[PATCH AUTOSEL 5.1 24/60] bpf, tcp: correctly handle DONT_WAIT flags and timeo == 0

[Sasha Levin]

From: John Fastabend <john.fastabend@xxxxxxxxx>

[ Upstream commit 5fa2ca7c4a3fc176f31b495e1a704862d8188b53 ]

The tcp_bpf_wait_data() routine needs to check timeo != 0 before
calling sk_wait_event() otherwise we may see unexpected stalls
on receiver.

Arika did all the leg work here I just formatted, posted and ran
a few tests.

Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
Reported-by: Arika Chen <eaglesora@xxxxxxxxx>
Suggested-by: Arika Chen <eaglesora@xxxxxxxxx>
Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/ipv4/tcp_bpf.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index 4a619c85daed..3d1e15401384 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -27,7 +27,10 @@ static int tcp_bpf_wait_data(struct sock *sk, struct sk_psock *psock,
 			     int flags, long timeo, int *err)
 {
 	DEFINE_WAIT_FUNC(wait, woken_wake_function);
-	int ret;
+	int ret = 0;
+
+	if (!timeo)
+		return ret;
 
 	add_wait_queue(sk_sleep(sk), &wait);
 	sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
-- 
2.20.1