linux-kernel - [PATCH net] net/mlx4: prevent potential use after free in mlx4_en_do_uc

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Message-ID: <aNvMHX4g8RksFFvV@stanley.mountain>
Date: Tue, 30 Sep 2025 15:25:01 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Yan Burman <yanb@...lanox.com>
Cc: Tariq Toukan <tariqt@...dia.com>, Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Amir Vadai <amirv@...lanox.com>, netdev@...r.kernel.org,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH net] net/mlx4: prevent potential use after free in
 mlx4_en_do_uc_filter()

Print "entry->mac" before freeing "entry".  The "entry" pointer is
freed with kfree_rcu() so it's unlikely that we would trigger this
in real life, but it's safer to re-order it.

Fixes: cc5387f7346a ("net/mlx4_en: Add unicast MAC filtering")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
 drivers/net/ethernet/mellanox/mlx4/en_netdev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
index d2071aff7b8f..308b4458e0d4 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
@@ -1180,9 +1180,9 @@ static void mlx4_en_do_uc_filter(struct mlx4_en_priv *priv,
 				mlx4_unregister_mac(mdev->dev, priv->port, mac);
 
 				hlist_del_rcu(&entry->hlist);
-				kfree_rcu(entry, rcu);
 				en_dbg(DRV, priv, "Removed MAC %pM on port:%d\n",
 				       entry->mac, priv->port);
+				kfree_rcu(entry, rcu);
 				++removed;
 			}
 		}
-- 
2.51.0