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Date: Sun, 15 Apr 2012 12:00:21 GMT
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To: freebsd-pf@FreeBSD.org
From: Gleb Smirnoff <glebius@FreeBSD.org>
Cc: 
Subject: Re: kern/164402: [pf] pf crashes with a particular set of rules when
 first matching packet arrives
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The following reply was made to PR kern/164402; it has been noted by GNATS.

From: Gleb Smirnoff <glebius@FreeBSD.org>
To: freebsd-pf@FreeBSD.org
Cc: bug-followup@FreeBSD.org
Subject: Re: kern/164402: [pf] pf crashes with a particular set of rules when
 first matching packet arrives
Date: Sun, 15 Apr 2012 15:51:24 +0400

 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.