linux-kernel - [PATCH] mm/migrate: check for null vma before dereferencing it

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Message-Id: <20170411125102.19497-1-colin.king@canonical.com>
Date:   Tue, 11 Apr 2017 13:51:02 +0100
From:   Colin King <colin.king@...onical.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Minchan Kim <minchan@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-mm@...ck.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mm/migrate: check for null vma before dereferencing it

From: Colin Ian King <colin.king@...onical.com>

check if vma is null before dereferencing it, this avoiding any
potential null pointer dereferences on vma via the is_vm_hugetlb_page
call or the direct vma->vm_flags reference.

Detected with CoverityScan, CID#1427995 ("Dereference before null check")

Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 mm/migrate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 7958dfa01b16..039f7bc3b9ee 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2757,10 +2757,10 @@ int migrate_vma(const struct migrate_vma_ops *ops,
 	/* Sanity check the arguments */
 	start &= PAGE_MASK;
 	end &= PAGE_MASK;
-	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL))
-		return -EINVAL;
 	if (!vma || !ops || !src || !dst || start >= end)
 		return -EINVAL;
+	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL))
+		return -EINVAL;
 	if (start < vma->vm_start || start >= vma->vm_end)
 		return -EINVAL;
 	if (end <= vma->vm_start || end > vma->vm_end)
-- 
2.11.0