mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-09-18 22:19:30 +02:00
Eric Dumazet
447cbe95eb
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:e16e960d55("ipvlan: inherit needed_headroom and needed_tailroom from phy_dev")cef51860be("macvlan: inherit needed_headroom and needed_tailroom from lowerdev") Fixes:1da177e4c3("Linux-2.6.12-rc2") Reported-by: Tangxin Xie <xietangxin@h-partners.com> Closes: https://lore.kernel.org/netdev/99d678ae-c7b2-4b44-b534-b8320679deb3@h-partners.com/ Cc: <stable@vger.kernel.org> # 3.19:e16e960d55: ipvlan: inherit needed_headroom and needed_tailroom from phy_dev Cc: <stable@vger.kernel.org> # 3.19:cef51860be: macvlan: inherit needed_headroom and needed_tailroom from lowerdev Cc: <stable@vger.kernel.org> # 3.19 Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260811085246.2267779-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>