[PATCH] net/packet: fix network header offset for non-VLAN raw packets on VLAN subinterfaces

[Junnan Zhang <zhangjn_dev@163.com>]

From: Junnan Zhang <zhangjn11@chinatelecom.cn>

AF_PACKET SOCK_RAW reserves dev->hard_header_len bytes of headroom. For
VLAN subinterfaces, hard_header_len includes VLAN tag space (18 bytes)
while min_header_len is the real Ethernet header length (14 bytes). When
userspace sends a standard untagged Ethernet frame through a VLAN
subinterface, packet_parse_headers() only corrects network_header for
VLAN-tagged frames. For non-VLAN frames it leaves network_header at
hard_header_len, so the IP header is found 4 bytes too late and
inet_gso_segment() fails with -EINVAL.

Set network_header to min_header_len for non-VLAN SOCK_RAW frames on
Ethernet devices whose hard_header_len exceeds min_header_len, so the
L3/L4 header positions match the actual on-the-wire frame.

This fix is placed before skb_probe_transport_header() so that both the
transport header probe (which uses skb_network_offset() as nhoff) and
subsequent GSO see the right L3/L4 offsets. It complements
commit 01fdecc0480d ("net: packet: fix wrong transport_header when sending VLAN-tagged frame")
which only covers VLAN-tagged frames.

Fixes: dfed913e8b55 ("net/af_packet: add VLAN support for AF_PACKET SOCK_RAW GSO")
Signed-off-by: Junnan Zhang <zhangjn11@chinatelecom.cn>
Signed-off-by: Shouxin Sun <sunshx@chinatelecom.cn>
Signed-off-by: Junnan Zhang <zhangjn_dev@163.com>
---
 net/packet/af_packet.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 1168bd6b09cd..4669320f551b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1935,6 +1935,7 @@ static int packet_rcv_spkt(struct sk_buff *skb, struct net_device *dev,
 static void packet_parse_headers(struct sk_buff *skb, struct socket *sock)
 {
 	int depth;
+	bool has_vlan;
 
 	/* On TX skb->data is the L2 header; anchor it for all socket types. */
 	skb_reset_mac_header(skb);
@@ -1943,11 +1944,23 @@ static void packet_parse_headers(struct sk_buff *skb, struct socket *sock)
 	    sock->type == SOCK_RAW)
 		skb->protocol = dev_parse_header_protocol(skb);
 
+	has_vlan = likely(skb->dev->type == ARPHRD_ETHER) &&
+		   eth_type_vlan(skb->protocol);
+
+	/* For non-VLAN raw frames on devices whose hard_header_len includes
+	 * VLAN tag space (e.g. VLAN subinterfaces), the network header must be
+	 * at the actual L2/L3 boundary, not hard_header_len, so that both the
+	 * transport header probe below and subsequent GSO see the right L3.
+	 */
+	if (!has_vlan && sock->type == SOCK_RAW &&
+	    likely(skb->dev->type == ARPHRD_ETHER) &&
+	    skb->dev->min_header_len < skb->dev->hard_header_len)
+		skb_set_network_header(skb, skb->dev->min_header_len);
+
 	skb_probe_transport_header(skb);
 
 	/* Move network header to the right position for VLAN tagged packets */
-	if (likely(skb->dev->type == ARPHRD_ETHER) &&
-	    eth_type_vlan(skb->protocol) &&
+	if (has_vlan &&
 	    vlan_get_protocol_and_depth(skb, skb->protocol, &depth) != 0)
 		skb_set_network_header(skb, depth);
 }
-- 
2.43.0