[PATCH 5.10 086/116] net: dsa: mv88e6xxx: fix use-after-free in mv88e6xxx_mdios_unregister

[Greg Kroah-Hartman]

From: Vladimir Oltean <vladimir.oltean@xxxxxxx>

[ Upstream commit 51a04ebf21122d5c76a716ecd9bfc33ea44b2b39 ]

Since struct mv88e6xxx_mdio_bus *mdio_bus is the bus->priv of something
allocated with mdiobus_alloc_size(), this means that mdiobus_free(bus)
will free the memory backing the mdio_bus as well. Therefore, the
mdio_bus->list element is freed memory, but we continue to iterate
through the list of MDIO buses using that list element.

To fix this, use the proper list iterator that handles element deletion
by keeping a copy of the list element next pointer.

Fixes: f53a2ce893b2 ("net: dsa: mv88e6xxx: don't use devres for mdiobus")
Reported-by: Rafael Richter <rafael.richter@xxxxxx>
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Link: https://lore.kernel.org/r/20220210174017.3271099-1-vladimir.oltean@xxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 9b451b820d7a6..1992be77522ac 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -3122,10 +3122,10 @@ static int mv88e6xxx_mdio_register(struct mv88e6xxx_chip *chip,
 static void mv88e6xxx_mdios_unregister(struct mv88e6xxx_chip *chip)
 
 {
-	struct mv88e6xxx_mdio_bus *mdio_bus;
+	struct mv88e6xxx_mdio_bus *mdio_bus, *p;
 	struct mii_bus *bus;
 
-	list_for_each_entry(mdio_bus, &chip->mdios, list) {
+	list_for_each_entry_safe(mdio_bus, p, &chip->mdios, list) {
 		bus = mdio_bus->bus;
 
 		if (!mdio_bus->external)
-- 
2.34.1