From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: netdev@vger.kernel.org, jamal <hadi@cyberus.ca>
Subject: Re: act_mirred: Fix bogus header when redirecting from VLAN
Date: Thu, 16 Apr 2015 19:40:30 -0700 [thread overview]
Message-ID: <20150417024029.GA6718@Alexeis-MacBook-Pro.local> (raw)
In-Reply-To: <20150417021501.GB22835@gondor.apana.org.au>
On Fri, Apr 17, 2015 at 10:15:01AM +0800, Herbert Xu wrote:
> > seems the cleaner fix will be to push skb->mac_len instead?
>
> No skb->mac_len is the same as skb2->dev->hard_header_len.
hmm. please help me understand the problem then.
In the commit log you mentioned that your vlan dev and ifb
have unequal hard header length. I think that can only happen if
your master dev used to create vlan, didn't have vlan offload,
so vlandev->hhl = 18 and ifb->hhl = 14. Then when tagged packet
arrives on master device we call skb_vlan_untag() and
skb->mac_len becomes 14, then vlan_do_receive() will do
another_round, ingress qdisc will trigger and act_mirred
eventually will be called. So existing act_mirred will be pushing
18 bytes, whereas only 14 bytes are valid and the lowest 4 have junk.
By 'fixing it' using ifb's 14 byte the patch is only masking the
problem, no?
next prev parent reply other threads:[~2015-04-17 2:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-17 1:02 act_mirred: Fix bogus header when redirecting from VLAN Herbert Xu
2015-04-17 1:34 ` Alexei Starovoitov
2015-04-17 2:15 ` Herbert Xu
2015-04-17 2:40 ` Alexei Starovoitov [this message]
2015-04-17 5:32 ` [v2] " Herbert Xu
2015-04-17 15:26 ` Alexei Starovoitov
2015-04-17 17:29 ` David Miller
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