netdev - Re: [PATCH v4 net-next 09/14] gro: prevent ACE field corruption & better AccECN handling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <eb04ddfd-6e17-464b-a629-09aed99e2e95@redhat.com>
Date: Tue, 29 Oct 2024 13:03:50 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: chia-yu.chang@...ia-bell-labs.com, netdev@...r.kernel.org,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 dsahern@...nel.org, netfilter-devel@...r.kernel.org, kadlec@...filter.org,
 coreteam@...filter.org, pablo@...filter.org, bpf@...r.kernel.org,
 joel.granados@...nel.org, linux-fsdevel@...r.kernel.org, kees@...nel.org,
 mcgrof@...nel.org, ij@...nel.org, ncardwell@...gle.com,
 koen.de_schepper@...ia-bell-labs.com, g.white@...leLabs.com,
 ingemar.s.johansson@...csson.com, mirja.kuehlewind@...csson.com,
 cheshire@...le.com, rs.ietf@....at, Jason_Livingood@...cast.com,
 vidhi_goel@...le.com
Subject: Re: [PATCH v4 net-next 09/14] gro: prevent ACE field corruption &
 better AccECN handling

On 10/21/24 23:59, chia-yu.chang@...ia-bell-labs.com wrote:
> From: Ilpo Järvinen <ij@...nel.org>
> 
> There are important differences in how the CWR field behaves
> in RFC3168 and AccECN. With AccECN, CWR flag is part of the
> ACE counter and its changes are important so adjust the flags
> changed mask accordingly.
> 
> Also, if CWR is there, set the Accurate ECN GSO flag to avoid
> corrupting CWR flag somewhere.
> 
> Signed-off-by: Ilpo Järvinen <ij@...nel.org>
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> ---
>  net/ipv4/tcp_offload.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index 0b05f30e9e5f..f59762d88c38 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -329,7 +329,7 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb,
>  	th2 = tcp_hdr(p);
>  	flush = (__force int)(flags & TCP_FLAG_CWR);
>  	flush |= (__force int)((flags ^ tcp_flag_word(th2)) &
> -		  ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH));
> +		  ~(TCP_FLAG_FIN | TCP_FLAG_PSH));

If I read correctly, if the peer is using RFC3168 and TSO_ECN, GRO will
now pump into the stack twice the number of packets it was doing prior
to this patch, am I correct?

That is likely causing measurable performance regressions.

>  	flush |= (__force int)(th->ack_seq ^ th2->ack_seq);
>  	for (i = sizeof(*th); i < thlen; i += 4)
>  		flush |= *(u32 *)((u8 *)th + i) ^
> @@ -405,7 +405,7 @@ void tcp_gro_complete(struct sk_buff *skb)
>  	shinfo->gso_segs = NAPI_GRO_CB(skb)->count;
>  
>  	if (th->cwr)
> -		shinfo->gso_type |= SKB_GSO_TCP_ECN;
> +		shinfo->gso_type |= SKB_GSO_TCP_ACCECN;

If this packet is forwarded, it will not leverage TSO anymore - with
current H/W.

I think we need a way to enable this feature conditionally, but I fear
another sysctl will be ugly and the additional conditionals will not be
good for GRO.

Smarter suggestions welcome ;)

Cheers,

Paolo

>  }
>  EXPORT_SYMBOL(tcp_gro_complete);
>