[PATCH net v2] net: fix NULL pointer dereference in l3mdev_l3_rcv

[Wang Liang]

When delete l3s ipvlan:

    ip link del link eth0 ipvlan1 type ipvlan mode l3s

This may cause a null pointer dereference:

    Call trace:
     ip_rcv_finish+0x48/0xd0
     ip_rcv+0x5c/0x100
     __netif_receive_skb_one_core+0x64/0xb0
     __netif_receive_skb+0x20/0x80
     process_backlog+0xb4/0x204
     napi_poll+0xe8/0x294
     net_rx_action+0xd8/0x22c
     __do_softirq+0x12c/0x354

This is because l3mdev_l3_rcv() visit dev->l3mdev_ops after
ipvlan_l3s_unregister() assign the dev->l3mdev_ops to NULL. The process
like this:

    (CPU1)                     | (CPU2)
    l3mdev_l3_rcv()            |
      check dev->priv_flags:   |
        master = skb->dev;     |
                               |
                               | ipvlan_l3s_unregister()
                               |   set dev->priv_flags
                               |   dev->l3mdev_ops = NULL;
                               |
      visit master->l3mdev_ops |

To avoid this by do not set dev->l3mdev_ops when unregister l3s ipvlan.

Suggested-by: David Ahern <dsahern@xxxxxxxxxx>
Fixes: c675e06a98a4 ("ipvlan: decouple l3s mode dependencies from other modes")
Signed-off-by: Wang Liang <wangliang74@xxxxxxxxxx>
---
 drivers/net/ipvlan/ipvlan_l3s.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/net/ipvlan/ipvlan_l3s.c b/drivers/net/ipvlan/ipvlan_l3s.c
index b4ef386bdb1b..7c017fe35522 100644
--- a/drivers/net/ipvlan/ipvlan_l3s.c
+++ b/drivers/net/ipvlan/ipvlan_l3s.c
@@ -226,5 +226,4 @@ void ipvlan_l3s_unregister(struct ipvl_port *port)
 
 	dev->priv_flags &= ~IFF_L3MDEV_RX_HANDLER;
 	ipvlan_unregister_nf_hook(read_pnet(&port->pnet));
-	dev->l3mdev_ops = NULL;
 }
-- 
2.34.1