linux-kernel - Re: [PATCH] ASoC: qcom: q6dsp: Fix an off-by-one in q6adm_alloc

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Date:   Thu, 21 Jul 2022 13:00:42 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Banajit Goswami <bgoswami@...cinc.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Banajit Goswami <bgoswami@...eaurora.org>,
        alsa-devel@...a-project.org,
        Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Subject: Re: [PATCH] ASoC: qcom: q6dsp: Fix an off-by-one in
 q6adm_alloc_copp()

On Thu, Jul 21, 2022 at 11:02:22AM +0200, Christophe JAILLET wrote:
> find_first_zero_bit() returns MAX_COPPS_PER_PORT at max here.
> So 'idx' should be tested with ">=" or the test can't match.
> 
> Fixes: 7b20b2be51e1 ("ASoC: qdsp6: q6adm: Add q6adm driver")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  sound/soc/qcom/qdsp6/q6adm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/soc/qcom/qdsp6/q6adm.c b/sound/soc/qcom/qdsp6/q6adm.c
> index 01f383888b62..1530e98df165 100644
> --- a/sound/soc/qcom/qdsp6/q6adm.c
> +++ b/sound/soc/qcom/qdsp6/q6adm.c
> @@ -217,7 +217,7 @@ static struct q6copp *q6adm_alloc_copp(struct q6adm *adm, int port_idx)
>  	idx = find_first_zero_bit(&adm->copp_bitmap[port_idx],
>  				  MAX_COPPS_PER_PORT);
>  
> -	if (idx > MAX_COPPS_PER_PORT)
> +	if (idx >= MAX_COPPS_PER_PORT)
>  		return ERR_PTR(-EBUSY);

Harshit asked me to write a Smatch check to prevent this bug in the
future.  I got his email before I got your patch.  :P  Attached.

sound/soc/qcom/qdsp6/q6adm.c:220 q6adm_alloc_copp() warn: impossible find_next_bit condition

I'll probably try to make this check more generic, but even the simple
find_first_zero_bit() version will probably find bugs in the future and
it was pretty simple to write.

regards,
dan carpenter



View attachment "check_find_next_bit_off_by_one.c" of type "text/x-csrc" (1750 bytes)