linux-kernel - Re: [PATCH v1 1/1] bus: mhi: host: Fix up null pointer access in mhi_irq

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Message-ID: <b56c0dfb-2858-c1f4-9cff-9e1d786e672a@quicinc.com>
Date:   Wed, 20 Jul 2022 08:15:30 -0600
From:   Jeffrey Hugo <quic_jhugo@...cinc.com>
To:     Qiang Yu <quic_qianyu@...cinc.com>, <mani@...nel.org>,
        <quic_hemantk@...cinc.com>, <loic.poulain@...aro.org>
CC:     <mhi@...ts.linux.dev>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_cang@...cinc.com>
Subject: Re: [PATCH v1 1/1] bus: mhi: host: Fix up null pointer access in
 mhi_irq_handler

On 7/20/2022 4:04 AM, 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>
> ---
>   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..7959457 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;
>   
> +	if (!mhi_cntrl->mhi_ctxt) {
> +		dev_err(&mhi_cntrl->mhi_dev->dev,
> +			"mhi_ctxt has been freed\n");

dev_dbg since you identified a scenario where this is expected?

> +		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");