Re: [PATCH v2] tcp: verify the checksum of the first data segment in a new connection

[Eric Dumazet <eric.dumazet@gmail.com>]

On 06/12/2018 02:41 PM, Frank van der Linden 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@amazon.com>


This is way too complicated.

You should call tcp_checksum_complete() earlier and avoid all this mess.


IPV4 part shown here :

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index fed3f1c6616708997f621535efe9412e4afa0a50..7b5f32aa3835b0124b0a9bd342c371df7b46f471 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1730,6 +1730,10 @@ int tcp_v4_rcv(struct sk_buff *skb)
                        reqsk_put(req);
                        goto discard_it;
                }
+               if (unlikely(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;