Soundess bug: `&mut` reference exposes uninitialized bytes

[joshlf]

These lines in unsafe fn do_resolve convert a &mut [u8; _] to a &mut SYMBOL_INFOW:

backtrace-rs/src/symbolize/dbghelp.rs

Lines 226 to 227 in b65ab93

	let mut data = Aligned8([0u8; SIZE]);
	let info = unsafe { &mut *data.0.as_mut_ptr().cast::<SYMBOL_INFOW>() };

The SYMBOL_INFOW type has inter-field padding, which means that this &mut SYMBOL_INFOW could be used to write uninit bytes which would be exposed by the underlying [u8; _].

Note that the &mut SYMBOL_INFOW is passed to an external function:

backtrace-rs/src/symbolize/dbghelp.rs

Line 234 in b65ab93

if sym_from_addr(info) != TRUE {

sym_from_addr is an argument to this function:

backtrace-rs/src/symbolize/dbghelp.rs

Line 221 in b65ab93

sym_from_addr: impl FnOnce(*mut SYMBOL_INFOW) -> BOOL,

Any call to do_resolve which passes a sym_from_addr argument which writes to these padding locations would cause undefined behavior.

I would recommend modifying SYMBOL_INFOW with explicit padding fields to mitigate this problem.

[ChrisDenton]

The definitions are auto-generated from metadata using the windows-bindgen crate. Manually overwriting the implementation will just be overwritten on the next update.