Sanity check IMemory access versus underlying mmap

Bug 26877992

Change-Id: Ibbf4b1061e4675e4e96bc944a865b53eaf6984fe
(cherry picked from commit 94b0d4e)

Author: Christopher Tate

libs/binder/IMemory.cpp

@@ -26,6 +26,7 @@
 #include <sys/mman.h>
 
 #include <binder/IMemory.h>
+#include <cutils/log.h>
 #include <utils/KeyedVector.h>
 #include <utils/threads.h>
 #include <utils/Atomic.h>
@@ -187,15 +188,26 @@ sp<IMemoryHeap> BpMemory::getMemory(ssize_t* offset, size_t* size) const
             if (heap != 0) {
                 mHeap = interface_cast<IMemoryHeap>(heap);
                 if (mHeap != 0) {
-                    mOffset = o;
-                    mSize = s;
+                    size_t heapSize = mHeap->getSize();
+                    if (s <= heapSize
+                            && o >= 0
+                            && (static_cast<size_t>(o) <= heapSize - s)) {
+                        mOffset = o;
+                        mSize = s;
+                    } else {
+                        // Hm.
+                        android_errorWriteWithInfoLog(0x534e4554,
+                            "26877992", -1, NULL, 0);
+                        mOffset = 0;
+                        mSize = 0;
+                    }
                 }
             }
         }
     }
     if (offset) *offset = mOffset;
     if (size) *size = mSize;
-    return mHeap;
+    return (mSize > 0) ? mHeap : 0;
 }
 
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