CVE-2026-97612net: mpls: clear inner_protocol when the last label is popped

Official description

In the Linux kernel, the following vulnerability has been resolved: net: mpls: clear inner_protocol when the last label is popped skb_mpls_push() records the pre-encapsulation network header once, gated on !skb->inner_protocol. skb_mpls_pop() never clears that record, so it outlives the encapsulation it describes. Open vSwitch can then re-push MPLS onto a packet whose inner_network_header still points at the older, deeper offset: push a label, pop every label, recirculate (ovs_flow_key_update() re-derives key->eth.type and resets network_header, but leaves inner_*), then push again. ovs_fragment() trusts the record: skb->network_header = skb->inner_network_header; so skb_network_offset() goes negative. The bound check is signed: if (skb_network_offset(skb) > MAX_L2_LEN) a negative offset passes it, and prepare_frag() widens the value: unsigned int hlen = skb_network_offset(skb); memcpy(&data->l2_data, skb->data, hlen); which is a ~4GiB memcpy out of a 30-byte per-CPU buffer. Reproduced on v7.3-rc1. RDX is the truncated length, (unsigned int)(-8): BUG: unable to handle page fault for address: ffffe8ffffc16000 #PF: supervisor write access in kernel mode Oops: 0002 [#1] SMP KASAN NOPTI RIP: 0010:memcpy+0x8/0x20 RDX: 00000000fffffff8 RSI: ffff888105d732db RDI: ffffe8ffffc16000 prepare_frag+0x3df/0x4e0 ovs_fragment+0x589/0x7e0 do_output+0x4ce/0x5e0 do_execute_actions+0x55d2/0x7b30 ovs_execute_actions+0xea/0x450 Same root-cause shape as commit 975b5b067f52 ("ipv6: sr: restore network header before routing and forwarding"): a stale network header offset reaching a consumer that widens it. Here it originates in the MPLS push/pop path. Clear inner_protocol once the packet is no longer MPLS, so a later push re-records the current header. net/sched/act_mpls.c is the only other skb_mpls_pop() caller and gets the same fix; sch_frag.c saves and restores inner_protocol around fragmentation in the same way OVS does.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/55ed97db27bffe29c21fdefd5d25601322c36ff8
• https://git.kernel.org/stable/c/833ec2788322306407503b4cfc7745cd1f9d785f
• https://git.kernel.org/stable/c/38db09804b2616aa1e2fcdf97f0c3ae8b9dbdd34
• https://git.kernel.org/stable/c/0b3425fd0ecd515997956f7bb8a8a576b444ed64
• https://git.kernel.org/stable/c/011e17b5cae19b9f6a150923275e41c278de64f0
• https://git.kernel.org/stable/c/da8c3a7f5d3137fec4ff60a6248f5f6d66b6a63e
• https://git.kernel.org/stable/c/b39120523475d6b436be7f6cb27d48064148a327
• https://git.kernel.org/stable/c/78a86d75a70e1e227711c72865c59b1422d0a5ae