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Date: Sun, 15 Apr 2012 15:51:24 +0400
From: Gleb Smirnoff <glebius@FreeBSD.org>
To: freebsd-pf@FreeBSD.org
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User-Agent: Mutt/1.5.21 (2010-09-15)
Cc: bug-followup@FreeBSD.org
Subject: Re: kern/164402: [pf] pf crashes with a particular set of rules when
 first matching packet arrives
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On Sun, Apr 15, 2012 at 11:10:03AM +0000, Gleb Smirnoff wrote:
T>    I have a vague suspicion on what is happening. Your description of
T>  the problem looks like if a packet processing in the kernel has entered
T>  an endless loop.
T>  
T>    Looking at pf_route() I see such possibility. From OpenBSD we have
T>  this protection against endless looping:
T>  
T>          if ((*m)->m_pkthdr.pf.routed++ > 3) {
T>                  m0 = *m;
T>                  *m = NULL;
T>                  goto bad;
T>          }
T>  
T>  In our code this transforms to:
T>  
T>          if (pd->pf_mtag->routed++ > 3) {
T>                  m0 = *m;
T>                  *m = NULL;
T>                  goto bad;
T>          }
T>  
T>  The root difference between storing the tag on mbuf and on pfdesc
T>  is that we lose pfdesc, and thus the tag, when we enter pf_test()
T>  recursively. And pf_route() does this recursion:
T>  
T>          if (oifp != ifp) {
T>                  if (pf_test(PF_OUT, ifp, &m0, NULL) != PF_PASS) {
T>                          goto bad;
T>  	....

On second look I see that my suspicion may not be true. In the
beginning of pf_test() we do pf_get_mtag() which preserves already
present tag if there is one.

-- 
Totus tuus, Glebius.