Re: [PATCH v2 net] ipvlan: inherit needed_headroom and needed_tailroom from phy_dev

[Hangbin Liu <liuhangbin@gmail.com>]

On 06.08.2026 10:38, Eric Dumazet wrote:
>ipvlan devices inherit hard_header_len from phy_dev during ipvlan_init(),
>but leave needed_headroom and needed_tailroom 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 dev_hard_header() / ipvlan_hard_header()
>prepends header data or when lower devices append tailroom.
>
>Fix this by:
>1. Inheriting needed_headroom and needed_tailroom from phy_dev in ipvlan_init().
>2. Propagating needed_headroom and needed_tailroom updates to attached ipvlans
>   in ipvlan_device_event() when receiving NETDEV_FEAT_CHANGE events.
>
>Fixes: 2ad7bfab3016 ("ipvlan: Initial check-in of the IPVLAN driver.")
>Reported-by: syzbot+1f9fd0f4b601cf88d6e6@syzkaller.appspotmail.com
>Closes: https://lore.kernel.org/netdev/6a720a21.40259c87.584f4.04bb.GAE@google.com/T/#u
>Reported-by: Tangxin Xie <xietangxin@h-partners.com>
>Closes: https://lore.kernel.org/netdev/CANn89i+1EW-sFNK8xoq98gMbPCeLS7e=+rs9gHfLg5Wj+4x0sw@mail.gmail.com/T/#mcc6307f115e500df23ea2980d5669fe95f20b6b4
>Signed-off-by: Eric Dumazet <edumazet@google.com>
>---
>v2: also inherit needed_tailroom (Sashiko)
>v1: https://lore.kernel.org/netdev/CANn89iLr4EQxBAKikZCeXbXEk-pjmT4mq3d=D2P01MtNSUgwrg@mail.gmail.com/T/#t
>
> drivers/net/ipvlan/ipvlan_main.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
>diff --git a/drivers/net/ipvlan/ipvlan_main.c b/drivers/net/ipvlan/ipvlan_main.c
>index ed46439a9f4eb1dd8bfaf6c83476ba4f2aff31bc..92d3d340281ffbc8e54a61e975484ab156c42c9b 100644
>--- a/drivers/net/ipvlan/ipvlan_main.c
>+++ b/drivers/net/ipvlan/ipvlan_main.c
>@@ -146,6 +146,8 @@ static int ipvlan_init(struct net_device *dev)
> 	dev->lltx = true;
> 	netif_inherit_tso_max(dev, phy_dev);
> 	dev->hard_header_len = phy_dev->hard_header_len;
>+	dev->needed_headroom = phy_dev->needed_headroom;
>+	dev->needed_tailroom = phy_dev->needed_tailroom;
>
> 	netdev_lockdep_set_classes(dev);
>
>@@ -773,6 +775,8 @@ static int ipvlan_device_event(struct notifier_block *unused,
> 	case NETDEV_FEAT_CHANGE:
> 		list_for_each_entry(ipvlan, &port->ipvlans, pnode) {
> 			netif_inherit_tso_max(ipvlan->dev, dev);
>+			ipvlan->dev->needed_headroom = dev->needed_headroom;
>+			ipvlan->dev->needed_tailroom = dev->needed_tailroom;
> 			netdev_update_features(ipvlan->dev);
> 		}
> 		break;
>-- 
>2.55.0.629.g250fe7f194-goog
>

Reviewed-by: Hangbin Liu <liuhangbin@kylinos.cn>