Re: [PATCH v3 1/1] bus: mhi: host: Fix up null pointer access in mhi_irq_handler

[Manivannan Sadhasivam <mani@kernel.org>]

+ath11k, Kalle

On Fri, Jul 22, 2022 at 11:17:18AM +0800, Qiang Yu wrote:
> The irq handler for a shared IRQ ought to be prepared for running
> even now it's being freed. So let's check the pointer used by
> mhi_irq_handler to avoid null pointer access since it is probably
> released before freeing IRQ.
> 
> Signed-off-by: Qiang Yu <quic_qianyu@quicinc.com>

Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>

Thanks,
Mani

> ---
> v2->v3: add comments
> v1->v2: change dev_err to dev_dbg
> 
>  drivers/bus/mhi/host/main.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
> index f3aef77a..df0fbfe 100644
> --- a/drivers/bus/mhi/host/main.c
> +++ b/drivers/bus/mhi/host/main.c
> @@ -430,12 +430,25 @@ irqreturn_t mhi_irq_handler(int irq_number, void *dev)
>  {
>  	struct mhi_event *mhi_event = dev;
>  	struct mhi_controller *mhi_cntrl = mhi_event->mhi_cntrl;
> -	struct mhi_event_ctxt *er_ctxt =
> -		&mhi_cntrl->mhi_ctxt->er_ctxt[mhi_event->er_index];
> +	struct mhi_event_ctxt *er_ctxt;
>  	struct mhi_ring *ev_ring = &mhi_event->ring;
> -	dma_addr_t ptr = le64_to_cpu(er_ctxt->rp);
> +	dma_addr_t ptr;
>  	void *dev_rp;
>  
> +	/*
> +	 * If CONFIG_DEBUG_SHIRQ is set, the IRQ handler will get invoked during __free_irq()
> +	 * and by that time mhi_ctxt() would've freed. So check for the existence of mhi_ctxt
> +	 * before handling the IRQs.
> +	 */
> +	if (!mhi_cntrl->mhi_ctxt) {
> +		dev_dbg(&mhi_cntrl->mhi_dev->dev,
> +			"mhi_ctxt has been freed\n");
> +		return IRQ_HANDLED;
> +	}
> +
> +	er_ctxt = &mhi_cntrl->mhi_ctxt->er_ctxt[mhi_event->er_index];
> +	ptr = le64_to_cpu(er_ctxt->rp);
> +
>  	if (!is_valid_ring_ptr(ev_ring, ptr)) {
>  		dev_err(&mhi_cntrl->mhi_dev->dev,
>  			"Event ring rp points outside of the event ring\n");
> -- 
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>