RE: [Intel-wired-lan] [PATCH net v2] igb: only strip Rx timestamp header on the first buffer of a frame

[Kwapulinski, Piotr]

>-----Original Message-----
>From: Intel-wired-lan <intel-wired-lan-bounces@xxxxxxxxxx> On Behalf Of Tjerk Kusters via B4 Relay
>Sent: Friday, June 19, 2026 9:15 AM
>To: Nguyen, Anthony L <anthony.l.nguyen@xxxxxxxxx>; Kitszel, Przemyslaw <przemyslaw.kitszel@xxxxxxxxx>; Andrew Lunn <andrew+netdev@xxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>; Eric Dumazet <edumazet@xxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>; Richard Cochran <richardcochran@xxxxxxxxx>; Jesper Dangaard Brouer <hawk@xxxxxxxxxx>; Kurt Kanzenbach <kurt@xxxxxxxxxxxxx>
>Cc: intel-wired-lan@xxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx; Tjerk Kusters <tkusters@xxxxxxxx>
>Subject: [Intel-wired-lan] [PATCH net v2] igb: only strip Rx timestamp header on the first buffer of a frame
>
>From: Tjerk Kusters <tkusters@xxxxxxxx>
>
>When Rx hardware timestamping is enabled (e.g. ptp4l, which configures HWTSTAMP_FILTER_ALL), the NIC prepends a 16-byte timestamp header to the first Rx buffer of every received frame. igb_clean_rx_irq() strips this header inside its per-buffer loop:
>
>	if (igb_test_staterr(rx_desc, E1000_RXDADV_STAT_TSIP)) {
>		ts_hdr_len = igb_ptp_rx_pktstamp(rx_ring->q_vector,
>						 pktbuf, &timestamp);
>		pkt_offset += ts_hdr_len;
>		size -= ts_hdr_len;
>	}
>
>For a frame that spans more than one Rx buffer (e.g. a jumbo frame), this block runs once per buffer. The timestamp header only exists at the start of the first buffer, but igb_ptp_rx_pktstamp() is called for every buffer.
>
>On a continuation buffer the data is packet payload, not a timestamp header. igb_ptp_rx_pktstamp() already has two guards against acting on a non-header buffer: it returns 0 if PTP is disabled, and returns 0 if the reserved dwords (the first 8 bytes) are non-zero. Neither is sufficient
>here: PTP is enabled, and a continuation buffer whose payload happens to begin with 8 zero bytes passes the reserved-dword check. In that case the payload is mistaken for a valid timestamp header and igb_ptp_rx_pktstamp() returns IGB_TS_HDR_LEN, so the caller strips 16 bytes of real data from that buffer. A frame spanning N buffers whose continuation buffers start with zero bytes therefore loses 16 * (N - 1) bytes from its tail.
>
>This is easily triggered by a GigE Vision camera streaming dark frames (mostly 0x00 pixel data) over jumbo UDP with PTP active on the receiver:
>the all-zero frames arrive truncated while frames with non-zero content are fine. There is no error indication.
>
>No content-based check can reliably tell a continuation buffer that begins with zero bytes from a real timestamp header, because both are all zero.
>Fix it structurally instead: only attempt the strip on the first buffer of a frame, which is the only buffer that can contain a timestamp header. In
>igb_clean_rx_irq() skb is NULL until the first buffer has been processed, so guarding the strip with !skb restricts it to the first buffer regardless of payload content.
>
>Fixes: 5379260852b0 ("igb: Fix XDP with PTP enabled")
>Cc: stable@xxxxxxxxxxxxxxx
>Reviewed-by: Kurt Kanzenbach <kurt@xxxxxxxxxxxxx>
>Signed-off-by: Tjerk Kusters <tkusters@xxxxxxxx>
>---
>Changes in v2:
> - resend via b4 (v1 was sent with a mail client)
> - use full author name "Tjerk Kusters" (Jacob Keller)
> - add Reviewed-by from Kurt Kanzenbach
> - no functional change
>
>Link to v1: https://lore.kernel.org/all/PAWPR05MB1069106D52F4E17F1EDB99C67B9182@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>---
> drivers/net/ethernet/intel/igb/igb_main.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
>index ce91dda00ec0..abb55cd589a9 100644
>--- a/drivers/net/ethernet/intel/igb/igb_main.c
>+++ b/drivers/net/ethernet/intel/igb/igb_main.c
>@@ -9061,7 +9061,8 @@ static int igb_clean_rx_irq(struct igb_q_vector *q_vector, const int budget)
> 		pktbuf = page_address(rx_buffer->page) + rx_buffer->page_offset;
> 
> 		/* pull rx packet timestamp if available and valid */
Is this comment up-to-date now ?
Reviewed-by: Piotr Kwapulinski <piotr.kwapulinski@xxxxxxxxx>

>-		if (igb_test_staterr(rx_desc, E1000_RXDADV_STAT_TSIP)) {
>+		if (!skb &&
>+		    igb_test_staterr(rx_desc, E1000_RXDADV_STAT_TSIP)) {
> 			int ts_hdr_len;
> 
> 			ts_hdr_len = igb_ptp_rx_pktstamp(rx_ring->q_vector,
>
>---
>base-commit: 2d3090a8aeb596a26935db0955d46c9a5db5c6ce
>change-id: 20260619-igb-rx-ts-fix-cd70585ee316
>
>Best regards,
>--
>Tjerk Kusters <tkusters@xxxxxxxx>
>
>