netdev - Re: [net v2] tcp: Specify cmsgbuf is user pointer for receive zerocopy.

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Message-ID: <CANn89iJeEKGDeOSz2OuZ4feZBFWf5A20Ab3gQ9q5VshRzSzZnA@mail.gmail.com>
Date:   Thu, 6 May 2021 21:17:32 +0200
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>
Subject: Re: [net v2] tcp: Specify cmsgbuf is user pointer for receive zerocopy.

On Thu, May 6, 2021 at 9:06 PM Arjun Roy <arjunroy.kdev@...il.com> wrote:
>
> From: Arjun Roy <arjunroy@...gle.com>
>
> A prior change (1f466e1f15cf) introduces separate handling for
> ->msg_control depending on whether the pointer is a kernel or user
> pointer. However, while tcp receive zerocopy is using this field, it
> is not properly annotating that the buffer in this case is a user
> pointer. This can cause faults when the improper mechanism is used
> within put_cmsg().
>
> This patch simply annotates tcp receive zerocopy's use as explicitly
> being a user pointer.
>
> Fixes: 7eeba1706eba ("tcp: Add receive timestamp support for receive zerocopy.")
> Signed-off-by: Arjun Roy <arjunroy@...gle.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>


> ---
>
> Changelog since v1:
> - Updated "Fixes" tag and commit message to properly account for which
>   commit introduced buggy behaviour.
>
>  net/ipv4/tcp.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index e14fd0c50c10..f1c1f9e3de72 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2039,6 +2039,7 @@ static void tcp_zc_finalize_rx_tstamp(struct sock *sk,
>                 (__kernel_size_t)zc->msg_controllen;
>         cmsg_dummy.msg_flags = in_compat_syscall()
>                 ? MSG_CMSG_COMPAT : 0;
> +       cmsg_dummy.msg_control_is_user = true;
>         zc->msg_flags = 0;
>         if (zc->msg_control == msg_control_addr &&
>             zc->msg_controllen == cmsg_dummy.msg_controllen) {
> --
> 2.31.1.607.g51e8a6a459-goog
>