Re: [PATCH v2] nbd/server: Add --selinux-label option

[Eric Blake <eblake@redhat.com>]

On Fri, Jul 23, 2021 at 05:38:06PM +0100, Daniel P. Berrangé wrote:
> On Fri, Jul 23, 2021 at 06:18:55PM +0200, Kevin Wolf wrote:
> > Am 23.07.2021 um 12:33 hat Richard W.M. Jones geschrieben:
> > > Under SELinux, Unix domain sockets have two labels.  One is on the
> > > disk and can be set with commands such as chcon(1).  There is a
> > > different label stored in memory (called the process label).  This can
> > > only be set by the process creating the socket.  When using SELinux +
> > > SVirt and wanting qemu to be able to connect to a qemu-nbd instance,
> > > you must set both labels correctly first.
> > > 
> > > For qemu-nbd the options to set the second label are awkward.  You can
> > > create the socket in a wrapper program and then exec into qemu-nbd.
> > > Or you could try something with LD_PRELOAD.
> > > 
> > > This commit adds the ability to set the label straightforwardly on the
> > > command line, via the new --selinux-label flag.  (The name of the flag
> > > is the same as the equivalent nbdkit option.)
> > > 
> > > A worked example showing how to use the new option can be found in
> > > this bug: https://bugzilla.redhat.com/show_bug.cgi?id=1984938
> > > 
> > > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1984938
> > > Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> > 
> > I suppose this would also be relevant for the built-in NBD server,
> > especially in the context of qemu-storage-daemon?
> 
> It depends on the usage scenario really. nbdkit / qemu-nbd are
> not commonly run under any SELinux policy, so then end up being
> unconfined_t. A QEMU NBD client can't connect to an unconfined_t
> socket, so we need to override it with this arg.
> 
> In the case of qemu system emulator, under libvirt, it will
> already have a svirt_t type, so in that case there is no need
> to override the type for the socket.
> 
> For qsd there's not really any strong practice established
> but i expect most current usage is unconfined_t too and
> would benefit from setting label.
> 
> > If so, is this something specific to NBD sockets, or would it actually
> > make sense to have it as a generic option in UnixSocketAddress?
> 
> It is applicable to inet sockets too in fact.

So now that 6.2 is open, should I queue the patch as is, or wait for a
v3 that makes the option more generic to all socket usage?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org