[PATCH 4.20 062/183] bpf: correctly set initial window on active Fast Open sender

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 31aa6503a15ba00182ea6dbbf51afb63bf9e851d ]

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@xxxxxxxxxx>
Reviewed-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Acked-by: Lawrence Brakmo <brakmo@xxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/core/filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index eb0007f30142b..fa9452406f214 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4019,7 +4019,7 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 			/* 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;
-- 
2.19.1