[PATCH 4.14 38/38] KVM: s390: prevent buffer overrun on memory hotplug during migration

[Greg Kroah-Hartman]

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

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

From: Christian Borntraeger <borntraeger@xxxxxxxxxx>

commit c2cf265d860882b51a200e4a7553c17827f2b730 upstream.

We must not go beyond the pre-allocated buffer. This can happen when
a new memory slot is added during migration.

Reported-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Fixes: 190df4a212a7 (KVM: s390: CMMA tracking, ESSA emulation, migration mode)
Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/s390/kvm/priv.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -1009,7 +1009,7 @@ static inline int do_essa(struct kvm_vcp
 		cbrlo[entries] = gfn << PAGE_SHIFT;
 	}
 
-	if (orc) {
+	if (orc && gfn < ms->bitmap_size) {
 		/* increment only if we are really flipping the bit to 1 */
 		if (!test_and_set_bit(gfn, ms->pgste_bitmap))
 			atomic64_inc(&ms->dirty_pages);