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

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Message-ID: <8e0d461a-c633-0162-b9e6-c2166bc013fe@wanadoo.fr>
Date:   Wed, 23 Jun 2021 23:13:46 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     linux-kernel@...r.kernel.org
Cc:     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

Le 23/06/2021 à 11:46, Dan Carpenter a écrit :
> 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.

Obviously right.

Thanks for the review Dan.
I'll send a v2 in the coming days.

CJ
> 
> 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
> 
>