linux-kernel - [PATCH] maple_tree: Fix potential NULL pointer dereference if mas_pop

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Message-ID: <20251018152305.1612722-1-hehuiwen@kylinos.cn>
Date: Sat, 18 Oct 2025 23:23:05 +0800
From: Huiwen He <hehuiwen@...inos.cn>
To: Liam.Howlett@...cle.com
Cc: aliceryhl@...gle.com,
	andrewjballance@...il.com,
	maple-tree@...ts.infradead.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Huiwen He <hehuiwen@...inos.cn>
Subject: [PATCH] maple_tree: Fix potential NULL pointer dereference if mas_pop_node() fails

mas_pop_node() may return NULL when memory allocation fails or when
mas->sheaf is invalid. Several callers of mas_pop_node() did not check
the return value and directly dereferenced the pointer, which could
lead to a NULL pointer dereference and kernel crash.

Fixes: 54a611b60590 ("maple_tree: add mas_pop_node() helper")
Signed-off-by: Huiwen He <hehuiwen@...inos.cn>
---
 lib/maple_tree.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 39bb779cb311..524e1cfb4439 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3085,6 +3085,9 @@ static inline void mas_root_expand(struct ma_state *mas, void *entry)
 	int slot = 0;
 
 	node = mas_pop_node(mas);
+	if (unlikely(!node))
+		return;
+
 	pivots = ma_pivots(node, type);
 	slots = ma_slots(node, type);
 	node->parent = ma_parent_ptr(mas_tree_parent(mas));
@@ -3367,6 +3370,9 @@ static inline void mas_new_root(struct ma_state *mas, void *entry)
 	}
 
 	node = mas_pop_node(mas);
+	if (unlikely(!node))
+		return;
+
 	pivots = ma_pivots(node, type);
 	slots = ma_slots(node, type);
 	node->parent = ma_parent_ptr(mas_tree_parent(mas));
@@ -3506,6 +3512,9 @@ static inline void mas_wr_node_store(struct ma_wr_state *wr_mas,
 		newnode = &reuse;
 	}
 
+	if (unlikely(!newnode))
+		return;
+
 	newnode->parent = mas_mn(mas)->parent;
 	dst_pivots = ma_pivots(newnode, wr_mas->type);
 	dst_slots = ma_slots(newnode, wr_mas->type);
-- 
2.43.0