Re: [PATCH v2 1/2] module: Add a new helper delete_module()

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Apr 24, 2024 at 08:09:05PM +0800, Yafang Shao wrote:
> On Sun, Apr 7, 2024 at 11:58 AM Yafang Shao <laoar.shao@gmail.com> wrote:
> >
> > Introduce a new helper function, delete_module(), designed to delete kernel
> > modules from locations outside of the `kernel/module` directory.
> >
> > No functional change.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  include/linux/module.h |  1 +
> >  kernel/module/main.c   | 82 ++++++++++++++++++++++++++++++++----------
> >  2 files changed, 65 insertions(+), 18 deletions(-)
> >
> > diff --git a/include/linux/module.h b/include/linux/module.h
> > index 1153b0d99a80..c24557f1b795 100644
> > --- a/include/linux/module.h
> > +++ b/include/linux/module.h
> > @@ -75,6 +75,7 @@ extern struct module_attribute module_uevent;
> >  /* These are either module local, or the kernel's dummy ones. */
> >  extern int init_module(void);
> >  extern void cleanup_module(void);
> > +extern int delete_module(struct module *mod);
> >
> >  #ifndef MODULE
> >  /**
> > diff --git a/kernel/module/main.c b/kernel/module/main.c
> > index e1e8a7a9d6c1..3b48ee66db41 100644
> > --- a/kernel/module/main.c
> > +++ b/kernel/module/main.c
> > @@ -695,12 +695,74 @@ EXPORT_SYMBOL(module_refcount);
> >  /* This exists whether we can unload or not */
> >  static void free_module(struct module *mod);
> >
> > +static void __delete_module(struct module *mod)
> > +{
> > +       char buf[MODULE_FLAGS_BUF_SIZE];
> > +
> > +       WARN_ON_ONCE(mod->state != MODULE_STATE_GOING);
> > +
> > +       /* Final destruction now no one is using it. */
> > +       if (mod->exit != NULL)
> > +               mod->exit();
> > +       blocking_notifier_call_chain(&module_notify_list,
> > +                                    MODULE_STATE_GOING, mod);
> > +       klp_module_going(mod);
> > +       ftrace_release_mod(mod);
> > +
> > +       async_synchronize_full();
> > +
> > +       /* Store the name and taints of the last unloaded module for diagnostic purposes */
> > +       strscpy(last_unloaded_module.name, mod->name, sizeof(last_unloaded_module.name));
> > +       strscpy(last_unloaded_module.taints, module_flags(mod, buf, false),
> > +               sizeof(last_unloaded_module.taints));
> > +
> > +       free_module(mod);
> > +       /* someone could wait for the module in add_unformed_module() */
> > +       wake_up_all(&module_wq);
> > +}
> > +
> > +int delete_module(struct module *mod)
> > +{
> > +       int ret;
> > +
> > +       mutex_lock(&module_mutex);
> > +       if (!list_empty(&mod->source_list)) {
> > +               /* Other modules depend on us: get rid of them first. */
> > +               ret = -EWOULDBLOCK;
> > +               goto out;
> > +       }
> > +
> > +       /* Doing init or already dying? */
> > +       if (mod->state != MODULE_STATE_LIVE) {
> > +               ret = -EBUSY;
> > +               goto out;
> > +       }
> > +
> > +       /* If it has an init func, it must have an exit func to unload */
> > +       if (mod->init && !mod->exit) {
> > +               ret = -EBUSY;
> > +               goto out;
> > +       }
> > +
> > +       if (try_release_module_ref(mod) != 0) {
> > +               ret = -EWOULDBLOCK;
> > +               goto out;
> > +       }
> > +       mod->state = MODULE_STATE_GOING;
> > +       mutex_unlock(&module_mutex);
> > +       __delete_module(mod);
> > +       return 0;
> > +
> > +out:
> > +       mutex_unlock(&module_mutex);
> > +       return ret;
> > +}
> > +
> >  SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
> >                 unsigned int, flags)
> >  {
> >         struct module *mod;
> >         char name[MODULE_NAME_LEN];
> > -       char buf[MODULE_FLAGS_BUF_SIZE];
> >         int ret, forced = 0;
> >
> >         if (!capable(CAP_SYS_MODULE) || modules_disabled)
> > @@ -750,23 +812,7 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
> >                 goto out;
> >
> >         mutex_unlock(&module_mutex);
> > -       /* Final destruction now no one is using it. */
> > -       if (mod->exit != NULL)
> > -               mod->exit();
> > -       blocking_notifier_call_chain(&module_notify_list,
> > -                                    MODULE_STATE_GOING, mod);
> > -       klp_module_going(mod);
> > -       ftrace_release_mod(mod);
> > -
> > -       async_synchronize_full();
> > -
> > -       /* Store the name and taints of the last unloaded module for diagnostic purposes */
> > -       strscpy(last_unloaded_module.name, mod->name, sizeof(last_unloaded_module.name));
> > -       strscpy(last_unloaded_module.taints, module_flags(mod, buf, false), sizeof(last_unloaded_module.taints));
> > -
> > -       free_module(mod);
> > -       /* someone could wait for the module in add_unformed_module() */
> > -       wake_up_all(&module_wq);
> > +       __delete_module(mod);
> >         return 0;
> >  out:
> >         mutex_unlock(&module_mutex);
> > --
> > 2.39.1
> >
> 
> Luis, Greg,
> 
> Since the last version, there hasn't been any response. Would you mind
> taking a moment to review it and provide your feedback on the
> kernel/module changes?

There was response on patch 2/2, which is why I deleted this from my
review queue a long time ago.

Please address that if you wish to, and then resend if you feel this is
still needed.

Personally, I really don't like this function you added...

thanks,

greg k-h