s390/mm: Check for valid vma before zapping in gmap_discard

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@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Message-Id: <20180816082432.78828-1-frankja@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index bb44990c8212..911c7ded35f1 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -708,11 +708,13 @@ void gmap_discard(struct gmap *gmap, unsigned long from, unsigned long to)
                 vmaddr |= gaddr & ~PMD_MASK;
                 /* Find vma in the parent mm */
                 vma = find_vma(gmap->mm, vmaddr);
+                if (!vma)
+                        continue;
                 /*
                  * We do not discard pages that are backed by
                  * hugetlbfs, so we don't have to refault them.
                  */
-                if (vma && is_vm_hugetlb_page(vma))
+                if (is_vm_hugetlb_page(vma))
                         continue;
                 size = min(to - gaddr, PMD_SIZE - (gaddr & ~PMD_MASK));
                 zap_page_range(vma, vmaddr, size);