netdev - Re: [PATCH net] ipv4: Fix incorrect source address in Record Route option

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Message-ID: <ZpkugkU/HQ4QUPfU@debian>
Date: Thu, 18 Jul 2024 17:02:26 +0200
From: Guillaume Nault <gnault@...hat.com>
To: Ido Schimmel <idosch@...dia.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
	pabeni@...hat.com, edumazet@...gle.com, dsahern@...nel.org
Subject: Re: [PATCH net] ipv4: Fix incorrect source address in Record Route
 option

On Thu, Jul 18, 2024 at 03:34:07PM +0300, Ido Schimmel wrote:
> The Record Route IP option records the addresses of the routers that
> routed the packet. In the case of forwarded packets, the kernel performs
> a route lookup via fib_lookup() and fills in the preferred source
> address of the matched route.
> 
> The lookup is performed with the DS field of the forwarded packet, but
> using the RT_TOS() macro which only masks one of the two ECN bits. If
> the packet is ECT(0) or CE, the matched route might be different than
> the route via which the packet was forwarded as the input path masks
> both of the ECN bits, resulting in the wrong address being filled in the
> Record Route option.
> 
> Fix by masking both of the ECN bits.

Reviewed-by: Guillaume Nault <gnault@...hat.com>