Mercurial > dropbear
view sshpty.h @ 1788:1fc0012b9c38
Fix handling of replies to global requests (#112)
The current code assumes that all global requests want / need a reply.
This isn't always true and the request itself indicates if it wants a
reply or not.
It causes a specific problem with [email protected] messages.
These are sent by OpenSSH after authentication to inform the client of
potential other host keys for the host. This can be used to add a new
type of host key or to rotate host keys.
The initial information message from the server is sent as a global
request, but with want_reply set to false. This means that the server
doesn't expect an answer to this message. Instead the client needs to
send a prove request as a reply if it wants to receive proof of
ownership for the host keys.
The bug doesn't cause any current problems with due to how OpenSSH
treats receiving the failure message. It instead treats it as a
keepalive message and further ignores it.
Arguably this is a protocol violation though of Dropbear and it is only
accidental that it doesn't cause a problem with OpenSSH.
The bug was found when adding host keys support to libssh, which is more
strict protocol wise and treats the unexpected failure message an error,
also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145
for more information.
The fix here is to honor the want_reply flag in the global request and
to only send a reply if the other side expects a reply.
author | Dirkjan Bussink <d.bussink@gmail.com> |
---|---|
date | Thu, 10 Dec 2020 16:13:13 +0100 |
parents | fe6bca95afa7 |
children |
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/* $OpenBSD: sshpty.h,v 1.4 2002/03/04 17:27:39 stevesk Exp $ */ /* * Copied from openssh-3.5p1 source by Matt Johnston 2003 * * Author: Tatu Ylonen <[email protected]> * Copyright (c) 1995 Tatu Ylonen <[email protected]>, Espoo, Finland * All rights reserved * Functions for allocating a pseudo-terminal and making it the controlling * tty. * * As far as I am concerned, the code I have written for this software * can be used freely for any purpose. Any derived versions of this * software must be clearly marked as such, and if the derived work is * incompatible with the protocol description in the RFC file, it must be * called by a name other than "ssh" or "Secure Shell". */ #ifndef SSHPTY_H #define SSHPTY_H int pty_allocate(int *, int *, char *, int); void pty_release(const char *); void pty_make_controlling_tty(int *, const char *); void pty_change_window_size(int, int, int, int, int); void pty_setowner(struct passwd *, const char *); #endif /* SSHPTY_H */