Re: [PATCH net] forcedeth: fix UAF of txrx_stats in nv_remove

From: Chenguang Zhao <redacted>

nv_remove() frees the per-CPU txrx_stats before unregister_netdev().
Until unregister completes, ndo_get_stats64, the NAPI/xmit data path,
and nv_close()/drain may still access txrx_stats, leading to a
use-after-free.

Free the stats only after unregister_netdev().

Fixes: f4b633b911fd ("forcedeth: use per cpu to collect xmit/recv statistics")
Signed-off-by: Chenguang Zhao <redacted>
---
  drivers/net/ethernet/nvidia/forcedeth.c | 6 ++++--
  1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/nvidia/forcedeth.c b/drivers/net/ethernet/nvidia/forcedeth.c
index 5b0435d7bc39..106885bd0f6b 100644
--- a/drivers/net/ethernet/nvidia/forcedeth.c
+++ b/drivers/net/ethernet/nvidia/forcedeth.c

@@ -6187,9 +6187,11 @@ static void nv_remove(struct pci_dev *pci_dev)
  	struct net_device *dev = pci_get_drvdata(pci_dev);
  	struct fe_priv *np = netdev_priv(dev);
  
-	free_percpu(np->txrx_stats);
-
+	/* txrx_stats is used by ndo_get_stats64 and the data path until
+	 * unregister_netdevice() has completed.
+	 */
  	unregister_netdev(dev);
+	free_percpu(np->txrx_stats);
  
  	nv_restore_mac_addr(pci_dev);