netdev - Re: [PATCH net] bridge: Fix incorrect re-injection of STP packets

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Message-ID: <20160605074004.GA4491@colbert.mtl.com>
Date:	Sun, 5 Jun 2016 10:40:04 +0300
From:	Ido Schimmel <idosch@...lanox.com>
To:	<stephen@...workplumber.org>, <davem@...emloft.net>, <fw@...len.de>
CC:	<bridge@...ts.linux-foundation.org>, <netdev@...r.kernel.org>,
	<eladr@...lanox.com>, <ogerlitz@...lanox.com>, <jiri@...lanox.com>,
	<yotamg@...lanox.com>, <nogahf@...lanox.com>
Subject: Re: [PATCH net] bridge: Fix incorrect re-injection of STP packets

Hi Florian,

Fri, Jun 03, 2016 at 12:39:45PM IDT, idosch@...lanox.com wrote:
>Commit 8626c56c8279 ("bridge: fix potential use-after-free when hook
>returns QUEUE or STOLEN verdict") fixed incorrect usage of NF_HOOK's
>return value by consuming packets in okfn via br_pass_frame_up().
>
>However, this function re-injects packets to the Rx path with skb->dev
>set to the bridge device, which breaks kernel's STP, as all STP packets
>appear to originate from the bridge device itself.
>
>Instead, if okfn was called for a packet, make bridge's rx_handler
>re-inject it to the Rx path by returning RX_HANDLER_PASS. This is
>consistent with previous behavior.
>
>Cc: Florian Westphal <fw@...len.de>
>Fixes: 8626c56c8279 ("bridge: fix potential use-after-free when hook returns QUEUE or STOLEN verdict")
>Reviewed-by: Jiri Pirko <jiri@...lanox.com>
>Signed-off-by: Ido Schimmel <idosch@...lanox.com>

I read your commit more closely and also looked at nf_reinject() and I'm
not sure how the fix should be carried out.

After packet is processed by okfn it should return to the Rx path -
by making bridge's rx_handler return RX_HANDLER_PASS - so that it 
could be picked up by the packet handlers.

However, if verdict is NF_QUEUE and packet is later re-injected via
nf_reinject() then this can't happen, as rx_handler already returned
RX_HANDLER_CONSUMED for the packet.

So, my patch is wrong because it doesn't consume the packet in okfn, but
yours consumes it in a way which breaks current packet handlers.

Any suggestions regarding a fix? I have a feeling I'm missing something
obvious.

Thanks!