linux-kernel - [PATCH v2] iommu: fix an incorrect NULL check on list iterator

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Date:   Sun,  1 May 2022 21:12:59 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     agross@...nel.org, bjorn.andersson@...aro.org, joro@...tes.org,
        will@...nel.org, sricharan@...eaurora.org
Cc:     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 v2] 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, use a new value 'iter' as the list iterator, while use
the old value 'iommu' as a dedicated variable to point to the found one,
and remove the unneeded check for 'iommu->dev->of_node != spec->np'
outside the loop.

Cc: stable@...r.kernel.org
Fixes: f78ebca8ff3d6 ("iommu/msm: Add support for generic master bindings")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
---
changes since v1:
 - add a new iter variable (suggested by Joerg Roedel)

v1: https://lore.kernel.org/all/20220327053558.2821-1-xiam0nd.tong@gmail.com/
---
 drivers/iommu/msm_iommu.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/msm_iommu.c b/drivers/iommu/msm_iommu.c
index 3a38352b603f..41a3231a6d13 100644
--- a/drivers/iommu/msm_iommu.c
+++ b/drivers/iommu/msm_iommu.c
@@ -615,16 +615,17 @@ static void insert_iommu_master(struct device *dev,
 static int qcom_iommu_of_xlate(struct device *dev,
 			       struct of_phandle_args *spec)
 {
-	struct msm_iommu_dev *iommu;
+	struct msm_iommu_dev *iommu = NULL, *iter;
 	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)
+	list_for_each_entry(iter, &qcom_iommu_devices, dev_node)
+		if (iter->dev->of_node == spec->np) {
+			iommu = iter;
 			break;
+		}
 
-	if (!iommu || iommu->dev->of_node != spec->np) {
+	if (!iommu) {
 		ret = -ENODEV;
 		goto fail;
 	}
-- 
2.17.1