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From: Sabrina Dubroca <sd@queasysnail.net>
To: netdev@vger.kernel.org
Cc: Sabrina Dubroca <sd@queasysnail.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	bpf@vger.kernel.org
Subject: [PATCH bpf] bpf: tcp: recv() should return 0 when the peer socket is closed
Date: Wed, 10 Jun 2020 12:19:43 +0200
Message-ID: <26038a28c21fea5d04d4bd4744c5686d3f2e5504.1591784177.git.sd@queasysnail.net> (raw)

If the peer is closed, we will never get more data, so
tcp_bpf_wait_data will get stuck forever. In case we passed
MSG_DONTWAIT to recv(), we get EAGAIN but we should actually get
0.

From man 2 recv:

    RETURN VALUE

    When a stream socket peer has performed an orderly shutdown, the
    return value will be 0 (the traditional "end-of-file" return).

This patch makes tcp_bpf_wait_data always return 1 when the peer
socket has been shutdown. Either we have data available, and it would
have returned 1 anyway, or there isn't, in which case we'll call
tcp_recvmsg which does the right thing in this situation.

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
---
 net/ipv4/tcp_bpf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index 2b915aafda42..7aa68f4aae6c 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -245,6 +245,9 @@ static int tcp_bpf_wait_data(struct sock *sk, struct sk_psock *psock,
 	DEFINE_WAIT_FUNC(wait, woken_wake_function);
 	int ret = 0;
 
+	if (sk->sk_shutdown & RCV_SHUTDOWN)
+		return 1;
+
 	if (!timeo)
 		return ret;
 
-- 
2.27.0


             reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-10 10:19 Sabrina Dubroca [this message]
2020-06-12 10:15 ` Jakub Sitnicki
2020-06-12 22:13   ` Alexei Starovoitov
2020-06-12 22:52     ` John Fastabend

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