[Patch net] wireguard: preserve skb->mark on ingress side

[Cong Wang]

From: Cong Wang <cong.wang at bytedance.com>

On ingress side, wg_reset_packet() resets skb->mark twice: with
skb_scrub_packet() (xnet==true) and with memset() following it. But
skb->mark does not have to be cleared at least when staying in the
same net namespace, and other tunnels preserve it too similarly,
especially vxlan.

In our use case, we would like to preserve this skb->mark to
distinguish which wireguard device the packets are routed from.

Tested-by: Peilin Ye <peilin.ye at bytedance.com>
Cc: "Jason A. Donenfeld" <Jason at zx2c4.com>
Signed-off-by: Cong Wang <cong.wang at bytedance.com>
---
 drivers/net/wireguard/queueing.h | 9 +++++++--
 drivers/net/wireguard/receive.c  | 2 +-
 drivers/net/wireguard/send.c     | 2 +-
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireguard/queueing.h b/drivers/net/wireguard/queueing.h
index 4ef2944a68bc..3516c1c59df0 100644
--- a/drivers/net/wireguard/queueing.h
+++ b/drivers/net/wireguard/queueing.h
@@ -73,15 +73,20 @@ static inline bool wg_check_packet_protocol(struct sk_buff *skb)
 	return real_protocol && skb->protocol == real_protocol;
 }
 
-static inline void wg_reset_packet(struct sk_buff *skb, bool encapsulating)
+static inline void wg_reset_packet(struct sk_buff *skb, bool encapsulating,
+				   bool xnet)
 {
 	u8 l4_hash = skb->l4_hash;
 	u8 sw_hash = skb->sw_hash;
 	u32 hash = skb->hash;
-	skb_scrub_packet(skb, true);
+	u32 mark;
+
+	skb_scrub_packet(skb, xnet);
+	mark = skb->mark;
 	memset(&skb->headers_start, 0,
 	       offsetof(struct sk_buff, headers_end) -
 		       offsetof(struct sk_buff, headers_start));
+	skb->mark = mark;
 	if (encapsulating) {
 		skb->l4_hash = l4_hash;
 		skb->sw_hash = sw_hash;
diff --git a/drivers/net/wireguard/receive.c b/drivers/net/wireguard/receive.c
index 7dc84bcca261..385b2b60cfd9 100644
--- a/drivers/net/wireguard/receive.c
+++ b/drivers/net/wireguard/receive.c
@@ -476,7 +476,7 @@ int wg_packet_rx_poll(struct napi_struct *napi, int budget)
 		if (unlikely(wg_socket_endpoint_from_skb(&endpoint, skb)))
 			goto next;
 
-		wg_reset_packet(skb, false);
+		wg_reset_packet(skb, false, !net_eq(dev_net(peer->device->dev), dev_net(skb->dev)));
 		wg_packet_consume_data_done(peer, skb, &endpoint);
 		free = false;
 
diff --git a/drivers/net/wireguard/send.c b/drivers/net/wireguard/send.c
index 5368f7c35b4b..c77ef0815c2e 100644
--- a/drivers/net/wireguard/send.c
+++ b/drivers/net/wireguard/send.c
@@ -296,7 +296,7 @@ void wg_packet_encrypt_worker(struct work_struct *work)
 		skb_list_walk_safe(first, skb, next) {
 			if (likely(encrypt_packet(skb,
 					PACKET_CB(first)->keypair))) {
-				wg_reset_packet(skb, true);
+				wg_reset_packet(skb, true, true);
 			} else {
 				state = PACKET_STATE_DEAD;
 				break;
-- 
2.30.2