From: Yuchung Cheng <ycheng@google.com>
Date: Tue, 8 Jan 2019 18:12:24 -0800
Subject: bpf: correctly set initial window on active Fast Open sender
Patch-mainline: v5.0-rc3
Git-commit: 31aa6503a15ba00182ea6dbbf51afb63bf9e851d
References: bsc#1109837

The existing BPF TCP initial congestion window (TCP_BPF_IW) does not
to work on (active) Fast Open sender. This is because it changes the
(initial) window only if data_segs_out is zero -- but data_segs_out
is also incremented on SYN-data.  This patch fixes the issue by
proerly accounting for SYN-data additionally.

Fixes: fc7478103c84 ("bpf: Adds support for setting initial cwnd")
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/core/filter.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3843,7 +3843,7 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_so
 			/* Only some options are supported */
 			switch (optname) {
 			case TCP_BPF_IW:
-				if (val <= 0 || tp->data_segs_out > 0)
+				if (val <= 0 || tp->data_segs_out > tp->syn_data)
 					ret = -EINVAL;
 				else
 					tp->snd_cwnd = val;