On Monday, 19 May 2025 22:46:31 CEST Matthias Schiffer wrote:
> struct batadv_hard_iface *
> -batadv_hardif_get_by_netdev(const struct net_device *net_dev)
> +batadv_hardif_get_by_netdev(struct net_device *net_dev)
> {
> struct batadv_hard_iface *hard_iface;
> + struct net_device *mesh_iface;
>
> - rcu_read_lock();
> - list_for_each_entry_rcu(hard_iface, &batadv_hardif_list, list) {
> - if (hard_iface->net_dev == net_dev &&
> - kref_get_unless_zero(&hard_iface->refcount))
> - goto out;
> - }
> + mesh_iface = netdev_master_upper_dev_get(net_dev);
> + if (!mesh_iface || !batadv_meshif_is_valid(mesh_iface))
> + return NULL;
>
> - hard_iface = NULL;
> + hard_iface = netdev_lower_dev_get_private(mesh_iface, net_dev);
> + if (!kref_get_unless_zero(&hard_iface->refcount))
> + return NULL;
>
> -out:
> - rcu_read_unlock();
> return hard_iface;
> }
This code is now relying on rtnl_lock() (see `ASSERT_RTNL` in
`netdev_master_upper_dev_get` and most likely some comments somwhere about the
lists used by `netdev_lower_dev_get_private`). But `batadv_tt_local_add` is
using this function without holding this lock all the time. For example during
packet processing.
See for example `batadv_tt_local_add` calls in `batadv_interface_tx`. This
will happen when `skb->skb_iif` is not 0 (so it was forwarded).
Please double check this - I have not actually tested it but just went through
the code.
And saying this, the `batadv_hardif_get_by_netdev` call was also used to
retrieve additional information about alll kind of interfaces - even when they
are not used by batman-adv directly. For example for figuring out if it is a
wifi interface(for the TT wifi flag). With you change here, you are basically
breaking this functionality because you now require that the netdev is a lower
interface of batman-adv. Therefore, things like:
┌──────┐
┌───────────┼br-lan├──────┐
│ └──────┘ │
│ │
│ │
┌─▼─┐ ┌──▼─┐
│ap0│ │bat0│
└───┘ └──┬─┘
│
│
┌──▼──┐
│mesh0│
└─────┘
Is not handled anymore correctly in TT because ap0 is not a lower interface of
any batadv mesh interface. And as result, the ap-isolation feature of TT
will break.
Kind regards,
Sven
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