Ani Sinha <ani@xxxxxxxxxx> wrote: > On Sun, Oct 18, 2015 at 2:40 PM, Florian Westphal <fw@xxxxxxxxx> wrote: > > Ani Sinha <ani@xxxxxxxxxx> wrote: > >> Indeed. So it seems to me that we have run into one another such case. > >> In patch c6825c0976fa7893692, I see we have added an additional check (along with comparing tuple and zone) to verify that if the conntrack is confirmed. > >> > >> + return nf_ct_tuple_equal(tuple, &h->tuple) && > >> + nf_ct_zone(ct) == zone && > >> + nf_ct_is_confirmed(ct); > >> > >> This is necessary since it's possible that a conntrack can be recreated with the same zone. > >> Unfortunately, we leave a hole open in __nf_conntrack_confirm() because this routine _is_ responsible > >> for confirming the conntrack. We cannot use the same logic here. > > > > Hmm, why? > > > > I don't understand why we need to change __nf_conntrack_confirm(), can > > you elaborate? > > ok, let's take a step back. The fundamental question I am trying to > find answer to is that whether it is possible for another thread to > deallocate and then reallocate and initialize the conntrack object > while running concurrently during __nf_conntrack_confirm() . Not unless something is broken. > crash), we do not have the patch > > e53376bef2cd97d3e3f61fdc6 > > applied. This patch bumps the refcount before adding the connrack > entry into the unconfirmed list. Yes, that patch fixes such bug. > + /* Now it is inserted into the unconfirmed list, bump refcount */ > + nf_conntrack_get(&ct->ct_general); > > and if we assume the invariant that nf_conntrack_free() is never > called when refcount is !=0, then this would seem to indicate that the > above patch should fix the crash I mentioned in the thread. nf_conntrack_free must only be invoked after refcount becomes zero, right. > One curious piece of hunk is : > > + /* A freed object has refcnt == 0, that's > + * the golden rule for SLAB_DESTROY_BY_RCU > + */ > + NF_CT_ASSERT(atomic_read(&ct->ct_general.use) == 0); > + > First, this assertion only puts a warning log at best when it fails. > Second, if this assertion is false, at some point we will get into a > kernel crash as the one I mentioned. So this assertion effectively > does nothing other than perhaps help in debugging. Right. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
