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Date:   Wed, 17 Jun 2020 21:03:28 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Sabrina Dubroca <sd@...asysnail.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: [PATCH AUTOSEL 5.7 111/388] bpf: tcp: Recv() should return 0 when the peer socket is closed

From: Sabrina Dubroca <sd@...asysnail.net>

[ Upstream commit 2c7269b231194aae23fb90ab65842573a91acbc9 ]

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@...asysnail.net>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Acked-by: Jakub Sitnicki <jakub@...udflare.com>
Link: https://lore.kernel.org/bpf/26038a28c21fea5d04d4bd4744c5686d3f2e5504.1591784177.git.sd@queasysnail.net
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 629aaa9a1eb9..9c5540887fbe 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -242,6 +242,9 @@ 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;
 
-- 
2.25.1

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