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References: <20190618093207.13436-1-ard.biesheuvel@linaro.org> <20190618093207.13436-2-ard.biesheuvel@linaro.org>
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From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 18 Jun 2019 02:39:04 -0700
Message-ID: <CANn89iJuTq36KMf1madQH08g6K0a-Uj-PDH80ao9zuEw+WNcZg@mail.gmail.com>
Subject: Re: [PATCH 1/2] net: fastopen: make key handling more robust against
 future changes
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     netdev <netdev@vger.kernel.org>,
        Eric Biggers <ebiggers@kernel.org>,
        linux-crypto@vger.kernel.org,
        Herbert Xu <herbert@gondor.apana.org.au>,
        David Miller <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jason Baron <jbaron@akamai.com>,
        Christoph Paasch <cpaasch@apple.com>,
        David Laight <David.Laight@aculab.com>,
        Yuchung Cheng <ycheng@google.com>
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On Tue, Jun 18, 2019 at 2:32 AM Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
>
> Some changes to the TCP fastopen code to make it more robust
> against future changes in the choice of key/cookie size, etc.
>
> - Instead of keeping the SipHash key in an untyped u8[] buffer
>   and casting it to the right type upon use, use the correct
>   siphash_key_t type directly. This ensures that the key will
>   appear at the correct alignment if we ever change the way
>   these data structures are allocated. (Currently, they are
>   only allocated via kmalloc so they always appear at the
>   correct alignment)
>
> - Use DIV_ROUND_UP when sizing the u64[] array to hold the
>   cookie, so it is always of sufficient size, even when
>   TCP_FASTOPEN_COOKIE_MAX is no longer a multiple of 8.
>
> - Add a key length check to tcp_fastopen_reset_cipher(). No
>   callers exist currently that fail this check (they all pass
>   compile constant values that equal TCP_FASTOPEN_KEY_LENGTH),
>   but future changes might create problems, e.g., by leaving part
>   of the key uninitialized, or overflowing the key buffers.
>
> Note that none of these are functional changes wrt the current
> state of the code.
>
...

> -       memcpy(ctx->key[0], primary_key, len);
> +       if (unlikely(len != TCP_FASTOPEN_KEY_LENGTH)) {
> +               pr_err("TCP: TFO key length %u invalid\n", len);
> +               err = -EINVAL;
> +               goto out;
> +       }


Why a pr_err() is there ?

Can unpriv users flood the syslog ?