[Bug 264600] openssh: sshd spamming logs: error: Fssh_kex_exchange_identification: Connection closed by remote host

From: <bugzilla-noreply_at_freebsd.org>
Date: Wed, 05 Oct 2022 20:41:40 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=264600

--- Comment #15 from Ed Maste <emaste@freebsd.org> ---
(In reply to Jose Luis Duran from comment #0)
> After upgrading a public-facing SSH server to OpenSSH 8.8

What version were you running before?

This error comes from:
                        len = atomicio(read, ssh_packet_get_connection_in(ssh),
                            &c, 1);
                        if (len != 1 && errno == EPIPE) {
                                error_f("Connection closed by remote host");
                                r = SSH_ERR_CONN_CLOSED;
                                goto out;

This commit in OpenSSH-portable is probably relevant:

commit 0a843d9a0e805f14653a555f5c7a8ba99d62c12d
Author: djm@openbsd.org <djm@openbsd.org>
Date:   Thu Dec 27 03:25:24 2018 +0000

    upstream: move client/server SSH-* banners to buffers under

    ssh->kex and factor out the banner exchange. This eliminates some common
code
    from the client and server.

    Also be more strict about handling \r characters - these should only
    be accepted immediately before \n (pointed out by Jann Horn).

    Inspired by a patch from Markus Schmidt.
    (lots of) feedback and ok markus@

    OpenBSD-Commit-ID: 1cc7885487a6754f63641d7d3279b0941890275b

which came between 7.9 and 8.0

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