Messages in this thread | | | Date | Tue, 12 May 2015 09:42:54 -0700 | From | Dmitry Torokhov <> | Subject | Re: [PATCH] PM / clock_ops: Fix clock error check in __pm_clk_add() |
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On Tue, May 12, 2015 at 04:55:39PM +0300, Grygorii.Strashko@linaro.org wrote: > Hi Dmitry, > 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.torokhov@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.
Thanks.
-- Dmitry
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