netdev - Re: [PATCH ipsec,v2] xfrm: fix "disable_policy" flag use when arriving from different devices

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Date:   Wed, 18 May 2022 10:11:59 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Eyal Birger <eyal.birger@...il.com>
CC:     <davem@...emloft.net>, <yoshfuji@...ux-ipv6.org>,
        <dsahern@...nel.org>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <herbert@...dor.apana.org.au>,
        <nicolas.dichtel@...nd.com>, <netdev@...r.kernel.org>,
        Shmulik Ladkani <shmulik.ladkani@...il.com>
Subject: Re: [PATCH ipsec,v2] xfrm: fix "disable_policy" flag use when
 arriving from different devices

On Fri, May 13, 2022 at 11:34:02PM +0300, Eyal Birger wrote:
> In IPv4 setting the "disable_policy" flag on a device means no policy
> should be enforced for traffic originating from the device. This was
> implemented by seting the DST_NOPOLICY flag in the dst based on the
> originating device.
> 
> However, dsts are cached in nexthops regardless of the originating
> devices, in which case, the DST_NOPOLICY flag value may be incorrect.
> 
> Consider the following setup:
> 
>                      +------------------------------+
>                      | ROUTER                       |
>   +-------------+    | +-----------------+          |
>   | ipsec src   |----|-|ipsec0           |          |
>   +-------------+    | |disable_policy=0 |   +----+ |
>                      | +-----------------+   |eth1|-|-----
>   +-------------+    | +-----------------+   +----+ |
>   | noipsec src |----|-|eth0             |          |
>   +-------------+    | |disable_policy=1 |          |
>                      | +-----------------+          |
>                      +------------------------------+
> 
> Where ROUTER has a default route towards eth1.
> 
> dst entries for traffic arriving from eth0 would have DST_NOPOLICY
> and would be cached and therefore can be reused by traffic originating
> from ipsec0, skipping policy check.
> 
> Fix by setting a IPSKB_NOPOLICY flag in IPCB and observing it instead
> of the DST in IN/FWD IPv4 policy checks.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: Shmulik Ladkani <shmulik.ladkani@...il.com>
> Signed-off-by: Eyal Birger <eyal.birger@...il.com>
> 
> ---
> 
> v2: set IPSKB_NOPOLICY in ip_route_input_mc() as needed

Applied, thanks a lot Eyal!