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    Subject[PATCH 5.7 110/477] bpf: tcp: Recv() should return 0 when the peer socket is closed
    Date
    From: Sabrina Dubroca <sd@queasysnail.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@queasysnail.net>
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>
    Acked-by: Jakub Sitnicki <jakub@cloudflare.com>
    Link: https://lore.kernel.org/bpf/26038a28c21fea5d04d4bd4744c5686d3f2e5504.1591784177.git.sd@queasysnail.net
    Signed-off-by: Sasha Levin <sashal@kernel.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 629aaa9a1eb99..9c5540887fbe5 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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