[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 <redacted>
---
 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

On 06/12/2018 04:09 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 <redacted>

Signed-off-by: Eric Dumazet <edumazet@google.com>

Thanks !

On Wed, Jun 13, 2018 at 9:09 AM, Frank van der Linden
[off-list ref] wrote:

I've tested the IPv4 variant with some changes

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

Balbir

From: Frank van der Linden <redacted>
Date: Tue, 12 Jun 2018 23:09:37 +0000

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 <redacted>

Applied and queued up for -stable.

I know you mention the bug causing commit in your commit message,
but you should also still provide a proper Fixes: tag.  I took
care of it for you this time.

Thanks.

On 6/14/18 5:05 PM, David Miller wrote:

From: Frank van der Linden <redacted>
Date: Tue, 12 Jun 2018 23:09:37 +0000

quoted

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 <redacted>

Applied and queued up for -stable.

I know you mention the bug causing commit in your commit message,
but you should also still provide a proper Fixes: tag.  I took
care of it for you this time.

Thanks Dave, and thanks for reminding me of the Fixes: tag. Will add it
next time.

- Frank