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

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Eric Dumazet <edumazet@google.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@google.com>

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

Thanks,
Olek