CVE-2024-35839

In the Linux kernel, the following vulnerability has been resolved:

netfilter: bridge: replace physindev with physinif in nf_bridge_info

An skb can be added to a neigh->arp_queue while waiting for an arp

reply. Where original skb's skb->dev can be different to neigh's

neigh->dev. For instance in case of bridging dnated skb from one veth to

another, the skb would be added to a neigh->arp_queue of the bridge.

As skb->dev can be reset back to nf_bridge->physindev and used, and as

there is no explicit mechanism that prevents this physindev from been

freed under us (for instance neigh_flush_dev doesn't cleanup skbs from

different device's neigh queue) we can crash on e.g. this stack:

arp_process

neigh_update

skb = __skb_dequeue(&neigh->arp_queue)

neigh_resolve_output(..., skb)

...

br_nf_dev_xmit

br_nf_pre_routing_finish_bridge_slow

skb->dev = nf_bridge->physindev

br_handle_frame_finish

Let's use plain ifindex instead of net_device link. To peek into the

original net_device we will use dev_get_by_index_rcu(). Thus either we

get device and are safe to use it or we don't get it and drop skb.