Re: [PATCH 1/2] clk: Don't dereference parent clock if is NULL

From: Javier Martinez Canillas
Date: Thu Feb 12 2015 - 08:36:07 EST

Hello Stephen,

Thanks a lot for your feedback.

On 02/11/2015 07:54 PM, Stephen Boyd wrote:
> On 02/11, Javier Martinez Canillas wrote:
>> --- a/drivers/clk/clk.c
>> +++ b/drivers/clk/clk.c
>> @@ -799,7 +799,7 @@ clk_mux_determine_rate_flags(struct clk_hw *hw, unsigned long rate,
>> /* if NO_REPARENT flag set, pass through to current parent */
>> if (core->flags & CLK_SET_RATE_NO_REPARENT) {
>> parent = core->parent;
>> - if (core->flags & CLK_SET_RATE_PARENT)
>> + if (core->flags & CLK_SET_RATE_PARENT && parent)
>> best = __clk_determine_rate(parent->hw, rate,
>> min_rate, max_rate);
>> else if (parent)
> Sorry this doesn't look right. Before all the recent changes to
> this file we would call __clk_round_rate() which would return 0
> if the first argument was NULL. Now we're going to take the else
> if path and do something different. So we need a parent ?
> parent->hw : NULL here.

Right, I'm not that familiar with the common clock framework so I
didn't realize I was changing the behavior, sorry about that...

> Of course, I wonder why a clock has the CLK_SET_RATE_PARENT flag
> set if it doesn't actually have a parent. That also seems wrong.

Yes, I did not face this issue and only patch #2 was enough to
fix my problem but the theoretical NULL pointer dereference
was found when reading the code.

I agree that a clock with that flag set should have at least one
parent but afaict there is no sanity check on clock registration.

And even if that was the case, I believe that the core should be
robust enough to check for NULL before trying to dereference it.

I'll post a v2 passing NULL as an argument and parent->hw if
parent is not NULL as you suggested.

Best regards,
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