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From:   Qiang Yu <quic_qianyu@quicinc.com>
To:     <mani@kernel.org>, <quic_hemantk@quicinc.com>,
        <loic.poulain@linaro.org>, <quic_jhugo@quicinc.com>
CC:     <mhi@lists.linux.dev>, <linux-arm-msm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <quic_cang@quicinc.com>,
        Qiang Yu <quic_qianyu@quicinc.com>
Subject: [PATCH v3 1/1] bus: mhi: host: Fix up null pointer access in mhi_irq_handler
Date:   Fri, 22 Jul 2022 11:17:18 +0800
Message-ID: <1658459838-30802-1-git-send-email-quic_qianyu@quicinc.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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>
---
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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