linux-kernel - Re: [PATCH net] net: tcp: Update the type of scaling

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Date: Mon, 6 May 2024 14:35:01 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Horatiu Vultur <horatiu.vultur@...rochip.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, soheil@...gle.com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: tcp: Update the type of scaling_ratio

On Mon, May 6, 2024 at 2:04 PM Horatiu Vultur
<horatiu.vultur@...rochip.com> wrote:
>
> It was noticed the following issue that sometimes the scaling_ratio was
> getting a value of 0, meaning that window space was having a value of 0,
> so then the tcp connection was stopping.
> The reason why the scaling_ratio was getting a value of 0 is because
> when it was calculated, it was truncated from a u64 to a u8. So for
> example if it scaling_ratio was supposed to be 256 it was getting a
> value of 0.
> The fix consists in chaning the type of scaling_ratio from u8 to u16.
>
> Fixes: dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale")
> Signed-off-by: Horatiu Vultur <horatiu.vultur@...rochip.com>
> ---

This is a wrong patch. We need to fix the root cause instead.

By definition, skb->len / skb->truesize must be < 1

If not, a driver is lying to us and this is quite bad.

Please take a look at the following patch for a real fix.

4ce62d5b2f7aecd4900e7d6115588ad7f9acccca net: usb: ax88179_178a: stop
lying about skb->truesize