[PATCH] x86: Fix possible null-pointer dereferences in untrack_pfn()

[Jia-Ju Bai]

In untrack_pfn(), there is an if statement on line 1058 to check whether
vma is NULL:
    if (vma && !(vma->vm_flags & VM_PAT))

When vma is NULL, vma is used on line 1064:
    if (follow_phys(vma, vma->vm_start, 0, &prot, &paddr))
and line 1069:
    size = vma->vm_end - vma->vm_start;

Thus, possible null-pointer dereferences may occur.

To fix these possible bugs, vma is checked on line 1063.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1...@gmail.com>
---
 arch/x86/mm/pat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index d9fbd4f69920..717456e7745e 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -1060,7 +1060,7 @@ void untrack_pfn(struct vm_area_struct *vma, unsigned 
long pfn,
 
        /* free the chunk starting from pfn or the whole chunk */
        paddr = (resource_size_t)pfn << PAGE_SHIFT;
-       if (!paddr && !size) {
+       if (vma && !paddr && !size) {
                if (follow_phys(vma, vma->vm_start, 0, &prot, &paddr)) {
                        WARN_ON_ONCE(1);
                        return;
-- 
2.17.0