This project might be open to known security vulnerabilities, which can be prevented by tightening the version range of affected dependencies. Find detailed information at the bottom.
maxminddb prior to version 0.27 declared Reader::open_mmap as safe
despite wrapping an inherently unsafe memmap2 operation with no
extra step done to guarantee safety. This could have led to undefined
behaviour if the file were to be modified on disk while the memory map
was still active.
In the unique reclaim path of BytesMut::reserve, the condition
if v_capacity >= new_cap + offset
uses an unchecked addition. When new_cap + offset overflows usize in release builds, this condition may incorrectly pass, causing self.cap to be set to a value that exceeds the actual allocated capacity. Subsequent APIs such as spare_capacity_mut() then trust this corrupted cap value and may create out-of-bounds slices, leading to UB.
This behavior is observable in release builds (integer overflow wraps), whereas debug builds panic due to overflow checks.
PoC
use bytes::*;
fn main() {
let mut a = BytesMut::from(&b"hello world"[..]);
let mut b = a.split_off(5);
// Ensure b becomes the unique owner of the backing storage
drop(a);
// Trigger overflow in new_cap + offset inside reserve
b.reserve(usize::MAX - 6);
// This call relies on the corrupted cap and may cause UB & HBO
b.put_u8(b'h');
}
Workarounds
Users of BytesMut::reserve are only affected if integer overflow checks are configured to wrap. When integer overflow is configured to panic, this issue does not apply.