Windows: buffer uninitialized if longer than 2^32 bytes

[josephlr]

The Windows implementation for getrandom_inner() calls RtlGenRandom. However, the length parameter is a ULONG (i.e. a u32).

Thus, if a buffer of length 2^32 is passed to getrandom() on Windows, the call dest.len() as ULONG truncates the value to 0. This results in the function seeming to succeed, but without writing any data.

Thanks to @briansmith's ring implementation, for pointing this out.

[dhardy]

So the ring implementation just truncates large requests to 4 GiB? We use .chunks_mut for several backends already, so should just to the same here.

[newpavlov]

Good catch! Yes, chunks_mut(u32::MAX) looks like a good solution.