[PATCH v2 RESEND] coresight: etm-perf: Fix reference count leak in etm_setup_aux

[Suzuki K Poulose]

On 19/12/2025 09:41, Leo Yan wrote:
> Hi,
> 
> On Fri, Dec 19, 2025 at 10:39:49AM +0800, Ma Ke wrote:
> 
> [...]
> 
>>  From the discussion, I note two possible fix directions:
>>
>> 1. Release the initial reference in etm_setup_aux() (current v2 patch)
>> 2. Modify the behavior of coresight_get_sink_by_id() itself so it
>> doesn't increase the reference count.
> 
> The option 2 is the right way to go.
> 
>> To ensure the correctness of the v3 patch, I'd like to confirm which
>> patch is preferred. If option 2 is the consensus, I'm happy to modify
>> the implementation of coresight_get_sink_by_id() as suggested.
> 
> It is good to use a separate patch to fix
> coresight_find_device_by_fwnode() mentioned by James:
> 
> diff --git a/drivers/hwtracing/coresight/coresight-platform.c b/drivers/hwtracing/coresight/coresight-platform.c
> index 0db64c5f4995..2b34f818ba88 100644
> --- a/drivers/hwtracing/coresight/coresight-platform.c
> +++ b/drivers/hwtracing/coresight/coresight-platform.c
> @@ -107,14 +107,16 @@ coresight_find_device_by_fwnode(struct fwnode_handle *fwnode)
>   	 * platform bus.
>   	 */
>   	dev = bus_find_device_by_fwnode(&platform_bus_type, fwnode);
> -	if (dev)
> -		return dev;
>   
>   	/*
>   	 * We have a configurable component - circle through the AMBA bus
>   	 * looking for the device that matches the endpoint node.
>   	 */
> -	return bus_find_device_by_fwnode(&amba_bustype, fwnode);
> +	if (!dev)
> +		dev = bus_find_device_by_fwnode(&amba_bustype, fwnode);
> +
> +	put_device(dev);

^^ NAK, see below.

> +	return dev;
>   }
>   
>   /*
> @@ -274,7 +276,6 @@ static int of_coresight_parse_endpoint(struct device *dev,
>   
>   	of_node_put(rparent);
>   	of_node_put(rep);
> -	put_device(rdev);

This doesn't look good. We can't use the "dev" reliably without the 
reference count. We are opening up use-after-free.

NAK for this.

Suzuki

>   
>   	return ret;
>   }
> 
> Thanks for working on this.