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

[David Ahern <dsahern@kernel.org>]

On 3/18/25 3:38 PM, Simon Horman wrote:
> On Thu, Mar 13, 2025 at 09:27:13AM +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 |
>>
>> Add lock for dev->priv_flags and dev->l3mdev_ops is too expensive. Resolve
>> this issue by add check for master->l3mdev_ops.
> 
> Hi Wang Liang,
> 
> It seems to me that checking master->l3mdev_ops like this is racy.

vrf device leaves the l3mdev ops set; that is probably the better way to go.