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Add in a RtlGenRandom fallback for non-UWP Windows
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In some instances BCryptRandom will fail when RtlGenRandom will work.
On UWP, we might be unable to actually use RtlGenRandom.

Thread the needle and use RtlGenRandom when we have to, when we're able.

See also rust-lang/rust#108060

Fixes rust-random#314
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chutten committed Feb 22, 2023
1 parent 7c83ea0 commit 6609385
Showing 1 changed file with 17 additions and 0 deletions.
17 changes: 17 additions & 0 deletions src/windows.rs
Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,14 @@ extern "system" {
) -> u32;
}

// Forbidden when targetting UWP
#[cfg(not(target_vendor = "uwp"))]
#[link(name = "advapi32")]
extern "system" {
#[link_name = "SystemFunction036"]
fn RtlGenRandom(RandomBuffer: *mut c_void, RandomBufferLength: u32) -> u8;
}

pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
// Prevent overflow of u32
for chunk in dest.chunks_mut(u32::max_value() as usize) {
Expand All @@ -35,6 +43,15 @@ pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
};
// NTSTATUS codes use the two highest bits for severity status.
if ret >> 30 == 0b11 {
// Failed. Try RtlGenRandom as a fallback.
#[cfg(not(target_vendor = "uwp"))]
{
if unsafe { RtlGenRandom(chunk.as_mut_ptr() as *mut c_void, chunk.len() as u32) }
!= 0
{
continue;
}
}
// We zeroize the highest bit, so the error code will reside
// inside the range designated for OS codes.
let code = ret ^ (1 << 31);
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