CVE-2026-74744

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

ipvlan: inherit neededheadroom and neededtailroom from phy_dev

ipvlan devices inherit hardheaderlen from phydev during ipvlaninit(),

but leave neededheadroom and neededtailroom set to 0.

When the underlying phy_dev (or stacked lower device) 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() / ipvlanhardheader()

prepends header data or when lower devices append tailroom.

Fix this by:

1. Inheriting neededheadroom and neededtailroom from phydev in ipvlaninit().
2. Propagating neededheadroom and neededtailroom updates to attached ipvlans

   in ipvlandeviceevent() when receiving NETDEVFEATCHANGE events.