6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jakub Kicinski [ Upstream commit cd1c188db1091991fc1d7f565824d077d659425b ] vlan_device_event() generates nested UP/DOWN, MTU and feature change events. It executes an event for the VLAN device directly from the notifier - while the locks of the lower device are held. This causes deadlocks, for example: bond (3) bond_update_speed_duplex(vlan) | ^ v vlan (2) UP(vlan) (4) vlan_ethtool_get_link_ksettings() | ^ v dummy (1) UP(dummy) (5) __ethtool_get_link_ksettings() The dummy device is ops locked, vlan creates a nested event (2), then bond wants to ask vlan for link state (3). bond uses the "I'm already holding the instance lock" flavor of API. But in this case the lock held refers to vlan itself. We hit vlan's link settings trampoline (4) and call __ethtool_get_link_ksettings() which tries to lock dummy. Deadlock. There's no clean way for us to tell the vlan_ethtool_get_link_ksettings() that the caller is already in lower device's critical section. Defer the propagation to the per-netdev work facility instead: the notifier only schedules netdev_work_sched(vlandev, VLAN_WORK_*), and ndo_work (vlan_dev_work) applies the change later. Hopefully nobody expects the VLAN state changes to be instantaneous. If someone does expect the changes to be instantaneous we will have to do the same thing Stan did for rx_mode and "strategically" place sync calls, to make sure such delayed works are executed after we drop the ops lock but before we drop rtnl_lock. Stan suggests that if we need that down the line we may consider reshaping the mechanism into "async notifications". AFAICT only vlan does this sort of netdev open chaining, so as a first try I think that sticking the complexity into the vlan code makes sense. One corner case is that we need to cancel the event if user explicitly changes the state before work could run. Consider the following operations with vlan0 on top of dummy0: ip link set dev dummy0 up # queues work to up vlan0 ip link set dev vlan0 down # user explicitly downs the vlan ndo_work # acts on the stale event Reported-by: syzbot+09da62a8b78959ceb8bb@syzkaller.appspotmail.com Reported-by: syzbot+cb67c392b0b8f0fd0fc1@syzkaller.appspotmail.com Reported-by: syzbot+9bb8bd77f3966641f298@syzkaller.appspotmail.com Fixes: 9f275c2e9020 ("net: ethtool: make sure __ethtool_get_link_ksettings() is ops-locked") Reviewed-by: Kuniyuki Iwashima Reviewed-by: Nicolai Buchwitz Acked-by: Stanislav Fomichev Link: https://patch.msgid.link/20260624182018.2445732-4-kuba@kernel.org Signed-off-by: Jakub Kicinski [ sashal: Reduced backport -- upstream cd1c188db1091 touches 5 file(s), this backport carries 3. Not backported here: Documentation/networking/netdevices.rst net/core/dev.c This note is generated from the file lists only; see the resolution record for the reasoning. ] Stable-dep-of: 447cbe95ebb9 ("vlan: fix skb_under_panic and races when toggling HW VLAN offload") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- net/8021q/vlan.c | 23 ----------------------- net/8021q/vlan.h | 2 ++ net/8021q/vlan_dev.c | 25 ++++++++++++++++++++++++- 3 files changed, 26 insertions(+), 24 deletions(-) --- a/net/8021q/vlan.c +++ b/net/8021q/vlan.c @@ -317,29 +317,6 @@ out: ether_addr_copy(vlan->real_dev_addr, dev->dev_addr); } -static void vlan_transfer_features(struct net_device *dev, - struct net_device *vlandev) -{ - struct vlan_dev_priv *vlan = vlan_dev_priv(vlandev); - - netif_inherit_tso_max(vlandev, dev); - - if (vlan_hw_offload_capable(dev->features, vlan->vlan_proto)) - vlandev->hard_header_len = dev->hard_header_len; - else - vlandev->hard_header_len = dev->hard_header_len + VLAN_HLEN; - -#if IS_ENABLED(CONFIG_FCOE) - vlandev->fcoe_ddp_xid = dev->fcoe_ddp_xid; -#endif - - vlandev->priv_flags &= ~IFF_XMIT_DST_RELEASE; - vlandev->priv_flags |= (vlan->real_dev->priv_flags & IFF_XMIT_DST_RELEASE); - vlandev->hw_enc_features = vlan_tnl_features(vlan->real_dev); - - netdev_update_features(vlandev); -} - static int __vlan_device_event(struct net_device *dev, unsigned long event) { int err = 0; --- a/net/8021q/vlan.h +++ b/net/8021q/vlan.h @@ -126,6 +126,8 @@ int vlan_filter_push_vids(struct vlan_in void vlan_filter_drop_vids(struct vlan_info *vlan_info, __be16 proto); /* found in vlan_dev.c */ +void vlan_transfer_features(struct net_device *dev, + struct net_device *vlandev); void vlan_dev_set_ingress_priority(const struct net_device *dev, u32 skb_prio, u16 vlan_prio); int vlan_dev_set_egress_priority(const struct net_device *dev, --- a/net/8021q/vlan_dev.c +++ b/net/8021q/vlan_dev.c @@ -541,7 +541,7 @@ static const struct header_ops vlan_pass .parse_protocol = vlan_parse_protocol, }; -static struct device_type vlan_type = { +static const struct device_type vlan_type = { .name = "vlan", }; @@ -1046,6 +1046,29 @@ static const struct ethtool_ops vlan_eth .get_ts_info = vlan_ethtool_get_ts_info, }; +void vlan_transfer_features(struct net_device *dev, + struct net_device *vlandev) +{ + struct vlan_dev_priv *vlan = vlan_dev_priv(vlandev); + + netif_inherit_tso_max(vlandev, dev); + + if (vlan_hw_offload_capable(dev->features, vlan->vlan_proto)) + vlandev->hard_header_len = dev->hard_header_len; + else + vlandev->hard_header_len = dev->hard_header_len + VLAN_HLEN; + +#if IS_ENABLED(CONFIG_FCOE) + vlandev->fcoe_ddp_xid = dev->fcoe_ddp_xid; +#endif + + vlandev->priv_flags &= ~IFF_XMIT_DST_RELEASE; + vlandev->priv_flags |= (vlan->real_dev->priv_flags & IFF_XMIT_DST_RELEASE); + vlandev->hw_enc_features = vlan_tnl_features(vlan->real_dev); + + netdev_update_features(vlandev); +} + static const struct net_device_ops vlan_netdev_ops = { .ndo_change_mtu = vlan_dev_change_mtu, .ndo_init = vlan_dev_init,