From ac3cc33fee5e0f576cc9f04f7df40cd5d968be43 Mon Sep 17 00:00:00 2001 From: Oliver Middleton Date: Thu, 25 Feb 2016 01:35:41 +0000 Subject: [PATCH] rand: Fix filling buffers 4 GiB or larger with OsRng::fill_bytes on Windows CryptGenRandom takes a DWORD (u32) for the length so it only supports writing u32::MAX bytes at a time. Casting the length from a usize caused truncation meaning the whole buffer was not always filled. --- src/libstd/sys/windows/rand.rs | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/src/libstd/sys/windows/rand.rs b/src/libstd/sys/windows/rand.rs index fdd260b6e28..10e3d45f9d5 100644 --- a/src/libstd/sys/windows/rand.rs +++ b/src/libstd/sys/windows/rand.rs @@ -48,13 +48,17 @@ fn next_u64(&mut self) -> u64 { unsafe { mem::transmute(v) } } fn fill_bytes(&mut self, v: &mut [u8]) { - let ret = unsafe { - c::CryptGenRandom(self.hcryptprov, v.len() as c::DWORD, - v.as_mut_ptr()) - }; - if ret == 0 { - panic!("couldn't generate random bytes: {}", - io::Error::last_os_error()); + // CryptGenRandom takes a DWORD (u32) for the length so we need to + // split up the buffer. + for slice in v.chunks_mut(::max_value() as usize) { + let ret = unsafe { + c::CryptGenRandom(self.hcryptprov, slice.len() as c::DWORD, + slice.as_mut_ptr()) + }; + if ret == 0 { + panic!("couldn't generate random bytes: {}", + io::Error::last_os_error()); + } } } } -- 2.44.0