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

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Date:   Tue, 12 Jun 2018 23:09:37 +0000
From:   Frank van der Linden <fllinden@...zon.com>
To:     <edumazet@...gle.com>, <netdev@...r.kernel.org>
CC:     <fllinden@...zon.com>
Subject: [PATCH v3] tcp: verify the checksum of the first data segment in
 a new connection

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;
-- 
1.8.3.1