CVE-2026-98554

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

vlan: ensure sufficient headroom in vlan_dev_hard_header()

Callers that only reserve ETH_HLEN or less (such as llc_alloc_frame()),

or skbs allocated before dynamic device/headroom changes (e.g. toggling

VLAN_FLAG_REORDER_HDR or bonding/team switching slaves), can reach

vlan_dev_hard_header() with insufficient headroom and trigger

skb_under_panic().

Use skb_cow_head() in vlan_dev_hard_header() when VLAN_FLAG_REORDER_HDR

is not set to ensure sufficient headroom for the VLAN header(s) and the

underlying device hard header.

Use READ_ONCE() to read dev->hard_header_len and dev->needed_headroom as

they can be updated concurrently under RTNL (e.g. in

vlan_transfer_features()) while vlan_dev_hard_header() runs locklessly on

the transmit path. Also avoid LL_RESERVED_SPACE(dev) here so that the

extra HH_DATA_MOD alignment padding does not trigger unnecessary

pskb_expand_head() reallocations on inner stacked VLAN devices after the

outer VLAN header has been pushed.