Fix out-of-bounds memory write in

Windows x64 uses the IL32P64 data model, which means that unsigned int
is 32 bits and size_t is 64 bits. Previously, the expression
|~(alignment - 1)| resulted in the 32-bit value 0xFFFFFFF0, which was
then extended to the 64-bit value 0x00000000FFFFFFF0 when promoted to
size_t. When the input pointer was masked with this value, the result
was a pointer that was usually way outside the boundaries of the array.

The new code casts |alignment| to size_t first prior to the bitwise
negation, resulting in the correct mask value of 0xFFFFFFFFFFFFFFF0.

Change-Id: I04754aa9e1ce7a615c2b4c74051cfcca38dbb52f
Reviewed-by: Adam Langley <>
1 file changed