netdev - Re: [PATCH net-next] net/sched: act_mirred: Ensure mac_len is pulled prior redirect to a non mac_header

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Date:   Tue, 24 Dec 2019 07:45:08 -0500
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     shmulik@...anetworks.com, Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>
Cc:     "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        shmulik.ladkani@...il.com,
        Shmulik Ladkani <sladkani@...ofpoint.com>
Subject: Re: [PATCH net-next] net/sched: act_mirred: Ensure mac_len is pulled
 prior redirect to a non mac_header_xmit target device

On 2019-12-23 7:33 a.m., shmulik@...anetworks.com wrote:
> From: Shmulik Ladkani <sladkani@...ofpoint.com>
> 
> There's no skb_pull performed when a mirred action is set at egress of a
> mac device, with a target device/action that expects skb->data to point
> at the network header.
> 
> As a result, either the target device is errornously given an skb with
> data pointing to the mac (egress case), or the net stack receives the
> skb with data pointing to the mac (ingress case).
> 
> E.g:
>   # tc qdisc add dev eth9 root handle 1: prio
>   # tc filter add dev eth9 parent 1: prio 9 protocol ip handle 9 basic \
>     action mirred egress redirect dev tun0
> 
>   (tun0 is a tun device. result: tun0 errornously gets the eth header
>    instead of the iph)
> 

Shmulik - are you able to add a tdc testcase? It will be helpful to
catch future regressions.
I did basic testing i.e have an app reading tun0 from user space
then mirrored(not redirect) packets to tun0 for before and after
patch.

> Revise the push/pull logic of tcf_mirred_act() to not rely on the
> skb_at_tc_ingress() vs tcf_mirred_act_wants_ingress() comparison, as it
> does not cover all "pull" cases.
> 
> Instead, calculate whether the required action on the target device
> requires the data to point at the network header, and compare this to
> whether skb->data points to network header - and make the push/pull
> adjustments as necessary.
> 
> Signed-off-by: Shmulik Ladkani <sladkani@...ofpoint.com>

Tested-by: Jamal Hadi Salim <jhs@...atatu.com>
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal