Re: [PATCH] dmaengine: fix NULL pointer in channel unregistration function

[Dave Jiang <dave.jiang@intel.com>]

On 12/13/23 09:04, Amelie Delaunay wrote:
> __dma_async_device_channel_register() can fail. In case of failure,
> chan->local is freed (with free_percpu()), and chan->local is nullified.
> When dma_async_device_unregister() is called (because of managed API or
> intentionally by DMA controller driver), channels are unconditionally
> unregistered, leading to this NULL pointer:
> [    1.318693] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000d0
> [...]
> [    1.484499] Call trace:
> [    1.486930]  device_del+0x40/0x394
> [    1.490314]  device_unregister+0x20/0x7c
> [    1.494220]  __dma_async_device_channel_unregister+0x68/0xc0
> 
> Look at dma_async_device_register() function error path, channel device
> unregistration is done only if chan->local is not NULL.
> 
> Then add the same condition at the beginning of
> __dma_async_device_channel_unregister() function, to avoid NULL pointer
> issue whatever the API used to reach this function.
> 
> Fixes: d2fb0a043838 ("dmaengine: break out channel registration")
> Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> ---
>  drivers/dma/dmaengine.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index b7388ae62d7f..491b22240221 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -1103,6 +1103,9 @@ EXPORT_SYMBOL_GPL(dma_async_device_channel_register);
>  static void __dma_async_device_channel_unregister(struct dma_device *device,
>  						  struct dma_chan *chan)
>  {
> +	if (chan->local == NULL)
> +		return;
> +
>  	WARN_ONCE(!device->device_release && chan->client_count,
>  		  "%s called while %d clients hold a reference\n",
>  		  __func__, chan->client_count);