Re: [PATCH v3] livepatch: Prevent to apply the patch once coming module notifier fails

Josh Poimboeuf
2015-05-18T15:22:30Z

On Mon, May 18, 2015 at 02:08:06PM +0200, Petr Mladek wrote:
> On Wed 2015-05-13 09:14:15, Josh Poimboeuf wrote:
> > On Tue, May 12, 2015 at 10:04:44PM +0800, Minfei Huang wrote:
> > > @@ -930,6 +932,7 @@ disabled:
> > > static int klp_module_notify(struct notifier_block *nb, unsigned long action,
> > > void *data)
> > > {
> > > + int ret;
> > > struct module *mod = data;
> > > struct klp_patch *patch;
> > > struct klp_object *obj;
> > > @@ -955,7 +958,13 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action,
> > >
> > > if (action == MODULE_STATE_COMING) {
> > > obj->mod = mod;
> > > - klp_module_notify_coming(patch, obj);
> > > + ret = klp_module_notify_coming(patch, obj);
> > > + if (ret) {
> > > + obj->mod = NULL;
> > > + pr_warn("patch '%s' is dead, remove it "
> > > + "or re-install the module '%s'\n",
> > > + patch->mod->name, obj->name);
> > > + }
> >
> > The patch isn't necessarily dead, since it might also include previously
> > enabled changes for vmlinux or other modules. It can actually be a
> > dangerous condition if there's a mismatch between old code in the module
> > and new code elsewhere. How about something like:
> >
> > "patch '%s' is in an inconsistent state!\n"
>
> It must not be dangerous, otherwise the patch could not get applied
> immediately.
>
> I would omit this message completely. It would just duplicate the
> warning printed by klp_module_notify_coming().

This error path doesn't mean that the entire patch isn't applied. It
only affects the subset of the patch which applies to the coming module.
So you can have a dangerous mismatch in the case of a patch which
patches multiple objects.

--
Josh