netdev - Re: Question about an assignment in handle

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Date:	Sun, 30 May 2010 09:29:10 -0400
From:	jamal <hadi@...erus.ca>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Jiri Pirko <jpirko@...hat.com>, netdev@...r.kernel.org,
	davem@...emloft.net, kaber@...sh.net
Subject: Re: Question about an assignment in handle_ing()

On Wed, 2010-05-26 at 07:38 -0400, jamal wrote:
> On Wed, 2010-05-26 at 09:13 +1000, Herbert Xu wrote:
> 
> > If it did happen like you said then it would be a serious bug
> > in our stack as everything else (including the TCP stack) relies
> > on this.
> 
> It could have been a bug. Note this was not a simple test, so there
> may be other factors involved. If you or Jiri are willing to run the
> test i will construct a scenario which will test this out. It will need
> a compile of the kernel and a small check in pedit to see if we see
> cloned skbs when we run the two tcpdumps (and to make sure the tcpdumps
> see the correct bytes). Otherwise i will get to it by weekend.

I have constructed a test case (attached) and my fear is unfortunately
still there;-< What am i doing wrong?

The packet path is:
-->eth0-->tcpdump eth0-->pedit-->mirror to dummy0-->tcpdump dummy0

I expect pedit to see a cloned packet. It doesnt. The check is in
tcf_pedit(), just before "if (!(skb->tc_verd & TC_OK2MUNGE))"
added: 
printk("pedit: skb-%p is %s\n",skb,skb_cloned(skb)?"cloned":"!cloned");

Is pf packet not cloning etc? Sorry, I dont have much time today
to dig into the code - but i figure youd know the answer.

> > But how can the caller make that decision when you return exactly
> > the same value in the error case as the normal case?
> 
> Ok - i see your point Herbert ;-> 
> it makes sense to have pedit have an error action code like some of the
> others actions which defaults to a drop.
> I will do a proper patch sometime this weekend.

I will get it done this week.

cheers,
jamal

View attachment "jiri-q-test" of type "text/plain" (1856 bytes)