Re: RE: [PATCH] pinctrl:sunplus: Add check for kmalloc

[Christophe JAILLET]

Le 25/05/2023 à 05:22, Wells Lu 呂芳騰 a écrit :
> > Le 23/05/2023 à 21:37, andy.shevchenko@xxxxxxxxx a écrit :
> > > Tue, May 23, 2023 at 05:39:51PM +0000, Wells Lu 呂芳騰 kirjoitti:
> > > > > > Fix Smatch static checker warning:
> > > > > > potential null dereference 'configs'. (kmalloc returns null)
> > >
> > > ...
> > >
> > > > > >    			configs = kmalloc(sizeof(*configs), GFP_KERNEL);
> > > > > > +			if (!configs)
> > > > >
> > > > > > +				return -ENOMEM;
> > > > >
> > > > > "Fixing" by adding a memory leak is not probably a good approach.
> > > >
> > > > Do you mean I need to free all memory which are allocated in this
> > > > subroutine before return -ENOMEM?
> > >
> > > This is my understanding of the code. But as I said... (see below)
> > >
> > > ...
> > >
> > > > > >    			configs = kmalloc(sizeof(*configs), GFP_KERNEL);
> > > > > > +			if (!configs)
> > > > > > +				return -ENOMEM;
> > > > >
> > > > > Ditto.
> > >
> > > ...
> > >
> > > > > It might be that I'm mistaken. In this case please add an
> > > > > explanation why in the commit message.
> > >
> > > ^^^
> >
> > Hmmm, not so sure.
> >
> > Should be looked at more carefully, but
> >     dt_to_map_one_config		(in /drivers/pinctrl/devicetree.c)
> >       .dt_node_to_map
> >         --> sppctl_dt_node_to_map
> >
> > Should dt_to_map_one_config() fail, pinctrl_dt_free_maps() is called (see
> > https://elixir.bootlin.com/linux/v6.4-rc1/source/drivers/pinctrl/devicetree.c#L281)
> >
> > pinctrl_dt_free_maps() calls dt_free_map(), which calls .dt_free_map, so
> > pinctrl_utils_free_map()
> > (see
> > https://elixir.bootlin.com/linux/v6.4-rc1/source/drivers/pinctrl/sunplus/sppctl.c#L97
> > 8)
> >
> > Finally the needed kfree seem to be called from here.
> > (see
> > https://elixir.bootlin.com/linux/v6.4-rc1/source/drivers/pinctrl/pinctrl-utils.c#L119
> > )
> >
> >
> > *This should obviously be double checked*, but looks safe to me.
> >
> >
> > BUT, in the same function, the of_get_parent() should be undone in case
> > of error, as done at the end of the function, in the normal path.
> > This one seems to be missing, should a memory allocation error occur.
> >
> >
> > Just my 2c,
> >
> > CJ
>
> Thank you for your comments.
>
>  From the report of kmemleak, returning -ENOMEM directly causes memory leak. We
> need to free any memory allocated in this subroutine before returning -ENOMEM.
>
> I'll send a new patch that will free the allocated memory and call of_node_put()
> when an error happens.

Hi,
(adding Dan in copy because the initial report is related to smatch)

I don't use kmemleak, but could you share some input about its report?


I've not rechecked my analysis, but it looked promising.
Maybe Dan could also give a look at it and confirm your finding, or dig 
further with smatch to make sure that its static analysis was complete 
enough.

CJ


> Best regards,
> Wells Lu