CVE-2026-74743

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

macvlan: inherit neededheadroom and neededtailroom from lowerdev

macvlan devices inherit hardheaderlen from lowerdev during macvlaninit(), but leave neededheadroom and needed_tailroom set to 0.

When the underlying lowerdev requires extra headroom or tailroom for headers/trailers (e.g. macsec, ipsec, wireguard, tunnels, or veth with rx headroom), upper layers calculating packet headroom and tailroom fail to reserve sufficient space.

This can result in reallocation overhead, skb headroom underflows, or KASAN slab-use-after-free crashes when devhardheader() / macvlanhardheader() prepends header data or when lower devices append tailroom.

Fix this by: 1. Inheriting neededheadroom and neededtailroom from lowerdev in macvlaninit(). 2. Propagating neededheadroom and neededtailroom updates to attached macvlans in macvlandeviceevent() when receiving NETDEVFEAT_CHANGE events.