[PATCH 4.4 85/86] s390/mm: Check for valid vma before zapping in gmap_discard

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Janosch Frank <frankja@xxxxxxxxxxxxx>

commit 1843abd03250115af6cec0892683e70cf2297c25 upstream.

Userspace could have munmapped the area before doing unmapping from
the gmap. This would leave us with a valid vmaddr, but an invalid vma
from which we would try to zap memory.

Let's check before using the vma.

Fixes: 1e133ab296f3 ("s390/mm: split arch/s390/mm/pgtable.c")
Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Message-Id: <20180816082432.78828-1-frankja@xxxxxxxxxxxxx>
Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/s390/mm/pgtable.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -637,6 +637,8 @@ void gmap_discard(struct gmap *gmap, uns
 		vmaddr |= gaddr & ~PMD_MASK;
 		/* Find vma in the parent mm */
 		vma = find_vma(gmap->mm, vmaddr);
+		if (!vma)
+			continue;
 		size = min(to - gaddr, PMD_SIZE - (gaddr & ~PMD_MASK));
 		zap_page_range(vma, vmaddr, size, NULL);
 	}