Re: [PATCH v2 2/2] fuse: Send security context of inode on file creation

[Vivek Goyal <vgoyal@redhat.com>]

On Tue, Nov 02, 2021 at 04:38:06PM +0100, Miklos Szeredi wrote:
> On Tue, 2 Nov 2021 at 16:30, Vivek Goyal <vgoyal@redhat.com> wrote:
> >
> > On Tue, Nov 02, 2021 at 03:00:30PM +0100, Miklos Szeredi wrote:
> > > On Tue, 12 Oct 2021 at 20:06, Vivek Goyal <vgoyal@redhat.com> wrote:
> 
> > > > @@ -633,7 +713,29 @@ static int create_new_entry(struct fuse_mount *fm, struct fuse_args *args,
> > > >         args->out_numargs = 1;
> > > >         args->out_args[0].size = sizeof(outarg);
> > > >         args->out_args[0].value = &outarg;
> > > > +
> > > > +       if (init_security) {
> > >
> >
> > Hi Miklos,
> >
> > > Instead of a new arg to create_new_entry(), this could check
> > > args.opcode != FUSE_LINK.
> >
> > Will do.
> >
> > >
> > > > +               unsigned short idx = args->in_numargs;
> > > > +
> > > > +               if ((size_t)idx >= ARRAY_SIZE(args->in_args)) {
> > > > +                       err = -ENOMEM;
> > > > +                       goto out_put_forget_req;
> > > > +               }
> > > > +
> > > > +               err = get_security_context(entry, mode, &security_ctx,
> > > > +                                          &security_ctxlen);
> > > > +               if (err)
> > > > +                       goto out_put_forget_req;
> > > > +
> > > > +               if (security_ctxlen > 0) {
> > >
> > > This doesn't seem right.  How would the server know if this is arg is missing?
> > >
> > > I think if FUSE_SECURITY_CTX was negotiated, then the secctx header
> > > will always need to be added to the MK* requests.
> >
> > Even for the case of FUSE_LINK request? I think I put this check because
> > FUSE_LINK is not sending secctx header. Other requests are appending
> > this header even if a security module is not loaded/enabled.
> 
> No, FUSE_LINK wouldn't even get this far.

You are right. My bad. So looks like this check will always be true
given the current code. get_security_context() will either all
headers with security context or just return zeroed "struct fuse_secctxs",
indicating there are no security context. 

If that's the case, I should be able to get rid of this check. I will
do some more testing.

> 
> > I guess it makes more sense to add secctx header even for FUSE_LINK
> > request. Just that header will mention 0 security contexts are
> > following. This will interface more uniform. I will make this change.
> 
> Why? FUSE_LINK is not an inode creation op, it just shares the
> instantiation part with creation.

Ok, got it. Makes sense. So no sending of zeroed security context header
with FUSE_LINK.

Vivek