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

[Richard W.M. Jones]

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?
>
> If so, is this something specific to NBD sockets, or would it actually
> make sense to have it as a generic option in UnixSocketAddress?

For other NBD sockets, most likely.  I'm not sure about Unix sockets
in general (as in: I know they also have the two label thing, but I
don't know if there's a situation where SVirt protects other sockets
apart from NBD sockets).  I'm sure Dan will know ...

By the way although it appears that setsockcreatecon_raw is setting a
global flag, it seems to actually use a thread-local variable, so
implementing this (although still ugly) would not require locks.

https://github.com/SELinuxProject/selinux/blob/32611aea6543e3a8f32635857e37b4332b0b5c99/libselinux/src/procattr.c#L347

Rich.

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