[PATCH net] wireguard: queueing: preserve tstamp_type in wg_reset_packet()

[PATCH net] wireguard: queueing: preserve tstamp_type in wg_reset_packet()

[Ramses de Norre via B4 Relay]

From: Ramses de Norre <ramses@well-founded.dev>

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 <ramses@well-founded.dev>
---
 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 79b6d70de236b..663b19b783953 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;

---
base-commit: 24ef02f934eeb48830cff6b739abc3c62b1d107b
change-id: 20260817-wg-tstamp-b327825122dc

Best regards,
--  
Ramses de Norre <ramses@well-founded.dev>

Re: [PATCH net] wireguard: queueing: preserve tstamp_type in wg_reset_packet()

[Toke Høiland-Jørgensen]

Ramses de Norre via B4 Relay
<devnull+ramses.well-founded.dev@kernel.org> writes:

> From: Ramses de Norre <ramses@well-founded.dev>
>
> 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 <ramses@well-founded.dev>

Seems reasonable:

Reviewed-by: Toke Høiland-Jørgensen <toke@kernel.org>

Re: [PATCH net] wireguard: queueing: preserve tstamp_type in wg_reset_packet()

[Eric Dumazet]

On Thu, Aug 27, 2026 at 3:28 PM Toke Høiland-Jørgensen <toke@kernel.org> wrote:
>
> Ramses de Norre via B4 Relay
> <devnull+ramses.well-founded.dev@kernel.org> writes:
>
> > From: Ramses de Norre <ramses@well-founded.dev>
> >
> > 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 <ramses@well-founded.dev>
>
> Seems reasonable:
>
> Reviewed-by: Toke Høiland-Jørgensen <toke@kernel.org>

Reviewed-by: Eric Dumazet <edumazet@google.com>

Thanks.

Re: [PATCH net] wireguard: queueing: preserve tstamp_type in wg_reset_packet()

[Jason A. Donenfeld]

On Thu, Aug 27, 2026 at 01:52:56PM +0200, Ramses de Norre via B4 Relay wrote:
> From: Ramses de Norre <ramses@well-founded.dev>
> 
> 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 <ramses@well-founded.dev>
> ---
>  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 79b6d70de236b..663b19b783953 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;

Seems reasonable to me. I'll put this through the paces testing and
queue it up when I'm back at my laptop on Monday.

Jason