[PATCH v2 1/9] KVM: s390: Properly handle NULL pointer in dat_cond_set_storage_key()

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

Some callers pass NULL as oldkey. Calling page_cond_set_storage_key()
will cause that NULL pointer to get dereferenced.

Fix by checking for NULL and assigning the pointer to a dummy local
variable to avoid crashes.

Fixes: 8e03e8316eb2 ("KVM: s390: KVM page table management functions: storage keys")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
---
 arch/s390/kvm/dat.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kvm/dat.c b/arch/s390/kvm/dat.c
index 3f2d6e8902d7..165c704fcf29 100644
--- a/arch/s390/kvm/dat.c
+++ b/arch/s390/kvm/dat.c
@@ -722,9 +722,12 @@ int dat_cond_set_storage_key(struct kvm_s390_mmu_cache *mmc, union asce asce, gf
 	if (rc)
 		return rc;
 
-	if (!ptep)
+	if (!ptep) {
+		if (!oldkey)
+			oldkey = &prev;
 		return page_cond_set_storage_key(large_crste_to_phys(*crstep, gfn), skey, oldkey,
 						 nq, mr, mc);
+	}
 
 	old = pgste_get_lock(ptep);
 	pgste = old;
-- 
2.55.0