From 72b5b9a28b996e09b8b5b944370c79851bb68f52 Mon Sep 17 00:00:00 2001 From: Zixuan Chai Date: Thu, 24 Sep 2026 09:26:05 +0800 Subject: [PATCH] llc: reserve device headroom for allocated frames llc_alloc_frame() reserves link-layer headroom using the device type. This is insufficient for stacked Ethernet devices such as VLAN devices, where vlan_dev_hard_header() pushes a VLAN header before the lower device's Ethernet header. An LLC response on such a device can therefore underflow skb headroom in eth_header(). Use LL_RESERVED_SPACE() to account for the device's actual required headroom while preserving the existing LLC device-type check. Fixes: bf9ae5386bca ("llc: use dev_hard_header") Cc: stable@vger.kernel.org Reported-by: VEGA Signed-off-by: Zixuan Chai Signed-off-by: Ren Wei Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260924012613.2533934-1-weir@nebusec.ai Signed-off-by: Jakub Kicinski --- net/llc/llc_sap.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/llc/llc_sap.c b/net/llc/llc_sap.c index 1bd446a21092..3904a1b4ba84 100644 --- a/net/llc/llc_sap.c +++ b/net/llc/llc_sap.c @@ -19,12 +19,12 @@ #include #include -static int llc_mac_header_len(unsigned short devtype) +static int llc_mac_header_len(struct net_device *dev) { - switch (devtype) { + switch (dev->type) { case ARPHRD_ETHER: case ARPHRD_LOOPBACK: - return sizeof(struct ethhdr); + return LL_RESERVED_SPACE(dev); } return 0; } @@ -45,7 +45,7 @@ struct sk_buff *llc_alloc_frame(struct sock *sk, struct net_device *dev, int hlen = type == LLC_PDU_TYPE_U ? 3 : 4; struct sk_buff *skb; - hlen += llc_mac_header_len(dev->type); + hlen += llc_mac_header_len(dev); skb = alloc_skb(hlen + data_size, GFP_ATOMIC); if (skb) {