linux-kernel - Re: [PATCH] clk: fix a missing-free bug in clk_cpy

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Message-ID: <20190607120717.GA3109@zhanggen-UX430UQ>
Date:   Fri, 7 Jun 2019 20:07:17 +0800
From:   Gen Zhang <blackgod016574@...il.com>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     Stephen Boyd <sboyd@...nel.org>, mturquette@...libre.com,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: fix a missing-free bug in clk_cpy_name()

On Fri, Jun 07, 2019 at 11:10:37AM +0200, Jiri Slaby wrote:
> On 07. 06. 19, 3:52, Gen Zhang wrote:
> >>>>> @@ -3491,6 +3492,8 @@ static int clk_core_populate_parent_map(struct clk_core *core)
> >>>>>                             kfree_const(parents[i].name);
> >>>>>                             kfree_const(parents[i].fw_name);
> >>>>>                     } while (--i >= 0);
> >>>>> +                   kfree_const(parent->name);
> >>>>> +                   kfree_const(parent->fw_name);
> >>>>
> >>>> Both of them were just freed in the loop above, no?
> >>> for (i = 0, parent = parents; i < num_parents; i++, parent++)
> >>> Is 'parent' the same as the one from the loop above?
> >>
> >> Yes. Did it change somehow?
> > parent++?
> 
> parent++ is done after the loop body. Or what do you mean?
> 
> >>> Moreover, should 'parents[i].name' and 'parents[i].fw_name' be freed by
> >>> kfree_const()?
> >>>
> >>
> >> Yes? They're allocated with kstrdup_const() in clk_cpy_name(), or
> >> they're NULL by virtue of the kcalloc and then kfree_const() does
> >> nothing.
> > I re-examined clk_cpy_name(). They are the second parameter of 
> > clk_cpy_name(). The first parameter is allocated, not the second one.
> > So 'parent->name' and 'parent->fw_name' should be freed, not 
> > 'parents[i].name' or 'parents[i].fw_name'. Am I totally misunderstanding
> > this clk_cpy_name()? :-(
> 
> The second parameter (the source) is parent_data[i].*, not parents[i].*
> (the destination). parent->fw_name and parent->name are properly freed
> in the do {} while loop as parents[i].name and parents[i].fw_name, given
> i hasn't changed yet. I am not sure what you mean at all. Are you
> uncertain about the C code flow?
> 
> thanks,
> -- 
> js
> suse labs
Thanks your patient explainaton. I think I need some time to figure out
this part of code.

Thanks
Gen