linux-kernel - Re: [PATCH] opp: fix a missing check on list iterator

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Message-ID: <20220328031739.72togwws2u2rlluo@vireshk-i7>
Date:   Mon, 28 Mar 2022 08:47:39 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>
Cc:     vireshk@...nel.org, nm@...com, sboyd@...nel.org,
        rafael.j.wysocki@...el.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] opp: fix a missing check on list iterator

On 27-03-22, 13:39, Xiaomeng Tong wrote:
> The bug is here:
>     dev = new_dev->dev;
> 
> The list iterator 'new_dev' will point to a bogus position containing
> HEAD if the list is empty or no element is found. This case must
> be checked before any use of the iterator, otherwise it will lead
> to a invalid memory access.
> 
> To fix this bug, add an check. Use a new variable 'iter' as the
> list iterator, while use the old variable 'new_dev' as a dedicated
> pointer to point to the found element.
> 
> Cc: stable@...r.kernel.org
> Fixes: deaa51465105a ("PM / OPP: Add debugfs support")
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
> ---
>  drivers/opp/debugfs.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/opp/debugfs.c b/drivers/opp/debugfs.c
> index 596c185b5dda..a4476985e4ce 100644
> --- a/drivers/opp/debugfs.c
> +++ b/drivers/opp/debugfs.c
> @@ -187,14 +187,19 @@ void opp_debug_register(struct opp_device *opp_dev, struct opp_table *opp_table)
>  static void opp_migrate_dentry(struct opp_device *opp_dev,
>  			       struct opp_table *opp_table)
>  {
> -	struct opp_device *new_dev;
> +	struct opp_device *new_dev = NULL, *iter;
>  	const struct device *dev;
>  	struct dentry *dentry;
>  
>  	/* Look for next opp-dev */
> -	list_for_each_entry(new_dev, &opp_table->dev_list, node)
> -		if (new_dev != opp_dev)
> +	list_for_each_entry(iter, &opp_table->dev_list, node)
> +		if (iter != opp_dev) {
> +			new_dev = iter;
>  			break;
> +		}
> +
> +	if (!new_dev)
> +		return;

I think you missed this check in the parent function ?

		if (!list_is_singular(&opp_table->dev_list)) {


i.e. this bug can never happen.

-- 
viresh