Fix WasmPtr to work with accesses accessing the final valid byte #1272
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This also returns `None` for all accesses of zero sized types and arrays of length 0. Because the array accesses have a non-inclusive length, length of 0 is not valid. These checks prevent returning empty slices that point just outside of memory bounds.
MarkMcCaskey
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syrusakbary
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Resolves #1258
The fix was to change
>=into>. Doing this made us vulnerable to accessing memory to create an empty slice just out of bounds so we have to add some additional checks to make sure that that can't happen.This PR also prevents accessing arrays of length 0 (the length bound is non-inclusive, so length 0 is never valid) and prevents access of zero-sized types.
The zero-sized type checks will probably be inlined (or will be in the future as
const fngets more mature) so provide no additional overhead. The checking of if length == 0 does add some overhead, but on modern CPUs it shouldn't be an issue as it's a branch that should be always false in normal use.Review