[PATCH 2/9] mm/z3fold: fix possible null pointer dereferencing

[Miaohe Lin <linmiaohe@huawei.com>]

alloc_slots could fail to allocate memory under heavy memory pressure. So
we should check zhdr->slots against NULL to avoid future null pointer
dereferencing.

Fixes: fc5488651c7d ("z3fold: simplify freeing slots")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/z3fold.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index c2260f5a5885..5d8c21f2bc59 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -940,9 +940,19 @@ static inline struct z3fold_header *__z3fold_alloc(struct z3fold_pool *pool,
 		}
 	}
 
-	if (zhdr && !zhdr->slots)
+	if (zhdr && !zhdr->slots) {
 		zhdr->slots = alloc_slots(pool, GFP_ATOMIC);
+		if (!zhdr->slots)
+			goto out_fail;
+	}
 	return zhdr;
+
+out_fail:
+	if (!kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
+		add_to_unbuddied(pool, zhdr);
+		z3fold_page_unlock(zhdr);
+	}
+	return NULL;
 }
 
 /*
-- 
2.23.0