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

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Date:   Thu, 12 May 2022 18:09:40 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Eyal Birger <eyal.birger@...il.com>, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, steffen.klassert@...unet.com,
        herbert@...dor.apana.org.au
Cc:     netdev@...r.kernel.org, Shmulik Ladkani <shmulik.ladkani@...il.com>
Subject: Re: [PATCH ipsec] xfrm: fix "disable_policy" flag use when arriving
 from different devices


Le 12/05/2022 à 12:48, Eyal Birger a écrit :
> 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>
> ---

[snip]

> @@ -1852,8 +1856,7 @@ static int __mkroute_input(struct sk_buff *skb,
>  		}
>  	}
>  
> -	rth = rt_dst_alloc(out_dev->dev, 0, res->type,
> -			   IN_DEV_ORCONF(in_dev, NOPOLICY),
> +	rth = rt_dst_alloc(out_dev->dev, 0, res->type, no_policy,>  			   IN_DEV_ORCONF(out_dev, NOXFRM));
no_policy / DST_NOPOLICY is still needed in the dst entry after this patch?