reading on uninitialized memory may cause undefined behavior

[JOE1994]

Hello 🦀 ,
we (Rust group @sslab-gatech) found a memory-safety/soundness issue in this crate while scanning Rust code on crates.io for potential vulnerabilities.

Issue Description

csv-sniffer/src/snip.rs

Lines 7 to 18 in d964e42

	pub(crate) fn preamble_skipcount<R: Read>(reader: &mut R, n_preamble_rows: usize)
	-> Result<usize>
	{
	if n_preamble_rows == 0 {
	return Ok(0);
	}
	let mut skipcount = 0;
	loop {
	let cap = 1 << 12;
	let mut buffer = Vec::with_capacity(cap);
	unsafe { buffer.set_len(cap); }
	let n_read = reader.read(&mut buffer)?;

preamble_skipcount method creates an uninitialized buffer (buffer) and passes it to user-provided Read implementation. This is unsound, because it allows safe Rust code to exhibit an undefined behavior (read from uninitialized memory).

This part from the Read trait documentation explains the issue:

It is your responsibility to make sure that buf is initialized before calling read. Calling read with an uninitialized buf (of the kind one obtains via MaybeUninit<T>) is not safe, and can lead to undefined behavior.

Suggested Fix

It is safe to zero-initialize the newly allocated u8 buffer before read(), in order to prevent user-provided Read from accessing old contents of the newly allocated heap memory.

Thank you for checking out this issue 👍

[jblondin]

Fixed by #2