CVE-2026-80925vlan: fix skb_under_panic and races when toggling HW VLAN offload

Official description

In the Linux kernel, the following vulnerability has been resolved: vlan: fix skb_under_panic and races when toggling HW VLAN offload Toggling hardware VLAN TX offload (NETIF_F_HW_VLAN_CTAG_TX or NETIF_F_HW_VLAN_STAG_TX) on a lower device invokes vlan_transfer_features(), which dynamically changed vlandev->hard_header_len. This causes two issues: 1. Lockless TX paths (e.g. packet_snd in af_packet.c, ip6_finish_output2) read dev->hard_header_len without holding RTNL lock. Mutating hard_header_len dynamically under RTNL creates a data race where upper layers reserve insufficient headroom based on a stale hard_header_len, resulting in skb_under_panic when vlan_dev_hard_header() is called. 2. In addition, vlan_transfer_features() updated hard_header_len without updating header_ops, causing a mismatch between allocated headroom and header creation. Always setting dev->hard_header_len = real_dev->hard_header_len and dev->needed_headroom = real_dev->needed_headroom + VLAN_HLEN unconditionally ensures: - dev->hard_header_len remains 100% static and immutable at real_dev->hard_header_len, eliminating all dynamic runtime updates and data races on hard_header_len. - Upper layers allocating skbs via LL_RESERVED_SPACE() will always reserve sufficient headroom for software VLAN tag insertion (real_dev->hard_header_len + real_dev->needed_headroom + VLAN_HLEN). - vlandev inherits real_dev->needed_tailroom so underlying trailer/padding/ICV requirements are honored. - AF_PACKET SOCK_RAW network header offsets remain correctly aligned at real_dev->hard_header_len. - vlan_header_ops is used unconditionally. Note to stable teams: Make sure to backport these commits: e16e960d55a4 ("ipvlan: inherit needed_headroom and needed_tailroom from phy_dev") cef51860becd ("macvlan: inherit needed_headroom and needed_tailroom from lowerdev")

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/69f2fc6e761ee68a4c0c8e416ae88c573d4d7319
• https://git.kernel.org/stable/c/b38d7a4bc9c17e1d437696da25f9fbc286614d9d
• https://git.kernel.org/stable/c/b30fe4de285b9bdaf9508740191f69f7cd83b8fa
• https://git.kernel.org/stable/c/1517d1996b5236fe69eccd9d253f725e06996eb1
• https://git.kernel.org/stable/c/a29f3b884ba50217e6f50414f568073221e2bb07
• https://git.kernel.org/stable/c/447cbe95ebb95392b5d8f6a01c0556826919ce23