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Avoid panicking when Windows memory is already unlocked #22

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Avoid panicking when Windows memory is already unlocked #22

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19 changes: 16 additions & 3 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -101,9 +101,12 @@ impl<S: Zeroize> Drop for SecretBox<S> {

#[cfg(windows)]
unsafe {
if windows_sys::Win32::System::Memory::VirtualUnlock(secret_ptr.cast(), len) == 0 {
panic!("VirtualUnlock failed",);
}
// VirtualLock does not maintain a lock count for overlapping pages.
// Heap allocations commonly share pages, so dropping one SecretBox
// can unlock a page that still contains another SecretBox. A later
// VirtualUnlock then reports ERROR_NOT_LOCKED. Drop must still
// zeroize the secret and must never panic while unwinding.
let _ = windows_sys::Win32::System::Memory::VirtualUnlock(secret_ptr.cast(), len);
}

self.zeroize()
Expand Down Expand Up @@ -363,6 +366,16 @@ mod tests {
assert!(TestSecret::default().check_zero());
}

#[cfg(windows)]
#[test]
fn dropping_multiple_secrets_does_not_panic() {
let secrets = (0..64)
.map(|index| SecretString::new(Box::new(format!("secret-{index}"))))
.collect::<Vec<_>>();

drop(secrets);
}

#[test]
fn test_secret_box_expose_secret_mut() {
let secret = Box::new(String::from("Encrypted"));
Expand Down