[PATCH] iommu: fix KASAN use-after-free in iommu_insert_resv_region

[Eric Auger]

Store the new region type in a variable. In case the new region
gets merged into another one, the new node is freed and nr shall
not be used anymore.

Fixes: 4dbd258ff63e ("iommu: Revisit iommu_insert_resv_region()
implementation")
Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
Reported-by: Qian Cai <cai@xxxxxx>
CC: Stable <stable@xxxxxxxxxxxxxxx> #v5.3+
---
 drivers/iommu/iommu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index d658c7c6a2ab..338769f96d17 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -293,6 +293,8 @@ int iommu_insert_resv_region(struct iommu_resv_region *new,
 			     struct list_head *regions)
 {
 	struct iommu_resv_region *iter, *tmp, *nr, *top;
+	enum iommu_resv_type nr_type = new->type;
+
 	LIST_HEAD(stack);
 
 	nr = iommu_alloc_resv_region(new->start, new->length,
@@ -313,7 +315,7 @@ int iommu_insert_resv_region(struct iommu_resv_region *new,
 		phys_addr_t top_end, iter_end = iter->start + iter->length - 1;
 
 		/* no merge needed on elements of different types than @nr */
-		if (iter->type != nr->type) {
+		if (iter->type != nr_type) {
 			list_move_tail(&iter->list, &stack);
 			continue;
 		}
-- 
2.20.1