[PATCH net] macvlan: inherit needed_headroom and needed_tailroom from lowerdev

[PATCH net] macvlan: inherit needed_headroom and needed_tailroom from lowerdev

[Eric Dumazet]

macvlan devices inherit hard_header_len from lowerdev during macvlan_init(),
but leave needed_headroom and needed_tailroom set to 0.

When the underlying lowerdev 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() / macvlan_hard_header()
prepends header data or when lower devices append tailroom.

Fix this by:
1. Inheriting needed_headroom and needed_tailroom from lowerdev in macvlan_init().
2. Propagating needed_headroom and needed_tailroom updates to attached macvlans
   in macvlan_device_event() when receiving NETDEV_FEAT_CHANGE events.

Fixes: b863ceb7ddce ("[NET]: Add macvlan driver")
Reported-by: Tangxin Xie <xietangxin@h-partners.com>
Closes: https://lore.kernel.org/netdev/CANn89i+1EW-sFNK8xoq98gMbPCeLS7e=+rs9gHfLg5Wj+4x0sw@mail.gmail.com/T/#m16adf0ff972cbfd8066c3a8e656e75eaeb12d021
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 drivers/net/macvlan.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index c40fa331836bb2395267914807542ae5094e1a3c..ff2f4bb651b74cdb054f245ea0f4e8cfe2297193 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -950,6 +950,8 @@ static int macvlan_init(struct net_device *dev)
 	dev->lltx		= true;
 	netif_inherit_tso_max(dev, lowerdev);
 	dev->hard_header_len	= lowerdev->hard_header_len;
+	dev->needed_headroom	= lowerdev->needed_headroom;
+	dev->needed_tailroom	= lowerdev->needed_tailroom;
 	macvlan_set_lockdep_class(dev);
 
 	vlan->pcpu_stats = netdev_alloc_pcpu_stats(struct vlan_pcpu_stats);
@@ -1824,6 +1826,8 @@ static int macvlan_device_event(struct notifier_block *unused,
 	case NETDEV_FEAT_CHANGE:
 		list_for_each_entry(vlan, &port->vlans, list) {
 			netif_inherit_tso_max(vlan->dev, dev);
+			vlan->dev->needed_headroom = dev->needed_headroom;
+			vlan->dev->needed_tailroom = dev->needed_tailroom;
 			netdev_update_features(vlan->dev);
 		}
 		break;
-- 
2.55.0.629.g250fe7f194-goog

Re: [PATCH net] macvlan: inherit needed_headroom and needed_tailroom from lowerdev

[Hangbin Liu]

On 06.08.2026 14:19, Eric Dumazet wrote:
>macvlan devices inherit hard_header_len from lowerdev during macvlan_init(),
>but leave needed_headroom and needed_tailroom set to 0.
>
>When the underlying lowerdev 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() / macvlan_hard_header()
>prepends header data or when lower devices append tailroom.
>
>Fix this by:
>1. Inheriting needed_headroom and needed_tailroom from lowerdev in macvlan_init().
>2. Propagating needed_headroom and needed_tailroom updates to attached macvlans
>   in macvlan_device_event() when receiving NETDEV_FEAT_CHANGE events.
>
>Fixes: b863ceb7ddce ("[NET]: Add macvlan driver")
>Reported-by: Tangxin Xie <xietangxin@h-partners.com>
>Closes: https://lore.kernel.org/netdev/CANn89i+1EW-sFNK8xoq98gMbPCeLS7e=+rs9gHfLg5Wj+4x0sw@mail.gmail.com/T/#m16adf0ff972cbfd8066c3a8e656e75eaeb12d021
>Signed-off-by: Eric Dumazet <edumazet@google.com>
>---
> drivers/net/macvlan.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
>diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
>index c40fa331836bb2395267914807542ae5094e1a3c..ff2f4bb651b74cdb054f245ea0f4e8cfe2297193 100644
>--- a/drivers/net/macvlan.c
>+++ b/drivers/net/macvlan.c
>@@ -950,6 +950,8 @@ static int macvlan_init(struct net_device *dev)
> 	dev->lltx		= true;
> 	netif_inherit_tso_max(dev, lowerdev);
> 	dev->hard_header_len	= lowerdev->hard_header_len;
>+	dev->needed_headroom	= lowerdev->needed_headroom;
>+	dev->needed_tailroom	= lowerdev->needed_tailroom;
> 	macvlan_set_lockdep_class(dev);
>
> 	vlan->pcpu_stats = netdev_alloc_pcpu_stats(struct vlan_pcpu_stats);
>@@ -1824,6 +1826,8 @@ static int macvlan_device_event(struct notifier_block *unused,
> 	case NETDEV_FEAT_CHANGE:
> 		list_for_each_entry(vlan, &port->vlans, list) {
> 			netif_inherit_tso_max(vlan->dev, dev);
>+			vlan->dev->needed_headroom = dev->needed_headroom;
>+			vlan->dev->needed_tailroom = dev->needed_tailroom;
> 			netdev_update_features(vlan->dev);
> 		}
> 		break;
>-- 
>2.55.0.629.g250fe7f194-goog
>

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