[Curdle] Spencer Dawkins' Yes on draft-ietf-curdle-ssh-ext-info-12: (with COMMENT)

[Spencer Dawkins <[e-mail]>]

Spencer Dawkins has entered the following ballot position for
draft-ietf-curdle-ssh-ext-info-12: Yes

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COMMENT:
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Thanks for a readable document. It was a pleasure to review.

I have a few comments, but "Spencer doesn't know much about SSH" might be a
fine response for most of them ;-)

In this text,

  Implementations MUST NOT send an incorrect indicator name for their
  role. Implementations MAY disconnect if the counter-party sends an
  incorrect indicator. If "ext-info-c" or "ext-info-s" ends up being
  negotiated as a key exchange method, the parties MUST disconnect.

why would a party that doen't support this extention disconnect?

I ask, because this looks like a MUST requirement that might apply to an
implementation that doesn't support this extension. If that's normal SSH
behavior, that's all I need to know :-)

In this text,

  If this extension takes effect, the renegotiated compression algorithm
  is activated for the very next SSH message after the trigger message:

  - Sent by the server, the trigger message is SSH_MSG_USERAUTH_SUCCESS.
  - Sent by the client, the trigger message is SSH_MSG_NEWCOMPRESS.

  If this extension takes effect, the client MUST send the following
  message shortly after receiving SSH_MSG_USERAUTH_SUCCESS:

    byte       SSH_MSG_NEWCOMPRESS (value 8)

  The purpose of NEWCOMPRESS is to avoid a race condition where the
  server cannot reliably know whether a message sent by the client was
  sent before or after receiving the server's USERAUTH_SUCCESS.

I THINK the point is that the client's SSH_MSG_NEWCOMPRESS is sent after
SSH_MSG_USERAUTH_SUCCESS, before the client sends its first SSH message that's
compressed using the newly negotiated compression algorithm, but "MUST send ...
shortly after receiving SSH_MSG_USERAUTH_SUCCESS" doesn't help me figure that
out - I'm mostly guessing, based on "the renegotiated compression algorithm is
activated for the very next SSH message after the trigger message". But (1) if
I got that wrong, it's at least unclear for TSV ADs, and (2) if I got that
right, I'm not understanding what "shortly after receiving" the trigger message
is saying - for example, I wondered if there's a timer involved, so that if a
client doesn't have messages to send, it should still send SSH_MSG_NEWCOMPRESS,
or the server will think something's wrong.

In this text,

  This extension MAY be sent by the client as follows:

    string      "elevation"
    string      choice of: "y" | "n" | "d"

  A client sends "y" to indicate its preference that the session should
  be elevated; "n" to not be elevated; and "d" for the server to use its
  default behavior. The server MAY disconnect if it receives a different
  extension value. If a client does not send the "elevation" extension,
  the server SHOULD act as if "d" was sent.

  The terms "elevation" and "elevated" refer to an operating system
  mechanism where an administrator user's logon session is associated
  with two security contexts: one limited, and one with administrative
  rights. To "elevate" such a session is to activate the security
  context with full administrative rights. For more information about
  this mechanism on Windows, see also [WINADMIN] and [WINTOKEN].

  If a client has included this extension, then after authentication, a
  server that supports this extension SHOULD indicate to the client
  whether elevation was done by sending the following global request:

    byte        SSH_MSG_GLOBAL_REQUEST
    string      "elevation"
    boolean     want reply = false
    boolean     elevation performed

I would find this easier to understand, if the paragraph defining the terms was
the first paragraph in the section, and then the description of the extension
(which uses the term "elevation") followed. It's not bad, the way it is, but
the reader has to read past the description to find out what the definition
means.

The security considerations are brief and refer to overarching security
considerations, which I understand because this is an extension, but

  Security considerations are discussed throughout this document. This
  document updates the SSH protocol as defined in [RFC4251] and related
  documents. The security considerations of [RFC4251] apply.

doesn't say anything about new security considerations to think about, when you
add support for elevation, which seems like it would be a new attack surface,
but I could imagine that adding elevation is the first step toward fewer SSH
server implementations that always run with administrative rights just in case
they ever need to use them, so the attack surface is getting smaller?

... And now I see that Mirja also asked about elevation, and your answer to her
was pretty much what I had guessed.  Maybe it's worth summarizing your answer
in section 3.4.