Date: Tue, 17 Apr 2012 10:06:15 +0200 From: =?ISO-8859-1?Q?Ermal_Lu=E7i?= <eri@freebsd.org> To: Gleb Smirnoff <glebius@freebsd.org> Cc: freebsd-pf@freebsd.org Subject: Re: kern/164402: [pf] pf crashes with a particular set of rules when first matching packet arrives Message-ID: <CAPBZQG2Tjg36GNCBetRZ20FhQnL1sK9i_-oQDDb97bcb4N=sLA@mail.gmail.com> In-Reply-To: <20120416185949.GC92286@FreeBSD.org> References: <201204151200.q3FC0LT5085161@freefall.freebsd.org> <20120416185949.GC92286@FreeBSD.org>
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2012/4/16 Gleb Smirnoff <glebius@freebsd.org>:
> On Sun, Apr 15, 2012 at 12:00:21PM +0000, Gleb Smirnoff wrote:
> T> On Sun, Apr 15, 2012 at 11:10:03AM +0000, Gleb Smirnoff wrote:
> T> T> I have a vague suspicion on what is happening. Your description of
> T> T> the problem looks like if a packet processing in the kernel has entered
> T> T> an endless loop.
> T> T>
> T> T> Looking at pf_route() I see such possibility. From OpenBSD we have
> T> T> this protection against endless looping:
> T> T>
> T> T> if ((*m)->m_pkthdr.pf.routed++ > 3) {
> T> T> m0 = *m;
> T> T> *m = NULL;
> T> T> goto bad;
> T> T> }
> T> T>
> T> T> In our code this transforms to:
> T> T>
> T> T> if (pd->pf_mtag->routed++ > 3) {
> T> T> m0 = *m;
> T> T> *m = NULL;
> T> T> goto bad;
> T> T> }
> T> T>
> T> T> The root difference between storing the tag on mbuf and on pfdesc
> T> T> is that we lose pfdesc, and thus the tag, when we enter pf_test()
> T> T> recursively. And pf_route() does this recursion:
> T> T>
> T> T> if (oifp != ifp) {
> T> T> if (pf_test(PF_OUT, ifp, &m0, NULL) != PF_PASS) {
> T> T> goto bad;
> T> T> ....
> T>
> T> On second look I see that my suspicion may not be true. In the
> T> beginning of pf_test() we do pf_get_mtag() which preserves already
> T> present tag if there is one.
>
> Further investigation showed that problem exist when route applied
> ends in lo0, and packet passes to if_simloop(). There all mtags are
> stripped from the mbuf, including the pf mtag. Then packet is again
> processed by ip_input() again entering pf(4), if it again matches
> a routing rule, then we got an endless loop.
>
> We can try to fix this applying MTAG_PERSISTENT to the pf(4) tag id.
>
That seems like the best fix for this case.
> --
> Totus tuus, Glebius.
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--
Ermal
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