Re: [PATCH v4] dma: at_hdmac: Fix use-after-free by proper tasklet cleanup

[Hongling Zeng <zhongling0719@126.com>]

在 2026年07月09日 05:32, Frank Li 写道:
> On Wed, Jul 08, 2026 at 10:59:59AM +0800, Hongling Zeng wrote:
>> Current cleanup paths have a use-after-free vulnerability:
>> - vchan_init() creates tasklets that access at_dma_chan memory
>> - free_irq() only waits for IRQ handler, NOT tasklets
>> - atdma is devm-managed and freed after probe/remove
>> - Running tasklets accessing freed memory → Use-After-Free!
>>
>> The fix requires careful ordering:
>> - free_irq() FIRST to synchronize with running IRQ handlers and prevent
>>    them from scheduling new tasklets
>> - Then kill tasklets to wait for already-scheduled ones to complete
>> - Only then free other resources
>>
>> Fixes: ac803b56860f ("dmaengine: at_hdmac: Convert driver to use virt-dma")
>> Reported-by: sashiko-bot@kernel.org
>> Closes: https://lore.kernel.org/all/20260604073945.54B311F00898@smtp.kernel.org/
>> Signed-off-by: Hongling Zeng <zenghongling@kylinos.cn>
>>
>> ---
>> Change in v4:
>>    - Fix error path fallthrough causing double-free_irq()
>>    - Use channel iteration index (chan_id not initialized before registration)
>>    - Remove unnecessary defensive checks
>> ---
>>   drivers/dma/at_hdmac.c | 31 ++++++++++++++++++++++---------
>>   1 file changed, 22 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
>> index e5b30a57c477..044a0fb38b7a 100644
>> --- a/drivers/dma/at_hdmac.c
>> +++ b/drivers/dma/at_hdmac.c
>> @@ -1940,6 +1940,20 @@ static void at_dma_off(struct at_dma *atdma)
>>   		cpu_relax();
>>   }
>>
>> +static void at_dma_cleanup_channels(struct at_dma *atdma)
>> +{
>> +	struct dma_chan *chan, *_chan;
>> +	int i = 0;
>> +
>> +	list_for_each_entry_safe(chan, _chan, &atdma->dma_device.channels,
>> +			device_node) {
>> +		/* Disable interrupts */
>> +		atc_disable_chan_irq(atdma, i++);
>> +		tasklet_kill(&to_at_dma_chan(chan)->vc.task);
>> +		list_del(&chan->device_node);
>> +	}
>> +}
>> +
>>   static int __init at_dma_probe(struct platform_device *pdev)
>>   {
>>   	struct at_dma		*atdma;
>> @@ -2105,12 +2119,17 @@ static int __init at_dma_probe(struct platform_device *pdev)
>>   err_of_dma_controller_register:
>>   	dma_async_device_unregister(&atdma->dma_device);
>>   err_dma_async_device_register:
>> +	free_irq(platform_get_irq(pdev, 0), atdma);
>> +	at_dma_cleanup_channels(atdma);
>>   	dma_pool_destroy(atdma->memset_pool);
>> +	dma_pool_destroy(atdma->lli_pool);
>> +	goto err_clk;
> I forget the reason why need goto here. Can you call disable_irq() or
> disable hardware irq and call synchronize_irq() at free_irq() place. then
> goto can fallback to below clean up code
>
> Frank
   Thank you for the suggestion. I've updated to v6 following your advice:
   - Replaced free_irq() with disable_irq() to allow fallthrough without 
goto
   - free_irq() is now called only once at err_desc_pool_create label
   The new approach ensures IRQ handler cannot schedule tasklets before 
tasklet_kill(), then free_irq() handles the actual release.

    Please help to review again.
Thanks!

>
>>   err_memset_pool_create:
>>   	dma_pool_destroy(atdma->lli_pool);
>>   err_desc_pool_create:
>>   	free_irq(platform_get_irq(pdev, 0), atdma);
>>   err_irq:
>> +err_clk:
>>   	clk_disable_unprepare(atdma->clk);
>>   	return err;
>>   }
>> @@ -2118,23 +2137,17 @@ static int __init at_dma_probe(struct platform_device *pdev)
>>   static void at_dma_remove(struct platform_device *pdev)
>>   {
>>   	struct at_dma		*atdma = platform_get_drvdata(pdev);
>> -	struct dma_chan		*chan, *_chan;
>>
>>   	at_dma_off(atdma);
>>   	if (pdev->dev.of_node)
>>   		of_dma_controller_free(pdev->dev.of_node);
>>   	dma_async_device_unregister(&atdma->dma_device);
>>
>> -	dma_pool_destroy(atdma->memset_pool);
>> -	dma_pool_destroy(atdma->lli_pool);
>>   	free_irq(platform_get_irq(pdev, 0), atdma);
>>
>> -	list_for_each_entry_safe(chan, _chan, &atdma->dma_device.channels,
>> -			device_node) {
>> -		/* Disable interrupts */
>> -		atc_disable_chan_irq(atdma, chan->chan_id);
>> -		list_del(&chan->device_node);
>> -	}
>> +	at_dma_cleanup_channels(atdma);
>> +	dma_pool_destroy(atdma->memset_pool);
>> +	dma_pool_destroy(atdma->lli_pool);
>>
>>   	clk_disable_unprepare(atdma->clk);
>>   }
>> --
>> 2.25.1
>>