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Date: Thu, 24 Sep 2026 10:18:08 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Eric Dumazet <edumazet@google.com>, Willem de Bruijn
 <willemdebruijn.kernel@gmail.com>, Paulos Yibelo <habte.yibelo@gmail.com>,
 netdev@vger.kernel.org, richard@nod.at, anton.ivanov@cambridgegreys.com,
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 virtualization@lists.linux.dev, netfilter-devel@vger.kernel.org,
 coreteam@netfilter.org, bridge@lists.linux.dev,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH net v6 1/2] net: validate virtio checksum start after
 network header
Message-ID: <20260924101808.638f2d22@kernel.org>
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On Wed, 23 Sep 2026 22:02:57 -0400 Michael S. Tsirkin wrote:
> $ git grep 'skb->csum_start\ ='
> drivers/net/ethernet/hisilicon/hns3/hns3_enet.c:        skb->csum_start = (unsigned char *)th - skb->head;
> drivers/net/ethernet/mellanox/mlx5/core/en_rx.c:        skb->csum_start = (unsigned char *)uh - skb->head;
> drivers/net/ethernet/mellanox/mlx5/core/en_rx.c:        skb->csum_start = (unsigned char *)uh - skb->head;
> drivers/net/ethernet/mellanox/mlx5/core/en_rx.c:        skb->csum_start = (unsigned char *)tcp - skb->head;
> drivers/net/ethernet/mellanox/mlx5/core/en_rx.c:        skb->csum_start = (unsigned char *)tcp - skb->head;

These are HW-GRO, ASIC coalesced TCP segments so it better know 
the _correct_ offsets of things. And it's hardly remote-provided?

> drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c:         skb->csum_start = skb_transport_header(skb) - skb->head;

selftest