcel::readInplace(size_t len) const
 
     if ((mDataPos+pad_size(len)) >= mDataPos && (mDataPos+pad_size(len)) <= mDataSize
             && len <= pad_size(len)) {
+        if (mObjectsSize > 0) {
+            status_t err = validateReadData(mDataPos + pad_size(len));
+            if(err != NO_ERROR) return NULL;
+        }
+
         const void* data = mData+mDataPos;
         mDataPos += pad_size(len);
         ALOGV("readInplace Setting data pos of %p to %zu", this, mDataPos);
@@ -1100,6 +1163,11 @@ status_t Parcel::readAligned(T *pArg) const {
     COMPILE_TIME_ASSERT_FUNCTION_SCOPE(PAD_SIZE_UNSAFE(sizeof(T)) == sizeof(T));
 
     if ((mDataPos+sizeof(T)) <= mDataSize) {
+        if (mObjectsSize > 0) {
+            status_t err = validateReadData(mDataPos + sizeof(T));
+            if(err != NO_ERROR) return err;
+        }
+
         const void* data = mData+mDataPos;
         mDataPos += sizeof(T);
         *pArg =  *reinterpret_cast<const T*>(data);
@@ -1564,6 +1632,7 @@ void Parcel::ipcSetDataReference(const uint8_t* data, size_t dataSize,
     mObjects = const_cast<binder_size_t*>(objects);
     mObjectsSize = mObjectsCapacity = objectsCount;
     mNextObjectHint = 0;
+    mObjectsSorted = false;
     mOwner = relFunc;
     mOwnerCookie = relCookie;
     for (size_t i = 0; i < mObjectsSize; i++) {
@@ -1713,6 +1782,7 @@ status_t Parcel::restartWrite(size_t desired)
     mObjects = NULL;
     mObjectsSize = mObjectsCapacity = 0;
     mNextObjectHint = 0;
+    mObjectsSorted = false;
     mHasFds = false;
     mFdsKnown = true;
     mAllowFds = true;
@@ -1799,6 +1869,7 @@ status_t Parcel::continueWrite(size_t desired)
         mDataCapacity = desired;
         mObjectsSize = mObjectsCapacity = objectsSize;
         mNextObjectHint = 0;
+        mObjectsSorted = false;
 
     } else if (mData) {
         if (objectsSize < mObjectsSize) {
@@ -1820,6 +1891,7 @@ status_t Parcel::continueWrite(size_t desired)
             }
             mObjectsSize = objectsSize;
             mNextObjectHint = 0;
+            mObjectsSorted = false;
         }
 
         // We own the data, so we can just do a realloc().
@@ -1892,6 +1964,7 @@ void Parcel::initState()
     mObjectsSize = 0;
     mObjectsCapacity = 0;
     mNextObjectHint = 0;
+    mObjectsSorted = false;
     mHasFds = false;
     mFdsKnown = true;
     mAllowFds = true;