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

[Simon Horman <horms@kernel.org>]

On Wed, Mar 19, 2025 at 10:07:03AM +0800, Wang Liang wrote:
> 
> 在 2025/3/18 23:02, David Ahern 写道:
> > 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.
> 
> Thanks.
> 
> Only l3s ipvlan set the dev->l3mdev_ops to NULL at present, I will delete
> 'dev->l3mdev_ops = NULL' in ipvlan_l3s_unregister(), is that ok?

TBH, I am somewhat unclear on the correct tear down behaviour.
But I also understood that to be David's suggestion.
And I think that implementing that, and posting it as v2 would
be a good next step.