CVE-2024-35839 Affecting kernel-rt package, versions <0:5.14.0-427.33.1.el9_4

Note: Versions mentioned in the description apply only to the upstream kernel-rt package and not the kernel-rt package as distributed by AlmaLinux. See How to fix? for AlmaLinux:9 relevant fixed versions and status.

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.

• https://errata.almalinux.org/9/ALSA-2024-5928.html
• https://errata.almalinux.org/8/ALSA-2024-8856.html
• https://access.redhat.com/security/cve/CVE-2024-35839
• https://access.redhat.com/errata/RHSA-2024:5928
• https://access.redhat.com/errata/RHSA-2024:8856
• https://git.kernel.org/stable/c/544add1f1cfb78c3dfa3e6edcf4668f6be5e730c
• https://git.kernel.org/stable/c/7ae19ee81ca56b13c50a78de6c47d5b8fdc9d97b
• https://git.kernel.org/stable/c/9325e3188a9cf3f69fc6f32af59844bbc5b90547
• https://git.kernel.org/stable/c/9874808878d9eed407e3977fd11fee49de1e1d86