From: Martin KaFai Lau <kafai@fb.com>
Date: Wed, 2 Mar 2022 11:55:38 -0800
Subject: net: Handle delivery_time in skb->tstamp during network tapping with
 af_packet
Patch-mainline: v5.18-rc1
Git-commit: 27942a15209f564ed8ee2a9e126cb7b105181355
References: jsc#PED-1377

A latter patch will set the skb->mono_delivery_time to flag the skb->tstamp
is used as the mono delivery_time (EDT) instead of the (rcv) timestamp.
skb_clear_tstamp() will then keep this delivery_time during forwarding.

This patch is to make the network tapping (with af_packet) to handle
the delivery_time stored in skb->tstamp.

Regardless of tapping at the ingress or egress,  the tapped skb is
received by the af_packet socket, so it is ingress to the af_packet
socket and it expects the (rcv) timestamp.

When tapping at egress, dev_queue_xmit_nit() is used.  It has already
expected skb->tstamp may have delivery_time,  so it does
skb_clone()+net_timestamp_set() to ensure the cloned skb has
the (rcv) timestamp before passing to the af_packet sk.
This patch only adds to clear the skb->mono_delivery_time
bit in net_timestamp_set().

When tapping at ingress, it currently expects the skb->tstamp is either 0
or the (rcv) timestamp.  Meaning, the tapping at ingress path
has already expected the skb->tstamp could be 0 and it will get
the (rcv) timestamp by ktime_get_real() when needed.

There are two cases for tapping at ingress:

One case is af_packet queues the skb to its sk_receive_queue.
The skb is either not shared or new clone created.  The newly
added skb_clear_delivery_time() is called to clear the
delivery_time (if any) and set the (rcv) timestamp if
needed before the skb is queued to the sk_receive_queue.

Another case, the ingress skb is directly copied to the rx_ring
and tpacket_get_timestamp() is used to get the (rcv) timestamp.
The newly added skb_tstamp() is used in tpacket_get_timestamp()
to check the skb->mono_delivery_time bit before returning skb->tstamp.
As mentioned earlier, the tapping@ingress has already expected
the skb may not have the (rcv) timestamp (because no sk has asked
for it) and has handled this case by directly calling ktime_get_real().

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 include/linux/skbuff.h |   24 ++++++++++++++++++++++++
 net/core/dev.c         |    4 +++-
 net/packet/af_packet.c |    4 +++-
 3 files changed, 30 insertions(+), 2 deletions(-)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3851,6 +3851,22 @@ static inline void skb_set_delivery_time
 	skb->mono_delivery_time = 0;
 }
 
+DECLARE_STATIC_KEY_FALSE(netstamp_needed_key);
+
+/* It is used in the ingress path to clear the delivery_time.
+ * If needed, set the skb->tstamp to the (rcv) timestamp.
+ */
+static inline void skb_clear_delivery_time(struct sk_buff *skb)
+{
+	if (skb->mono_delivery_time) {
+		skb->mono_delivery_time = 0;
+		if (static_branch_unlikely(&netstamp_needed_key))
+			skb->tstamp = ktime_get_real();
+		else
+			skb->tstamp = 0;
+	}
+}
+
 static inline void skb_clear_tstamp(struct sk_buff *skb)
 {
 	if (skb->mono_delivery_time)
@@ -3859,6 +3875,14 @@ static inline void skb_clear_tstamp(stru
 	skb->tstamp = 0;
 }
 
+static inline ktime_t skb_tstamp(const struct sk_buff *skb)
+{
+	if (skb->mono_delivery_time)
+		return 0;
+
+	return skb->tstamp;
+}
+
 static inline u8 skb_metadata_len(const struct sk_buff *skb)
 {
 	return skb_shinfo(skb)->meta_len;
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1996,7 +1996,8 @@ void net_dec_egress_queue(void)
 EXPORT_SYMBOL_GPL(net_dec_egress_queue);
 #endif
 
-static DEFINE_STATIC_KEY_FALSE(netstamp_needed_key);
+DEFINE_STATIC_KEY_FALSE(netstamp_needed_key);
+EXPORT_SYMBOL(netstamp_needed_key);
 #ifdef CONFIG_JUMP_LABEL
 static atomic_t netstamp_needed_deferred;
 static atomic_t netstamp_wanted;
@@ -2057,6 +2058,7 @@ EXPORT_SYMBOL(net_disable_timestamp);
 static inline void net_timestamp_set(struct sk_buff *skb)
 {
 	skb->tstamp = 0;
+	skb->mono_delivery_time = 0;
 	if (static_branch_unlikely(&netstamp_needed_key))
 		__net_timestamp(skb);
 }
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -424,7 +424,7 @@ static __u32 tpacket_get_timestamp(struc
 		return TP_STATUS_TS_RAW_HARDWARE;
 
 	if ((flags & SOF_TIMESTAMPING_SOFTWARE) &&
-	    ktime_to_timespec64_cond(skb->tstamp, ts))
+	    ktime_to_timespec64_cond(skb_tstamp(skb), ts))
 		return TP_STATUS_TS_SOFTWARE;
 
 	return 0;
@@ -2159,6 +2159,7 @@ static int packet_rcv(struct sk_buff *sk
 	spin_lock(&sk->sk_receive_queue.lock);
 	po->stats.stats1.tp_packets++;
 	sock_skb_set_dropcount(sk, skb);
+	skb_clear_delivery_time(skb);
 	__skb_queue_tail(&sk->sk_receive_queue, skb);
 	spin_unlock(&sk->sk_receive_queue.lock);
 	sk->sk_data_ready(sk);
@@ -2340,6 +2341,7 @@ static int tpacket_rcv(struct sk_buff *s
 	po->stats.stats1.tp_packets++;
 	if (copy_skb) {
 		status |= TP_STATUS_COPY;
+		skb_clear_delivery_time(copy_skb);
 		__skb_queue_tail(&sk->sk_receive_queue, copy_skb);
 	}
 	spin_unlock(&sk->sk_receive_queue.lock);