netdev - Re: [PATCH net] net: gro: clear skb_shinfo(skb)->hwtstamps in napi_reuse

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Message-ID: <e24f9c99-f800-44ed-86a9-8a48739586ab@intel.com>
Date: Wed, 15 Oct 2025 14:04:14 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Eric Dumazet <edumazet@...gle.com>
CC: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>, Willem de Bruijn <willemb@...gle.com>,
	<netdev@...r.kernel.org>, <eric.dumazet@...il.com>
Subject: Re: [PATCH net] net: gro: clear skb_shinfo(skb)->hwtstamps in
 napi_reuse_skb()

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 15 Oct 2025 06:32:21 +0000

> Some network drivers assume this field is zero after napi_get_frags().
> 
> We must clear it in napi_reuse_skb() otherwise the following can happen:
> 
> 1) A packet is received, and skb_shinfo(skb)->hwtstamps is populated
>    because a bit in the receive descriptor announced hwtstamp
>    availability for this packet.
> 
> 2) Packet is given to gro layer via napi_gro_frags().
> 
> 3) Packet is merged to a prior one held in GRO queues.
> 
> 4) skb is saved after some cleanup in napi->skb via a call
>    to napi_reuse_skb().
> 
> 5) Next packet is received 10 seconds later, gets the recycled skb
>    from napi_get_frags().
> 
> 6) The receive descriptor does not announce hwtstamp availability.
>    Driver does not clear shinfo->hwtstamps.
> 
> 7) We have in shinfo->hwtstamps an old timestamp.
> 
> Fixes: ac45f602ee3d ("net: infrastructure for hardware time stamping")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Alexander Lobakin <aleksander.lobakin@...el.com>

Thanks,
Olek