linux-kernel - Re: [PATCH] ASoC: da7219: Fix an out-of-bound read in an error handling path

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Date:   Wed, 23 Jun 2021 12:46:55 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     support.opensource@...semi.com, lgirdwood@...il.com,
        broonie@...nel.org, perex@...ex.cz, tiwai@...e.com,
        Adam.Thomson.Opensource@...semi.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] ASoC: da7219: Fix an out-of-bound read in an error
 handling path

On Wed, Jun 23, 2021 at 07:22:45AM +0200, Christophe JAILLET wrote:
> If 'of_clk_add_hw_provider()' fails, the previous 'for' loop will have
> run completely and 'i' is know to be 'DA7219_DAI_NUM_CLKS'.
> 
> In such a case, there will be an out-of-bounds access when using
> 'da7219->dai_clks_lookup[i]' and '&da7219->dai_clks_hw[i]'.
> 
> To avoid that, add a new label, 'err_free_all', which set the expected
> value of 'i' in such a case.
> 
> Fixes: 78013a1cf297 ("ASoC: da7219: Fix clock handling around codec level probe")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  sound/soc/codecs/da7219.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/soc/codecs/da7219.c b/sound/soc/codecs/da7219.c
> index 13009d08b09a..1e8b491d1fd3 100644
> --- a/sound/soc/codecs/da7219.c
> +++ b/sound/soc/codecs/da7219.c
> @@ -2204,12 +2204,14 @@ static int da7219_register_dai_clks(struct snd_soc_component *component)
>  					     da7219->clk_hw_data);
>  		if (ret) {
>  			dev_err(dev, "Failed to register clock provider\n");
> -			goto err;
> +			goto err_free_all;
>  		}
>  	}
>  
>  	return 0;
>  
> +err_free_all:
> +	i = DA7219_DAI_NUM_CLKS - 1;
>  err:
>  	do {
>  		if (da7219->dai_clks_lookup[i])

This do while statement is wrong and it leads to potentially calling
clk_hw_unregister() on clks that haven't been registered.

I think that calling clk_hw_unregister() on unregistered clocks is
supposed to okay but I found a case where it leads to a WARN_ON()
(Nothing else harmful).  It's in __clk_register() if the alloc_clk()
fails:

	hw->clk = alloc_clk(core, NULL, NULL);
        if (IS_ERR(hw->clk)) {
                ret = PTR_ERR(hw->clk);
                goto fail_create_clk;  // <- forgot to set hw->clk = NULL
        }

The better way to handle errors from loops is to clean up partial
iterations before doing the goto.  So add a clk_hw_unregister() if the
dai_clk_lookup = clkdev_hw_create() assignment fails.  Then use a
while (--i >= 0) loop in the unwind section:

err_free_all:
	i = DA7219_DAI_NUM_CLKS;
err:
	while (--i >= 0) {

regards,
dan carpenter