Check bounds in offsetToPtr

Check whether specified offset belongs to mData.
Also added a default argument bufferSize to check the end offset.

Size of the ashmem descriptor can be modified between
ashmem_get_size_region call and mmap. createFromParcel method was updated
to check ashmem size again immediately after memory is mapped.

Test: manual - using the test app from the bug
Bug: 34128677
Change-Id: I3ecd1616a870ce20941ce9b20a1843d2b4295750

libs/androidfw/CursorWindow.cpp

@@ -98,9 +98,14 @@ status_t CursorWindow::createFromParcel(Parcel* parcel, CursorWindow** outCursor
             if (dupAshmemFd < 0) {
                 result = -errno;
             } else {
+                // the size of the ashmem descriptor can be modified between ashmem_get_size_region
+                // call and mmap, so we'll check again immediately after memory is mapped
                 void* data = ::mmap(NULL, size, PROT_READ, MAP_SHARED, dupAshmemFd, 0);
                 if (data == MAP_FAILED) {
                     result = -errno;
+                } else if (ashmem_get_size_region(dupAshmemFd) != size) {
+                    ::munmap(data, size);
+                    result = BAD_VALUE;
                 } else {
                     CursorWindow* window = new CursorWindow(name, dupAshmemFd,
                             data, size, true /*readOnly*/);

libs/androidfw/include/androidfw/CursorWindow.h

@@ -17,6 +17,7 @@
 #ifndef _ANDROID__DATABASE_WINDOW_H
 #define _ANDROID__DATABASE_WINDOW_H
 
+#include <inttypes.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ -128,12 +129,13 @@ class CursorWindow {
     inline const char* getFieldSlotValueString(FieldSlot* fieldSlot,
             size_t* outSizeIncludingNull) {
         *outSizeIncludingNull = fieldSlot->data.buffer.size;
-        return static_cast<char*>(offsetToPtr(fieldSlot->data.buffer.offset));
+        return static_cast<char*>(offsetToPtr(
+                fieldSlot->data.buffer.offset, fieldSlot->data.buffer.size));
     }
 
     inline const void* getFieldSlotValueBlob(FieldSlot* fieldSlot, size_t* outSize) {
         *outSize = fieldSlot->data.buffer.size;
-        return offsetToPtr(fieldSlot->data.buffer.offset);
+        return offsetToPtr(fieldSlot->data.buffer.offset, fieldSlot->data.buffer.size);
     }
 
 private:
@@ -166,7 +168,16 @@ class CursorWindow {
     bool mReadOnly;
     Header* mHeader;
 
-    inline void* offsetToPtr(uint32_t offset) {
+    inline void* offsetToPtr(uint32_t offset, uint32_t bufferSize = 0) {
+        if (offset >= mSize) {
+            ALOGE("Offset %" PRIu32 " out of bounds, max value %zu", offset, mSize);
+            return NULL;
+        }
+        if (offset + bufferSize > mSize) {
+            ALOGE("End offset %" PRIu32 " out of bounds, max value %zu",
+                    offset + bufferSize, mSize);
+            return NULL;
+        }
         return static_cast<uint8_t*>(mData) + offset;
     }