ipv4: tcp: fix TOS value in ACK messages sent from TIME_WAIT

There is a long standing bug in linux tcp stack, about ACK messages sent
on behalf of TIME_WAIT sockets.

In the IP header of the ACK message, we choose to reflect TOS field of
incoming message, and this might break some setups.

Example of things that were broken :
  - Routing using TOS as a selector
  - Firewalls
  - Trafic classification / shaping

We now remember in timewait structure the inet tos field and use it in
ACK generation, and route lookup.

Notes :
 - We still reflect incoming TOS in RST messages.
 - We could extend MuraliRaja Muniraju patch to report TOS value in
netlink messages for TIME_WAIT sockets.
 - A patch is needed for IPv6

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 3c8dfa16614d..44d65d546e30 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -183,6 +183,7 @@ struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk, const int stat
                 tw->tw_daddr        = inet->inet_daddr;
                 tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
                 tw->tw_bound_dev_if = sk->sk_bound_dev_if;
+                tw->tw_tos          = inet->tos;
                 tw->tw_num          = inet->inet_num;
                 tw->tw_state        = TCP_TIME_WAIT;
                 tw->tw_substate     = state;