On Tue, May 12, 2015 at 08:59:03PM +0300, grygorii.stras...@linaro.org wrote:
> On 05/12/2015 07:42 PM, Dmitry Torokhov wrote:
> > On Tue, May 12, 2015 at 04:55:39PM +0300, grygorii.stras...@linaro.org
> > wrote:
> >> On 05/09/2015 12:05 AM, Dmitry Torokhov wrote:
> >>> On Fri, May 08, 2015 at 10:59:04PM +0200, Geert Uytterhoeven wrote:
> >>>> On Fri, May 8, 2015 at 7:19 PM, Dmitry Torokhov
> >>>> <dmitry.torok...@gmail.com> wrote:
> >>>>> On Fri, May 08, 2015 at 10:47:43AM +0200, Geert Uytterhoeven wrote:
> >>>>>> In the final iteration of commit 245bd6f6af8a62a2 ("PM / clock_ops: Add
> >>>>>> pm_clk_add_clk()"), a refcount increment was added by Grygorii
> >>>>>> Strashko.
> >>>>>> However, the accompanying IS_ERR() check operates on the wrong clock
> >>>>>> pointer, which is always zero at this point, i.e. not an error.
> >>>>>> This may lead to a NULL pointer dereference later, when __clk_get()
> >>>>>> tries to dereference an error pointer.
> >>>>>>
> >>>>>> Check the passed clock pointer instead to fix this.
> >>>>>
> >>>>> Frankly I would remove the check altogether. Why do we only check for
> >>>>> IS_ERR and not NULL or otherwise validate the pointer? The clk is passed
> >>>>
> >>>> __clk_get() does the NULL check.
> >>>
> >>> No, not really. It _handles_ clk being NULL and returns "everything is
> >>> fine". In any case it is __clk_get's decision what to do.
> >>>
> >>> I dislike gratuitous checks of arguments passed in. Instead of relying
> >>> on APIs refusing grabage we better not pass garbage to these APIs in the
> >>> first place. So I'd change it to trust that we are given a usable
> >>> pointer and simply do:
> >>>
> >>> if (!__clk_get(clk)) {
> >>> kfree(ce);
> >>> return -ENOENTl
> >>> }
> >>
> >> Not sure this is right thing to do, because this API initially
> >> was intended to be used as below [1]:
> >> clk = of_clk_get(dev->of_node, i));
> >> ret = pm_clk_add_clk(dev, clk);
> >> clk_put(clk);
> >>
> >> and of_clk_get may return ERR_PTR().
> >
> > Jeez, that sequence was not meant to be taken literally, it does miss
> > error handling completely. If you notice the majority of users of this
> > API do something like below:
> >
> > i = 0;
> > while ((clk = of_clk_get(dev->of_node, i++)) && !IS_ERR(clk)) {
> > dev_dbg(dev, "adding clock '%s' to list of PM clocks\n",
> > __clk_get_name(clk));
> > error = pm_clk_add_clk(dev, clk);
> > clk_put(clk);
> > if (error) {
> > dev_err(dev, "pm_clk_add_clk failed %d\n", error);
> > pm_clk_destroy(dev);
> > return error;
> > }
> > }
> >
> > i.e. it already validates clk pointer before passing it on since it
> > needs to know when to stop iterating.
>
> np. It's just my opinion - if you agree that code will just crash
> in case of passing invalid @clk argument (in worst case:)
>
> int __clk_get(struct clk *clk)
> {
> struct clk_core *core = !clk ? NULL : clk->core;
> ^^^ here
Yes, it will crash if you pass invalid pointer here, be it
ERR_PTR-encoded value, or, for example, 0x1, or maybe (void
*)random_32(). The latter will probably not crash right away, but cause
some random damage that will manifest later.
Thanks.
--
Dmitry
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