Re: [PATCH 3/5] tools/libs/store: drop read-only functionality

[Jürgen Groß <jgross@xxxxxxxx>]

On 07.10.20 12:54, Wei Liu wrote:
> On Fri, Oct 02, 2020 at 05:41:39PM +0200, Juergen Gross wrote:
> > Today it is possible to open the connection in read-only mode via
> > xs_daemon_open_readonly(). This is working only with Xenstore running
> > as a daemon in the same domain as the user. Additionally it doesn't
> > add any security as accessing the socket used for that functionality
> > requires the same privileges as the socket used for full Xenstore
> > access.
> >
> > So just drop the read-only semantics in all cases, leaving the
> > interface existing only for compatibility reasons. This in turn
> > requires to just ignore the XS_OPEN_READONLY flag.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> >   tools/libs/store/include/xenstore.h | 8 --------
> >   tools/libs/store/xs.c               | 7 ++-----
> >   2 files changed, 2 insertions(+), 13 deletions(-)
> >
> > diff --git a/tools/libs/store/include/xenstore.h 
> > b/tools/libs/store/include/xenstore.h
> > index cbc7206a0f..158e69ef83 100644
> > --- a/tools/libs/store/include/xenstore.h
> > +++ b/tools/libs/store/include/xenstore.h
> > @@ -60,15 +60,12 @@ typedef uint32_t xs_transaction_t;
> >   /* Open a connection to the xs daemon.
> >    * Attempts to make a connection over the socket interface,
> >    * and if it fails, then over the  xenbus interface.
> > - * Mode 0 specifies read-write access, XS_OPEN_READONLY for
> > - * read-only access.
> >    *
> >    * * Connections made with xs_open(0) (which might be shared page or
> >    *   socket based) are only guaranteed to work in the parent after
> >    *   fork.
> >    * * xs_daemon_open*() and xs_domain_open() are deprecated synonyms
> >    *   for xs_open(0).
> > - * * XS_OPEN_READONLY has no bearing on any of this.
> >    *
> >    * Returns a handle or NULL.
> >    */
> > @@ -83,11 +80,6 @@ void xs_close(struct xs_handle *xsh /* NULL ok */);
> >    */
> >   struct xs_handle *xs_daemon_open(void);
> >   struct xs_handle *xs_domain_open(void);
> > -
> > -/* Connect to the xs daemon (readonly for non-root clients).
> > - * Returns a handle or NULL.
> > - * Deprecated, please use xs_open(XS_OPEN_READONLY) instead
> > - */
> >   struct xs_handle *xs_daemon_open_readonly(void);
> >   
> >   /* Close the connection to the xs daemon.
> > diff --git a/tools/libs/store/xs.c b/tools/libs/store/xs.c
> > index 320734416f..4ac73ec317 100644
> > --- a/tools/libs/store/xs.c
> > +++ b/tools/libs/store/xs.c
> > @@ -302,7 +302,7 @@ struct xs_handle *xs_daemon_open(void)
> >   
> >   struct xs_handle *xs_daemon_open_readonly(void)
> >   {
> > -       return xs_open(XS_OPEN_READONLY);
> > +       return xs_open(0);
> >   }
> This changes the semantics of this function, isn't it? In that the user
> expects a readonly connection but in fact a read-write connection is
> returned.
>
> Maybe we should return an error here?
No, as the behavior is this way already if any of the following is true:

- a guest is opening the connection
- Xenstore is running in a stubdom
- oxenstored is being used


Juergen