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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Wed, 11 Dec 2013 17:29:21 +0100
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Subject: Re: [Qemu-devel] [PATCH] vnc: refuse to set a password with
	VNC_AUTH_NONE
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, Anthony Liguori <aliguori@amazon.com>

On Mi, 2013-12-11 at 17:06 +0100, Paolo Bonzini wrote:
> Il 11/12/2013 16:54, Gerd Hoffmann ha scritto:
> > Current code silently changes the authentication settings
> > in case you try to set a password without password authentication
> > turned on.  This is bad.  Return an error instead.
> > 
> > If we want allow changing auth settings at runtime this should
> > be done explicitly using a separate monitor command, not as
> > side effect of set_passwd.
> > 
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> 
> Isn't this backwards-incompatible?

Yes.  I think it is the correct thing nevertheless.

Users which want a passwort protected guests should configure vnc
correctly to avoid a unprotected window between qemu start and setting
the password.

Also note that enabling passwd auth via "set_passwd" side-effect
bypasses fips restrictions.

So this is a clear security improvement IMHO.

cheers,
  Gerd