linux-kernel - Re: net/dev: fix information leak to userspace

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Message-ID: <CAM_iQpWb_s_rPzi-i=Fhgk4xCPSY7N8FBjt_p_6qoZLr5HgAwA@mail.gmail.com>
Date:   Sun, 21 Mar 2021 18:07:37 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Pavel Machek <pavel@...x.de>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        Eric Dumazet <edumazet@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        Cong Wang <cong.wang@...edance.com>,
        Taehee Yoo <ap420073@...il.com>,
        Björn Töpel <bjorn@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: net/dev: fix information leak to userspace

On Sun, Mar 21, 2021 at 9:34 AM Pavel Machek <pavel@...x.de> wrote:
>
> dev_get_mac_address() does not always initialize whole
> structure. Unfortunately, other code copies such structure to
> userspace, leaking information. Fix it.

Well, most callers already initialize it with a memset() or copy_from_user(),
for example, __tun_chr_ioctl():

        if (cmd == TUNSETIFF || cmd == TUNSETQUEUE ||
            (_IOC_TYPE(cmd) == SOCK_IOC_TYPE && cmd != SIOCGSKNS)) {
                if (copy_from_user(&ifr, argp, ifreq_len))
                        return -EFAULT;
        } else {
                memset(&ifr, 0, sizeof(ifr));
        }

Except tap_ioctl(), but we can just initialize 'sa' there instead of doing
it in dev_get_mac_address().

Thanks.