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 changes 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. A VLAN interface may require software VLAN header insertion at any point (e.g., if reorder_hdr is disabled or HW offload is unavailable). Always setting hard_header_len = real_dev->hard_header_len + VLAN_HLEN and using vlan_header_ops unconditionally ensures sufficient headroom is reserved by all upper layers and avoids any data race on hard_header_len during ETHTOOL feature changes. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: Tangxin Xie Closes: https://lore.kernel.org/netdev/99d678ae-c7b2-4b44-b534-b8320679deb3@h-partners.com/ Signed-off-by: Eric Dumazet --- net/8021q/vlan_dev.c | 34 +++------------------------------- 1 file changed, 3 insertions(+), 31 deletions(-) diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c index ec2569b3f8dac629027b4344bc89402decf026d1..acf7f52d1eb2191ec0387dc29e2e9eb34124aa9d 100644 --- a/net/8021q/vlan_dev.c +++ b/net/8021q/vlan_dev.c @@ -502,26 +502,6 @@ static const struct header_ops vlan_header_ops = { .parse_protocol = vlan_parse_protocol, }; -static int vlan_passthru_hard_header(struct sk_buff *skb, struct net_device *dev, - unsigned short type, - const void *daddr, const void *saddr, - unsigned int len) -{ - struct vlan_dev_priv *vlan = vlan_dev_priv(dev); - struct net_device *real_dev = vlan->real_dev; - - if (saddr == NULL) - saddr = dev->dev_addr; - - return dev_hard_header(skb, real_dev, type, daddr, saddr, len); -} - -static const struct header_ops vlan_passthru_header_ops = { - .create = vlan_passthru_hard_header, - .parse = eth_header_parse, - .parse_protocol = vlan_parse_protocol, -}; - static const struct device_type vlan_type = { .name = "vlan", }; @@ -581,13 +561,8 @@ static int vlan_dev_init(struct net_device *dev) #endif dev->needed_headroom = real_dev->needed_headroom; - if (vlan_hw_offload_capable(real_dev->features, vlan->vlan_proto)) { - dev->header_ops = &vlan_passthru_header_ops; - dev->hard_header_len = real_dev->hard_header_len; - } else { - dev->header_ops = &vlan_header_ops; - dev->hard_header_len = real_dev->hard_header_len + VLAN_HLEN; - } + dev->header_ops = &vlan_header_ops; + dev->hard_header_len = real_dev->hard_header_len + VLAN_HLEN; dev->netdev_ops = &vlan_netdev_ops; @@ -1029,10 +1004,7 @@ static void vlan_transfer_features(struct net_device *dev, 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; + vlandev->hard_header_len = dev->hard_header_len + VLAN_HLEN; #if IS_ENABLED(CONFIG_FCOE) vlandev->fcoe_ddp_xid = dev->fcoe_ddp_xid; -- 2.55.0.229.g6434b31f56-goog