Re: [PATCH net] igb: only strip Rx timestamp header on the first buffer of a frame
From: Tony Nguyen
Date: Thu Jun 18 2026 - 13:38:42 EST
On 6/15/2026 12:43 AM, Kurt Kanzenbach wrote:
Hi,Hi Tjerk,
On Fri Jun 12 2026, Tjerk Kusters wrote:
Hi,
The patch is attached (0001-igb-only-strip-Rx-timestamp-header-on-the-first-buff.patch)
as my mail setup cannot send it inline via git send-email; apologies for the
attachment.
b4 has a web submission endpoint. Maybe you can use that one:
https://b4.docs.kernel.org/en/latest/contributor/send.html
It would be great if you could get this setup as it makes patch handling easier.
[snip]
From fee3e3452dfcd7e109332369672a3e0090cadeb3 Mon Sep 17 00:00:00 2001
From: T Kusters <tkusters@xxxxxxxx>
Date: Tue, 9 Jun 2026 14:06:24 +0200
Subject: [PATCH net] igb: only strip Rx timestamp header on the first buffer
of a frame
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, ×tamp);
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
Signed-off-by: T Kusters <tkusters@xxxxxxxx>
Sign off should be your full name.
Thanks,
Tony
Great explanation! igb_clean_rx_irq_zc() does not need the same
treatment, correct?
Reviewed-by: Kurt Kanzenbach <kurt@xxxxxxxxxxxxx>
---
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 */
- 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,
--
2.27.0