RE: [PATCH] Remove redundant cleanup in ipmi_register_smi

["Ernst, Justin" <justin.ernst@hpe.com>]

> -----Original Message-----
> From: Corey Minyard [mailto:tcminyard@gmail.com]
> Sent: Wednesday, August 22, 2018 11:28 AM
> To: Ernst, Justin <justin.ernst@hpe.com>; Corey Minyard
> <minyard@acm.org>
> Cc: Arnd Bergmann <arnd@arndb.de>; Greg Kroah-Hartman
> <gregkh@linuxfoundation.org>; Jeremy Kerr <jk@ozlabs.org>; openipmi-
> developer@lists.sourceforge.net; linux-kernel@vger.kernel.org; Anderson,
> Russ <russ.anderson@hpe.com>
> Subject: Re: [PATCH] Remove redundant cleanup in ipmi_register_smi
> 
> On 08/21/2018 10:25 AM, Justin Ernst wrote:
> > When ipmi_register_smi fails, it performs a small cleanup routine
> > before returning its error value. In try_smi_init, on the condition
> > that ipmi_register_smi fails, ipmi_unregister_smi is called.
> > ipmi_unregister_smi performs the same cleanup routine as
> > ipmi_register_smi. This results in a kernel NULL pointer dereference.
> > Removing the cleanup routine in ipmi_register_smi results in proper
> cleanup of a ipmi_register_smi failure.
> 
> This is almost certainly wrong.  If ipmi_register_smi() fails, the calling code
> shouldn't call ipmi_unregister_smi().
> 
> However, I think I know what is going wrong.  ipmi_register_smi() can fail
> after the interface is initialized, if so the registering code will think it is
> registered and call ipmi_unregister_smi() on a failure.  I'll send a patch for
> this.
> 
> -corey

Thanks for the reply Corey. I agree with what you have stated. I'll be watching for the patch.
-Justin

> 
> >
> > Cc: Corey Minyard <minyard@acm.org>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Jeremy Kerr <jk@ozlabs.org>
> > Cc: openipmi-developer@lists.sourceforge.net
> > Cc: linux-kernel@vger.kernel.org
> > Cc: Russ Anderson <russ.anderson@hpe.com>
> > Acked-by: Andrew Banman <abanman@hpe.com>
> > Signed-off-by: Justin Ernst <justin.ernst@hpe.com>
> > ---
> >   drivers/char/ipmi/ipmi_msghandler.c | 10 +++++-----
> >   1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/char/ipmi/ipmi_msghandler.c
> > b/drivers/char/ipmi/ipmi_msghandler.c
> > index 51832b8a2c62..3b0b50c4f064 100644
> > --- a/drivers/char/ipmi/ipmi_msghandler.c
> > +++ b/drivers/char/ipmi/ipmi_msghandler.c
> > @@ -3395,12 +3395,12 @@ int ipmi_register_smi(const struct
> > ipmi_smi_handlers *handlers,
> >
> >    out:
> >   	if (rv) {
> > -		ipmi_bmc_unregister(intf);
> > -		list_del_rcu(&intf->link);
> > +		/*
> > +		 * ipmi_unregister_smi must be called to clean up after
> > +		 * failure. We unlock the mutex to allow ipmi_unregister_smi
> > +		 * to lock it and perform cleanup.
> > +		 */
> >   		mutex_unlock(&ipmi_interfaces_mutex);
> > -		synchronize_srcu(&ipmi_interfaces_srcu);
> > -		cleanup_srcu_struct(&intf->users_srcu);
> > -		kref_put(&intf->refcount, intf_free);
> >   	} else {
> >   		/*
> >   		 * Keep memory order straight for RCU readers.  Make
>