netdev - Re: [PATCH v3] tcp: verify the checksum of the first data segment in a new connection

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Date:   Wed, 13 Jun 2018 15:10:01 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     Frank van der Linden <fllinden@...zon.com>
Cc:     edumazet@...gle.com, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v3] tcp: verify the checksum of the first data segment in
 a new connection

On Wed, Jun 13, 2018 at 9:09 AM, Frank van der Linden
<fllinden@...zon.com> wrote:
> commit 079096f103fa ("tcp/dccp: install syn_recv requests into ehash
> table") introduced an optimization for the handling of child sockets
> created for a new TCP connection.
>
> But this optimization passes any data associated with the last ACK of the
> connection handshake up the stack without verifying its checksum, because it
> calls tcp_child_process(), which in turn calls tcp_rcv_state_process()
> directly.  These lower-level processing functions do not do any checksum
> verification.
>
> Insert a tcp_checksum_complete call in the TCP_NEW_SYN_RECEIVE path to
> fix this.
>
> Signed-off-by: Frank van der Linden <fllinden@...zon.com>
> ---
>  net/ipv4/tcp_ipv4.c | 4 ++++
>  net/ipv6/tcp_ipv6.c | 4 ++++
>  2 files changed, 8 insertions(+)
>
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index f70586b..ef8cd0f 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1689,6 +1689,10 @@ int tcp_v4_rcv(struct sk_buff *skb)
>                         reqsk_put(req);
>                         goto discard_it;
>                 }
> +               if (tcp_checksum_complete(skb)) {
> +                       reqsk_put(req);
> +                       goto csum_error;
> +               }
>                 if (unlikely(sk->sk_state != TCP_LISTEN)) {
>                         inet_csk_reqsk_queue_drop_and_put(sk, req);
>                         goto lookup;
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 6d664d8..5d4eb9d 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1475,6 +1475,10 @@ static int tcp_v6_rcv(struct sk_buff *skb)
>                         reqsk_put(req);
>                         goto discard_it;
>                 }
> +               if (tcp_checksum_complete(skb)) {
> +                       reqsk_put(req);
> +                       goto csum_error;
> +               }
>                 if (unlikely(sk->sk_state != TCP_LISTEN)) {
>                         inet_csk_reqsk_queue_drop_and_put(sk, req);
>                         goto lookup;


I've tested the IPv4 variant with some changes

Tested-by: Balbir Singh <bsingharora@...il.com>
Reviewed-by: Balbir Singh <bsingharora@...il.com>

Balbir