Re: [PATCH] drivers/char/ipmi_si: prevent null deref during module exit

[Corey Minyard]

On 11/08/2017 11:11 AM, Andrew Banman wrote:
> On 11/8/17 11:06 AM, Andrew Banman wrote:
> > If there are uninitialized SMIs in the smi_infos list, i.e. with no
> > handlers set, then disable_si_irq() in cleanup_smi_one() will hit a null
> > pointer dereference when the former attempts to start the check enables
> > transaction. Thus, we panic during module exit.
>
> I think this points to a broader problem of holding uninitialized 
> smi_info
> structs in smi_infos list. There are many places where handlers and 
> other struct
> members are assumed. Maybe a better design would be to remove SMIs 
> from the list
> if we have no intention of initializing them?

This begs the question: How did you produce this? From what I can tell,
there is no way you can get to this code if you don't have a working and
initialized smi_info structure, and that's not the only place this would
have to be fixed if it wasn't. So it's not what you assume, I don't think
it's an uninitialized smi_info structure on the list.

As usual with these sorts of things, please send tracebacks and reproduction
procedures.

If you are removing the module and this happens, there may be a race
conditions, but this is the wrong fix. More likely that the structure gets
cleaned up and this function is called afterwards.

-corey

> Andrew
>
> > Avoid panicking when there are uninitialized SMIs by checking for a 
> > handler
> > pointer before starting the check enables transaction.
> >
> > Signed-off-by: Andrew Banman <abanman@xxxxxxx>
> > ---
> > ÂÂdrivers/char/ipmi/ipmi_si_intf.c | 2 +-
> > ÂÂ1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/char/ipmi/ipmi_si_intf.c 
> > b/drivers/char/ipmi/ipmi_si_intf.c
> > index cb5719e..6c0b1b3 100644
> > --- a/drivers/char/ipmi/ipmi_si_intf.c
> > +++ b/drivers/char/ipmi/ipmi_si_intf.c
> > @@ -442,7 +442,7 @@ static void start_check_enables(struct smi_info 
> > *smi_info, bool start_timer)
> >
> > ÂÂÂÂÂ if (start_timer)
> > ÂÂÂÂÂÂÂÂÂ start_new_msg(smi_info, msg, 2);
> > -ÂÂÂ else
> > +ÂÂÂ else if (smi_info->handlers)
> > smi_info->handlers->start_transaction(smi_info->si_sm, msg, 2);
> > ÂÂÂÂÂ smi_info->si_state = SI_CHECKING_ENABLES;
> > ÂÂ}