On 2022-12-23 03:42, Dan Carpenter wrote:
> On Tue, Dec 20, 2022 at 09:35:38AM -0700, Logan Gunthorpe wrote:
>>
>>
>> On 2022-12-19 23:17, Miaoqian Lin wrote:
>>> When all references are dropped, callback function plx_dma_release()
>>> for put_device() will call kfree(plxdev) to release memory.
>>> Fix the error path to fix the possible double free.
>>>
>>> Fixes: 07503e6aefe4 ("dmaengine: plx_dma: add a missing put_device() on error path")
>>> Signed-off-by: Miaoqian Lin <linmq006@xxxxxxxxx>
>>> ---
>>> Please correct me if I make mistakes, thanks for your review.
>>> ---
>>> drivers/dma/plx_dma.c | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/dma/plx_dma.c b/drivers/dma/plx_dma.c
>>> index 12725fa1655f..bce724ff4e16 100644
>>> --- a/drivers/dma/plx_dma.c
>>> +++ b/drivers/dma/plx_dma.c
>>> @@ -546,8 +546,9 @@ static int plx_dma_create(struct pci_dev *pdev)
>>> return 0;
>>>
>>> put_device:
>>> - put_device(&pdev->dev);
>>> free_irq(pci_irq_vector(pdev, 0), plxdev);
>>> + put_device(&pdev->dev);
>>> + return rc;
>>> free_plx:
>>> kfree(plxdev);
>>>
>>
>>
>> Sorry, after reviewing, I don't think this patch is correct.
>>
>> plx_dma_release() is called from dma_async_device_unregister() which
>> won't be called if dma_async_device_register() fails. It does not get
>> freed when the pci device is put. So I don't think this is a possible
>> double free.
>
> I think instead of "double free" it Miaoqian meant "use after free". It
> does look like a use after free to me. Certainly there is no harm from
> applying the patch and it makes the code more obviously correct.
Yeah, moving the put_device() up would certainly look more correct.
But I think it's actually not a bug either because plx_dma_create() is
called from the pci probe function, so the pci device cannot go away.
Logan
