From d53a5c4aa9051f2cca5407280fe53a09d67dfaad Mon Sep 17 00:00:00 2001 From: Michael Wachenschwanz Date: Fri, 17 Nov 2017 18:25:05 -0800 Subject: [PATCH] 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: I82de8eb5f5eb56f869542d5358e96884c24301b2 (cherry picked from commit c517681c66a1a387be657e0cf06da8d19659dd14) --- include/binder/Parcel.h | 2 ++ libs/binder/Parcel.cpp | 73 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 75 insertions(+) diff --git a/include/binder/Parcel.h b/include/binder/Parcel.h index 91ffae0ba..5d6f27f2c 100644 --- a/include/binder/Parcel.h +++ b/include/binder/Parcel.h @@ -247,6 +247,7 @@ private: void freeDataNoInit(); void initState(); void scanForFds() const; + status_t validateReadData(size_t len) const; template status_t readAligned(T *pArg) const; @@ -265,6 +266,7 @@ private: size_t mObjectsSize; size_t mObjectsCapacity; mutable size_t mNextObjectHint; + mutable bool mObjectsSorted; mutable bool mFdsKnown; mutable bool mHasFds; diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp index f474d9907..d121f78b7 100644 --- a/libs/binder/Parcel.cpp +++ b/libs/binder/Parcel.cpp @@ -464,6 +464,7 @@ void Parcel::setDataPosition(size_t pos) const mDataPos = pos; mNextObjectHint = 0; + mObjectsSorted = false; } status_t Parcel::setDataCapacity(size_t size) @@ -1133,6 +1134,59 @@ 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) { @@ -1143,6 +1197,10 @@ 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); @@ -1161,6 +1219,11 @@ 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); @@ -1174,6 +1237,11 @@ 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(data); @@ -1638,6 +1706,7 @@ void Parcel::ipcSetDataReference(const uint8_t* data, size_t dataSize, mObjects = const_cast(objects); mObjectsSize = mObjectsCapacity = objectsCount; mNextObjectHint = 0; + mObjectsSorted = false; mOwner = relFunc; mOwnerCookie = relCookie; for (size_t i = 0; i < mObjectsSize; i++) { @@ -1795,6 +1864,7 @@ status_t Parcel::restartWrite(size_t desired) mObjects = NULL; mObjectsSize = mObjectsCapacity = 0; mNextObjectHint = 0; + mObjectsSorted = false; mHasFds = false; mFdsKnown = true; mAllowFds = true; @@ -1881,6 +1951,7 @@ status_t Parcel::continueWrite(size_t desired) mDataCapacity = desired; mObjectsSize = mObjectsCapacity = objectsSize; mNextObjectHint = 0; + mObjectsSorted = false; } else if (mData) { if (objectsSize < mObjectsSize) { @@ -1906,6 +1977,7 @@ status_t Parcel::continueWrite(size_t desired) } mObjectsSize = objectsSize; mNextObjectHint = 0; + mObjectsSorted = false; } // We own the data, so we can just do a realloc(). @@ -1978,6 +2050,7 @@ void Parcel::initState() mObjectsSize = 0; mObjectsCapacity = 0; mNextObjectHint = 0; + mObjectsSorted = false; mHasFds = false; mFdsKnown = true; mAllowFds = true;