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Date: Thu, 1 Aug 2024 16:06:33 +0200
From: Florian Westphal <fw@strlen.de>
To: Moon Yeounsu <yyyynoom@gmail.com>
Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
	pabeni@redhat.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, intel-wired-lan@lists.osuosl.org
Subject: Re: [PATCH] e1000e: use ip_hdrlen() instead of bit shift
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Moon Yeounsu <yyyynoom@gmail.com> wrote:
> There's no reason to use bit shift to find the UDP header.
> It's not intuitive and it reinvents well-defined functions.
> 
> Signed-off-by: Moon Yeounsu <yyyynoom@gmail.com>
> ---
>  drivers/net/ethernet/intel/e1000e/netdev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
> index 360ee26557f7..07c4cf84bdf3 100644
> --- a/drivers/net/ethernet/intel/e1000e/netdev.c
> +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
> @@ -5731,7 +5731,7 @@ static int e1000_transfer_dhcp_info(struct e1000_adapter *adapter,
>  		if (ip->protocol != IPPROTO_UDP)
>  			return 0;
>  
> -		udp = (struct udphdr *)((u8 *)ip + (ip->ihl << 2));
> +		udp = (struct udphdr *)((u8 *)ip + ip_hdrlen(skb));

This helper needs skb_network_header being set up correctly, are you
sure thats the case here?  ip pointer is fetched via data + 14 right
above, so it doesn't look like this would work.