[PATCH net] tcp: preserve timestamps across receive queue collapse

When tcp_collapse() rebuilds skbs under memory pressure, the copy
process doesn't include the right tstamp and hwtstamp from the
old skb.

In net timestamping case, if such an skb happens to be the last
one consumed in a recvmsg() call, the application receives no RX
timestamp for that call.

Fix this by copying both tstamp and hwtstamp to the new skb right
after the initialization.

Fixes: 98aaa913b4ed ("tcp: Extend SOF_TIMESTAMPING_RX_SOFTWARE to TCP recvmsg")
Signed-off-by: Jason Xing <redacted>
---
 net/ipv4/tcp_input.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0f60a1dbf927..c5756db892f2 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c

@@ -5835,6 +5835,8 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
 
 		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
 		skb_copy_decrypted(nskb, skb);
+		nskb->tstamp = skb->tstamp;
+		skb_hwtstamps(nskb)->hwtstamp = skb_hwtstamps(skb)->hwtstamp;
 		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
 		if (list)
 			__skb_queue_before(list, skb, nskb);

-- 
2.43.5