On Fri, Jul 18, 2025 at 09:24:05 +0100, Daniel P. Berrangé wrote:
> On Fri, Jul 18, 2025 at 09:39:22AM +0200, Peter Krempa wrote:
> > On Thu, Jul 17, 2025 at 17:02:33 +0100, Daniel P. Berrangé wrote:
> > > On Thu, Jul 17, 2025 at 05:28:09PM +0200, Peter Krempa via Devel wrote:
> > > > From: Peter Krempa <pkre...@redhat.com>
> > > >
> > > > Similarly to how we iterate the list of CAs in the concatenated bundle
> > > > there's a possibility of the server/client certificates to be
> > > > concatenated as well.
> > > >
> > > > If for some case the first certificate is okay but the further one have
> > > > e.g. invalid signatures the validation code would not reject them but
> > > > we'd encounter failures later when gnutls tries to use them.
> > > >
> > > > Iterate also the client/server certs rather than just the CAs.
> > >
> > > Was there some bug that motivated this change ?
> >
> > Yes-ish. I've abused the fact that gnutls loads everything from the file
> > ...
> >
> >
> > >
> > > I'd like to keep libvirt's behaviour in sync with QEMU's
> > > behaviour to the greatest extent possible. I've just been
> > > finalizing changes to QEMU to cope with mutliple certs
> > > in the server-cert.pem file, but the semantics there are
> > > the certs are a chain of intermediate certs, all of which
> > > must be valid.
> > >
> > > ie, currently we allow
> > >
> > > ca-cert.pem server-cert.pem
> > > | |
> > > |------+--------------------------| |---+-------|
> > >
> > > Root CA -> Sub CA 1 -> Sub CA 2 -> Server Cert
> > >
> > > but the intent is to support
> > >
> > > ca-cert.pem server-cert.pem
> > > | |
> > > |------+--| |----------------------------+-------|
> > >
> > > Root CA -> Sub CA 1 -> Sub CA 2 -> Server Cert
> > >
> > >
> > > Or
> > >
> > > ca-cert.pem server-cert.pem
> > > | |
> > > |------+-------------| |---------------+-------|
> > >
> > > Root CA -> Sub CA 1 -> Sub CA 2 -> Server Cert
> >
> > ... meant to facilitate the above ....
> >
> >
> > >
> > > the rational is that these splits reflect how some CA will
> > > give you your certs to begin with, and we want to allow
> > > them to be used directly.
> > >
> > > My intent was to copy the QEMU change into libvirt once it
> > > was merged in QEMU, so from that POV I'm not a fan of making
> > > the some of the changes in this series.
> > >
> > > Beyond that I'm also working post-quantum crypto support,
> > > which will require us to load multiple distinct server-cert-NNN.pem
> > > files, each with an independant set of certs, which are selected
> > > at runtime based on negotiated ciphers in the TLS handshake.
> >
> > ... in order to load certs with different (also the fancy new
> > post-quantum) signature algorithms.
>
> To best of my knowledge that will not work. IIUC when you load
> a bundle of certs into a session with gnutls_credentials_set
> that is assumed to be a cert chain by GNUTLS.
Well with my test setup where I've:
- created 2 CAs (one with RSA one with MLDSA sig) and concatenated them
- created 4 server certs RSA+MLDSA sig both signed by each of the
above CAs
- created 4 client certs same as server certs.
I've then concatenated all 4 server certs into one file and sequentially
tested connecting with each of the 4 client certs.
And (when allowing mldsa sigs for both CA and normal signing [1]) it
worked (allowed connecting via TLS) for all of the 4 client certs.
IIRC I've checked in one scenario that actually MLDSA sigs were used but
didn't bother checking any further for any kind of security problems.
> To load multiple parallel certs, with different algorithms
> requires calling gnutls_credentials_set mutliple times,
> providing each distinct cert chain.
>
> Kind of annoying since it means every app using gnutls is
> guaranteed to need code changes to support PQC with
> parallel offerings of algorithms.
>
> > Since I didn't notice that the crypto policy in fedora 42 doesn't yet
> > trust some of those (e.g. mldsa65), some of the certificates I've
> > concatenated weren't actually passing the checks.
>
> Yep, even in rawhide the PQC stuff isn't fully ready for gnutls.
[1] Yes this is exactly what tripped me up originally, because MLDSA is
not allowed in the gnutls policy. When I've concatenated the certs
virt-pki-validate tripped up only if the mldsa signed certs were first.
If I put RSA certs first it passed but any of the combination using
MLDSA didn't work.
>
> The only place I'm aware of which has new enough gnutls is CentOS
> Stream, and even then you need custom crypto-policies to enable
> it fully.
>
>
> > Thus if you're going to be fixing both of these I'll just push the
> > cleanup patches.
>
> Yep, go ahead and push the cleanup ones
>
> With regards,
> Daniel
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