linux-kernel - Re: [PATCH 5.2 14/66] net_sched: unset TCQ_F_CAN

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Date:   Sun, 28 Jul 2019 08:21:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 5.2 14/66] net_sched: unset TCQ_F_CAN_BYPASS when adding
 filters

On Sat, Jul 27, 2019 at 05:24:20PM -0400, Sasha Levin wrote:
> On Fri, Jul 26, 2019 at 05:24:13PM +0200, Greg Kroah-Hartman wrote:
> > From: Cong Wang <xiyou.wangcong@...il.com>
> > 
> > [ Upstream commit 3f05e6886a595c9a29a309c52f45326be917823c ]
> > 
> > For qdisc's that support TC filters and set TCQ_F_CAN_BYPASS,
> > notably fq_codel, it makes no sense to let packets bypass the TC
> > filters we setup in any scenario, otherwise our packets steering
> > policy could not be enforced.
> > 
> > This can be reproduced easily with the following script:
> > 
> > ip li add dev dummy0 type dummy
> > ifconfig dummy0 up
> > tc qd add dev dummy0 root fq_codel
> > tc filter add dev dummy0 parent 8001: protocol arp basic action mirred egress redirect dev lo
> > tc filter add dev dummy0 parent 8001: protocol ip basic action mirred egress redirect dev lo
> > ping -I dummy0 192.168.112.1
> > 
> > Without this patch, packets are sent directly to dummy0 without
> > hitting any of the filters. With this patch, packets are redirected
> > to loopback as expected.
> > 
> > This fix is not perfect, it only unsets the flag but does not set it back
> > because we have to save the information somewhere in the qdisc if we
> > really want that. Note, both fq_codel and sfq clear this flag in their
> > ->bind_tcf() but this is clearly not sufficient when we don't use any
> > class ID.
> > 
> > Fixes: 23624935e0c4 ("net_sched: TCQ_F_CAN_BYPASS generalization")
> > Cc: Eric Dumazet <edumazet@...gle.com>
> > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> > Reviewed-by: Eric Dumazet <edumazet@...gle.com>
> > Signed-off-by: David S. Miller <davem@...emloft.net>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> There's a fix for this one:
> 
> 	503d81d428bd5 ("net: sched: verify that q!=NULL before setting
> 	q->flags").

Thanks for this, now queued up.

greg k-h