linux-kernel - [PATCH] drivers:of:property.c: fix a potential double put (release) bug

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Date:   Wed, 18 Aug 2021 21:09:50 +0800
From:   Wentao_Liang <Wentao_Liang_g@....com>
To:     robh+dt@...nel.org
Cc:     frowand.list@...il.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Wentao_Liang <Wentao_Liang_g@....com>
Subject: [PATCH] drivers:of:property.c: fix a potential double put (release) bug

In line 1423 (#1), of_link_to_phandle() is called. In the function
(line 1140, #2), "of_node_put(sup_np);" drops the reference to phandle
and may cause phandle to be released. However, after the function
returns, the phandle is subsequently dropped again (line 1424, #3) by
the same put function. Double putting the phandle can lead to an
incorrect reference count.

We believe that the first put of the phandle is unnecessary (#3). We
can fix the above bug by removing the redundant "of_node_put()" in line
1423.

1401 static int of_link_property(struct device_node *con_np,
				const char *prop_name)
1402 {
...
1409     while (!matched && s->parse_prop) {
...
1414
1415         while ((phandle = s->parse_prop(con_np, prop_name, i))) {
...
                 //#1 phandle is dropped in this function
1423             of_link_to_phandle(con_dev_np, phandle);

1424             //#3 the second drop to phandle
		 of_node_put(phandle);

1425             of_node_put(con_dev_np);
1426         }
...
1428     }
1429     return 0;
1430 }

1095 static int of_link_to_phandle(struct device_node *con_np,
1096                   struct device_node *sup_np)
1097 {
1098     struct device *sup_dev;
1099     struct device_node *tmp_np = sup_np;
...
1140     of_node_put(sup_np);  //#2 the first drop to phandle
			       //   (unnecessary)
1141
1142     return 0;
1143 }

Signed-off-by: Wentao_Liang <Wentao_Liang_g@....com>
---
 drivers/of/property.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/of/property.c b/drivers/of/property.c
index 6c028632f425..408fdde1a20c 100644
--- a/drivers/of/property.c
+++ b/drivers/of/property.c
@@ -1137,7 +1137,6 @@ static int of_link_to_phandle(struct device_node *con_np,
 	put_device(sup_dev);
 
 	fwnode_link_add(of_fwnode_handle(con_np), of_fwnode_handle(sup_np));
-	of_node_put(sup_np);
 
 	return 0;
 }
-- 
2.25.1