netfilter: avoid race with exp->master ct

Preparation for disconnecting the nf_conntrack_lock from the
expectations code.  Once the nf_conntrack_lock is lifted, a race
condition is exposed.

The expectations master conntrack exp->master, can race with
delete operations, as the refcnt increment happens too late in
init_conntrack().  Race is against other CPUs invoking
->destroy() (destroy_conntrack()), or nf_ct_delete() (via timeout
or early_drop()).

Avoid this race in nf_ct_find_expectation() by using atomic_inc_not_zero(),
and checking if nf_ct_is_dying() (path via nf_ct_delete()).

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 289b27901d8c..92d597788d6a 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -902,6 +902,7 @@ init_conntrack(struct net *net, struct nf_conn *tmpl,
 			 ct, exp);
 		/* Welcome, Mr. Bond.  We've been expecting you... */
 		__set_bit(IPS_EXPECTED_BIT, &ct->status);
+		/* exp->master safe, refcnt bumped in nf_ct_find_expectation */
 		ct->master = exp->master;
 		if (exp->helper) {
 			help = nf_ct_helper_ext_add(ct, exp->helper,
@@ -916,7 +917,6 @@ init_conntrack(struct net *net, struct nf_conn *tmpl,
 #ifdef CONFIG_NF_CONNTRACK_SECMARK
 		ct->secmark = exp->master->secmark;
 #endif
-		nf_conntrack_get(&ct->master->ct_general);
 		NF_CT_STAT_INC(net, expect_new);
 	} else {
 		__nf_ct_try_assign_helper(ct, tmpl, GFP_ATOMIC);