bpf: tcp_bpf_recvmsg should return EAGAIN when nonblocking and no data

We return 0 in the case of a nonblocking socket that has no data
available. However, this is incorrect and may confuse applications.
After this patch we do the correct thing and return the error
EAGAIN.

Quoting return codes from recvmsg manpage,

EAGAIN or EWOULDBLOCK
 The socket is marked nonblocking and the receive operation would
 block, or a receive timeout had been set and the timeout expired
 before data was received.

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index b7918d4caa300a15bec2858065b8f73d71cf6eb0..3b45fe530f91e2e1aa697888e11a78cf7e9d211e 100644 (file)
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -145,6 +145,7 @@ msg_bytes_ready:
                        ret = err;
                        goto out;
                }
+               copied = -EAGAIN;
        }
        ret = copied;
 out: