netdev - Re: [PATCH 0/6] Constant Time Memory Comparisons Are Important

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Date:   Sun, 11 Jun 2017 23:30:33 +0200
From:   Emil Lenngren <emil.lenngren@...il.com>
To:     Emmanuel Grumbach <egrumbach@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        David Howells <dhowells@...hat.com>,
        David Safford <safford@...ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Gilad Ben-Yossef <gilad@...yossef.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Johannes Berg <johannes@...solutions.net>,
        Marcel Holtmann <marcel@...tmann.org>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        keyrings@...r.kernel.org,
        Bluez mailing list <linux-bluetooth@...r.kernel.org>,
        "open list:NFS, SUNRPC, AND..." <linux-nfs@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH 0/6] Constant Time Memory Comparisons Are Important

2017-06-11 22:48 GMT+02:00 Emmanuel Grumbach <egrumbach@...il.com>:
> On Sun, Jun 11, 2017 at 4:36 PM, Kees Cook <keescook@...omium.org> wrote:
>>
>> On Sun, Jun 11, 2017 at 1:13 AM, Kalle Valo <kvalo@...eaurora.org> wrote:
>> > "Jason A. Donenfeld" <Jason@...c4.com> writes:
>> >
>> >> Whenever you're comparing two MACs, it's important to do this using
>> >> crypto_memneq instead of memcmp. With memcmp, you leak timing information,
>> >> which could then be used to iteratively forge a MAC.
>> >
>> > Do you have any pointers where I could learn more about this?
>>
>> While not using C specifically, this talks about the problem generally:
>> https://www.chosenplaintext.ca/articles/beginners-guide-constant-time-cryptography.html
>>
>
> Sorry for the stupid question, but the MAC address is in plaintext in
> the air anyway or easily accessible via user space tools. I fail to
> see what it is so secret about a MAC address in that code where that
> same MAC address is accessible via myriads of ways.

I think you're mixing up Media Access Control (MAC) addresses with
Message Authentication Code (MAC). The second one is a cryptographic
signature of a message.