From 35d6223b91189e87c3b6d2edb8e493a739ad2f29 Mon Sep 17 00:00:00 2001 From: Ramses de Norre Date: Thu, 27 Aug 2026 13:52:56 +0200 Subject: wireguard: queueing: preserve tstamp_type when encapsulating packet MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sending traffic through a wireguard tunnel on a host using the fq qdisc fills the log with: fq: likely mono tstamp with tstamp_type 0 An skb carries a timestamp in skb->tstamp and, separately, a skb->tstamp_type field recording which clock that timestamp came from. The two have to agree. When wireguard encapsulates a packet it calls wg_reset_packet(), which clears the fields that must not leak from the inner packet into the tunnel packet. It does so in two steps: skb_scrub_packet(skb, true); memset(&skb->headers, 0, sizeof(skb->headers)); skb_scrub_packet() deliberately keeps skb->tstamp when it holds a monotonic timestamp: that value is the time the packet is scheduled to be sent, and the qdisc still needs it. The memset then zeroes skb->tstamp_type, because that field sits inside the headers group while skb->tstamp does not. The packet therefore leaves wireguard carrying a monotonic timestamp labelled as a realtime one. Nothing noticed until commit c4f796c4f16b ("net_sched: sch_fq: convert skb->tstamp if not monotonic"): fq used to assume every timestamp was monotonic. It now consults tstamp_type, spots the mismatch, warns, and falls back to treating the value as monotonic. Pacing still ends up correct, so the log spam is the actual problem. Save tstamp_type before the memset and restore it when encapsulating, next to the hash fields that are already carried over this way. When decapsulating it stays zeroed, which is right: an incoming packet's timestamp is a realtime receive timestamp. Fixes: de799101519a ("net: Add skb_clear_tstamp() to keep the mono delivery_time") Signed-off-by: Ramses de Norre Reviewed-by: Toke Høiland-Jørgensen Reviewed-by: Eric Dumazet Cc: stable@vger.kernel.org Signed-off-by: Jason A. Donenfeld --- drivers/net/wireguard/queueing.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/net/wireguard/queueing.h b/drivers/net/wireguard/queueing.h index 79b6d70de236..663b19b78395 100644 --- a/drivers/net/wireguard/queueing.h +++ b/drivers/net/wireguard/queueing.h @@ -78,12 +78,14 @@ static inline void wg_reset_packet(struct sk_buff *skb, bool encapsulating) u8 l4_hash = skb->l4_hash; u8 sw_hash = skb->sw_hash; u32 hash = skb->hash; + u8 tstamp_type = skb->tstamp_type; skb_scrub_packet(skb, true); memset(&skb->headers, 0, sizeof(skb->headers)); if (encapsulating) { skb->l4_hash = l4_hash; skb->sw_hash = sw_hash; skb->hash = hash; + skb->tstamp_type = tstamp_type; } skb->queue_mapping = 0; skb->nohdr = 0; -- cgit v1.3-14-g43fede