[PATCH 4.19 08/37] ip: fix tos reflection in ack and reset packets

Greg Kroah-Hartman
2020-09-25T12:53:59Z

From: Wei Wang <weiwan@google.com>

[ Upstream commit ba9e04a7ddf4f22a10e05bf9403db6b97743c7bf ]

Currently, in tcp_v4_reqsk_send_ack() and tcp_v4_send_reset(), we
echo the TOS value of the received packets in the response.
However, we do not want to echo the lower 2 ECN bits in accordance
with RFC 3168 6.1.5 robustness principles.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/ip_output.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -73,6 +73,7 @@
#include <net/icmp.h>
#include <net/checksum.h>
#include <net/inetpeer.h>
+#include <net/inet_ecn.h>
#include <net/lwtunnel.h>
#include <linux/bpf-cgroup.h>
#include <linux/igmp.h>
@@ -1582,7 +1583,7 @@ void ip_send_unicast_reply(struct sock *
if (IS_ERR(rt))
return;

- inet_sk(sk)->tos = arg->tos;
+ inet_sk(sk)->tos = arg->tos & ~INET_ECN_MASK;

sk->sk_priority = skb->priority;
sk->sk_protocol = ip_hdr(skb)->protocol;