linux-kernel - [PATCH] iommu: fix an incorrect NULL check on list iterator

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Message-Id: <20220327053558.2821-1-xiam0nd.tong@gmail.com>
Date:   Sun, 27 Mar 2022 13:35:58 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     agross@...nel.org
Cc:     bjorn.andersson@...aro.org, joro@...tes.org, will@...nel.org,
        sricharan@...eaurora.org, linux-arm-msm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Xiaomeng Tong <xiam0nd.tong@...il.com>, stable@...r.kernel.org
Subject: [PATCH] iommu: fix an incorrect NULL check on list iterator

The bug is here:
	if (!iommu || iommu->dev->of_node != spec->np) {

The list iterator value 'iommu' will *always* be set and non-NULL by
list_for_each_entry(), so it is incorrect to assume that the iterator
value will be NULL if the list is empty or no element is found (in fact,
it will point to a invalid structure object containing HEAD).

To fix the bug, run insert_iommu_master(dev, &iommu, spec); unlock and
return 0 when found, otherwise unlock and return -ENODEV.

Cc: stable@...r.kernel.org
Fixes: f78ebca8ff3d6 ("iommu/msm: Add support for generic master bindings")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
---
 drivers/iommu/msm_iommu.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/iommu/msm_iommu.c b/drivers/iommu/msm_iommu.c
index 3a38352b603f..1dbb8b0695ec 100644
--- a/drivers/iommu/msm_iommu.c
+++ b/drivers/iommu/msm_iommu.c
@@ -617,23 +617,17 @@ static int qcom_iommu_of_xlate(struct device *dev,
 {
 	struct msm_iommu_dev *iommu;
 	unsigned long flags;
-	int ret = 0;
 
 	spin_lock_irqsave(&msm_iommu_lock, flags);
 	list_for_each_entry(iommu, &qcom_iommu_devices, dev_node)
-		if (iommu->dev->of_node == spec->np)
-			break;
-
-	if (!iommu || iommu->dev->of_node != spec->np) {
-		ret = -ENODEV;
-		goto fail;
-	}
-
-	insert_iommu_master(dev, &iommu, spec);
-fail:
+		if (iommu->dev->of_node == spec->np) {
+			insert_iommu_master(dev, &iommu, spec);
+			spin_unlock_irqrestore(&msm_iommu_lock, flags);
+			return 0;
+		}
 	spin_unlock_irqrestore(&msm_iommu_lock, flags);
 
-	return ret;
+	return -ENODEV;
 }
 
 irqreturn_t msm_iommu_fault_handler(int irq, void *dev_id)
-- 
2.17.1