linux-kernel - Re: [PATCH v2 1/1] bus: mhi: host: Fix up null pointer access in mhi_irq

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Date:   Thu, 21 Jul 2022 16:53:48 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Qiang Yu <quic_qianyu@...cinc.com>
Cc:     quic_hemantk@...cinc.com, loic.poulain@...aro.org,
        quic_jhugo@...cinc.com, mhi@...ts.linux.dev,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_cang@...cinc.com
Subject: Re: [PATCH v2 1/1] bus: mhi: host: Fix up null pointer access in
 mhi_irq_handler

On Thu, Jul 21, 2022 at 10:15:54AM +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@...cinc.com>
> ---
> v1->v2: change dev_err to dev_dbg
> 
>  drivers/bus/mhi/host/main.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
> index f3aef77a..25ea1f8 100644
> --- a/drivers/bus/mhi/host/main.c
> +++ b/drivers/bus/mhi/host/main.c
> @@ -430,12 +430,20 @@ 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;
>  

It'd be good to add a comment here on why we are checking for the NULL pointer.
Something like,

"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."

Thanks,
Mani

> +	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");
> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
> 

-- 
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