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

[Simon Horman <horms@kernel.org>]

On Fri, Mar 21, 2025 at 05:03:53PM +0800, Wang Liang wrote:
> 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@kernel.org>
> Fixes: c675e06a98a4 ("ipvlan: decouple l3s mode dependencies from other modes")
> Signed-off-by: Wang Liang <wangliang74@huawei.com>

Reviewed-by: Simon Horman <horms@kernel.org>