linux-kernel - Re: [PATCH 1/2] clk: Fix __clk_get access to already freed owner field.

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Message-ID: <54D3C4E0.80608@codeaurora.org>
Date:	Thu, 05 Feb 2015 11:30:40 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Alban Browaeys <alban.browaeys@...il.com>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Mike Turquette <mturquette@...aro.org>
CC:	linux-kernel@...r.kernel.org, Alban Browaeys <prahal@...oo.com>
Subject: Re: [PATCH 1/2] clk: Fix __clk_get access to already freed owner
 field.

On 02/05/15 10:24, Alban Browaeys wrote:
> On the second call to __set_clk_parents from of_clk_set_defaults, here
> when registering the second fimc device the kernel OOPS in an "unhandled
> paging request at virtual address 6b6b6b77". This in __clk_get when
> dereferencing clk->owner.
>
> Move the clk free in the kref managed _clk_release call instead of
> plain __clk_put.
>
> Fixes: 035a61c314eb ("clk: Make clk API return per-user struct clk
> instances)
>
> Signed-off-by: Alban Browaeys <prahal@...oo.com>
> ---
>  drivers/clk/clk.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index df94668..8f33722 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -2485,15 +2485,18 @@ EXPORT_SYMBOL_GPL(clk_register);
>   */
>  static void __clk_release(struct kref *ref)
>  {
> -	struct clk_core *clk = container_of(ref, struct clk_core, ref);
> -	int i = clk->num_parents;
> +	struct clk_core *core = container_of(ref, struct clk_core, ref);
> +	struct clk *clk = container_of(&core, struct clk, core);

How does this work? struct clk_core doesn't have a struct clk inside it.

> +	int i = core->num_parents;
>  
> -	kfree(clk->parents);
> +	kfree(core->parents);
>  	while (--i >= 0)
> -		kfree_const(clk->parent_names[i]);
> +		kfree_const(core->parent_names[i]);

We don't have kfree_const() in the clk-next tree so please resend based
on clk-next, not linux-next.

> +
> +	kfree(core->parent_names);
> +	kfree_const(core->name);
> +	kfree(core);
>  
> -	kfree(clk->parent_names);
> -	kfree_const(clk->name);
>  	kfree(clk);
>  }
>  
> @@ -2671,8 +2674,6 @@ void __clk_put(struct clk *clk)
>  	clk_prepare_unlock();
>  
>  	module_put(owner);
> -
> -	kfree(clk);
>  }
>  
>  /***        clk rate change notifiers        ***/

I'm still confused. Care to send the actual backtrace and describe which
hardware you're running on (perhaps some dts file to look at)?

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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