[PATCH mm v2] mm: hugetlb: Add checks for NULL for vma returned from find_vma.

[Esina Ekaterina]

find_vma may return NULL, that's why its return value
 is usually checked for NULL. vma should be checked before dereferencing 

Found by Astra Linux on behalf of Linux Verification Center
(linuxtesting.org) with SVACE.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Esina Ekaterina <eesina@xxxxxxxxxxxxx>
---
 mm/hugetlb.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3499b3803384..2162bfcf8f46 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5394,9 +5394,6 @@ void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
 pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
 {
 	struct vm_area_struct *vma = find_vma(mm, addr);
-	struct address_space *mapping = vma->vm_file->f_mapping;
-	pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
-			vma->vm_pgoff;
 	struct vm_area_struct *svma;
 	unsigned long saddr;
 	pte_t *spte = NULL;
@@ -5406,18 +5403,25 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
 	if (!vma_shareable(vma, addr))
 		return (pte_t *)pmd_alloc(mm, pud, addr);
 
-	i_mmap_assert_locked(mapping);
-	vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) {
-		if (svma == vma)
-			continue;
+	if (vma && vma->vm_file && vm->vm_file->f_mapping
+		&& vma->vm_start && vma->vm->vm_pgoff) {
+		struct address_space *mapping = vma->vm_file->f_mapping;
+		pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
+			vma->vm_pgoff;
 
-		saddr = page_table_shareable(svma, vma, addr, idx);
-		if (saddr) {
-			spte = huge_pte_offset(svma->vm_mm, saddr,
-					       vma_mmu_pagesize(svma));
-			if (spte) {
-				get_page(virt_to_page(spte));
-				break;
+		i_mmap_assert_locked(mapping);
+		vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) {
+			if (svma == vma)
+				continue;
+
+			saddr = page_table_shareable(svma, vma, addr, idx);
+			if (saddr) {
+				spte = huge_pte_offset(svma->vm_mm, saddr,
+							vma_mmu_pagesize(svma));
+				if (spte) {
+					get_page(virt_to_page(spte));
+					break;
+				}
 			}
 		}
 	}
-- 
2.39.0