On 03/20/2018 09:21 AM, Eric Dumazet wrote: > > > On 03/20/2018 08:53 AM, Ursula Braun wrote: >> From: Hans Wippel <hwip...@linux.vnet.ibm.com> >> >> Currently, the SMC experimental TCP option in a SYN packet is lost on >> the server side when SYN Cookies are active. However, the corresponding >> SYNACK sent back to the client contains the SMC option. This causes an >> inconsistent view of the SMC capabilities on the client and server. >> >> This patch disables the SMC option in the SYNACK when SYN Cookies are >> active to avoid this issue. >> >> Signed-off-by: Hans Wippel <hwip...@linux.vnet.ibm.com> >> Signed-off-by: Ursula Braun <ubr...@linux.vnet.ibm.com> >> --- >> net/ipv4/tcp_output.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c >> index 383cac0ff0ec..22894514feae 100644 >> --- a/net/ipv4/tcp_output.c >> +++ b/net/ipv4/tcp_output.c >> @@ -3199,6 +3199,8 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, >> struct dst_entry *dst, >> /* Under synflood, we do not attach skb to a socket, >> * to avoid false sharing. >> */ >> + if (IS_ENABLED(CONFIG_SMC)) >> + ireq->smc_ok = 0; >> break; >> case TCP_SYNACK_FASTOPEN: >> /* sk is a const pointer, because we want to express multiple >> > > I disagree with net-next qualification. > > This fixes a bug, so please send it for net tree, and including an > appropriate Fixes: tag. >
Also, please do not add the fix in tcp_make_synack() tcp_make_synack() builds an skb, and really should not modify ireq, ideally. The only reason ireq is not const is because of the skb_set_owner_w(). I would clear it in cookie_v4_check()/cookie_v6_check() (We could have a common helper to allocate a TCP ireq btw, but this will wait a future patch for net-next)
