6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet [ Upstream commit cd5dd68267c4238795fadaf02b3575ca3f8a6500 ] Callers that only reserve ETH_HLEN or less (such as llc_alloc_frame()), or skbs allocated before dynamic device/headroom changes (e.g. toggling VLAN_FLAG_REORDER_HDR or bonding/team switching slaves), can reach vlan_dev_hard_header() with insufficient headroom and trigger skb_under_panic(). Use skb_cow_head() in vlan_dev_hard_header() when VLAN_FLAG_REORDER_HDR is not set to ensure sufficient headroom for the VLAN header(s) and the underlying device hard header. Use READ_ONCE() to read dev->hard_header_len and dev->needed_headroom as they can be updated concurrently under RTNL (e.g. in vlan_transfer_features()) while vlan_dev_hard_header() runs locklessly on the transmit path. Also avoid LL_RESERVED_SPACE(dev) here so that the extra HH_DATA_MOD alignment padding does not trigger unnecessary pskb_expand_head() reallocations on inner stacked VLAN devices after the outer VLAN header has been pushed. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: Zixuan Chai Closes: https://lore.kernel.org/netdev/cover.1789987105.git.petalzu987@gmail.com/ Link: https://lore.kernel.org/netdev/179022851638.2160803.1808206741379444999@kernel.org/ Cc: Hangbin Liu Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260924082951.1599377-5-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/8021q/vlan_dev.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c index 560521cf596e3..618c8617c2c43 100644 --- a/net/8021q/vlan_dev.c +++ b/net/8021q/vlan_dev.c @@ -55,6 +55,11 @@ static int vlan_dev_hard_header(struct sk_buff *skb, struct net_device *dev, int rc; if (!(vlan->flags & VLAN_FLAG_REORDER_HDR)) { + unsigned int hlen = READ_ONCE(dev->hard_header_len) + + READ_ONCE(dev->needed_headroom); + + if (skb_cow_head(skb, hlen) < 0) + return -ENOMEM; vhdr = skb_push(skb, VLAN_HLEN); vlan_tci = vlan->vlan_id; -- 2.53.0