linux-kernel - [PATCH 4.4 059/159] powerpc/iommu: Avoid derefence before pointer check

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Message-Id: <20191122100750.400464968@linuxfoundation.org>
Date:   Fri, 22 Nov 2019 11:27:30 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Breno Leitao <leitao@...ian.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.4 059/159] powerpc/iommu: Avoid derefence before pointer check

From: Breno Leitao <leitao@...ian.org>

[ Upstream commit 984ecdd68de0fa1f63ce205d6c19ef5a7bc67b40 ]

The tbl pointer is being derefenced by IOMMU_PAGE_SIZE prior the check
if it is not NULL.

Just moving the dereference code to after the check, where there will
be guarantee that 'tbl' will not be NULL.

Signed-off-by: Breno Leitao <leitao@...ian.org>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/kernel/iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index a8e3490b54e3b..4c9b5970af371 100644
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -764,9 +764,9 @@ dma_addr_t iommu_map_page(struct device *dev, struct iommu_table *tbl,
 
 	vaddr = page_address(page) + offset;
 	uaddr = (unsigned long)vaddr;
-	npages = iommu_num_pages(uaddr, size, IOMMU_PAGE_SIZE(tbl));
 
 	if (tbl) {
+		npages = iommu_num_pages(uaddr, size, IOMMU_PAGE_SIZE(tbl));
 		align = 0;
 		if (tbl->it_page_shift < PAGE_SHIFT && size >= PAGE_SIZE &&
 		    ((unsigned long)vaddr & ~PAGE_MASK) == 0)
-- 
2.20.1