netdev - Re: [PATCH net-next] tcp-zerocopy: Update returned getsockopt() optlen.

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Message-ID: <CANn89iLrOwvNSHOB2i_+gMmN29O6BpJrnd9RfNERDTayNf7qKA@mail.gmail.com>
Date:   Mon, 24 Feb 2020 22:28:22 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Arjun Roy <arjunroy.kdev@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>, Arjun Roy <arjunroy@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] tcp-zerocopy: Update returned getsockopt() optlen.

On Mon, Feb 24, 2020 at 10:06 PM Arjun Roy <arjunroy.kdev@...il.com> wrote:
>
> From: Arjun Roy <arjunroy@...gle.com>
>
> TCP receive zerocopy currently does not update the returned optlen for
> getsockopt(). Thus, userspace cannot properly determine if all the
> fields are set in the passed-in struct. This patch sets the optlen
> before return, in keeping with the expected operation of getsockopt().
>
> Signed-off-by: Arjun Roy <arjunroy@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> Fixes: c8856c051454 ("tcp-zerocopy: Return inq along with tcp receive
> zerocopy")


OK, please note for next time :

Fixes: tag should not wrap : It should be a single line.
Preferably it should be the first tag (before your Sob)

Add v2 as in [PATCH v2 net-next]  :  so that reviewers can easily see
which version is the more recent one.


>
> +               if (!err) {
> +                       if (put_user(len, optlen))
> +                               return -EFAULT;

Sorry for not asking this before during our internal review :

Is the cost of the extra STAC / CLAC (on x86) being high enough that it is worth
trying to call put_user() only if user provided a different length ?