diff options
author | Jesper Dangaard Brouer <brouer@redhat.com> | 2014-03-03 14:45:39 +0100 |
---|---|---|
committer | Pablo Neira Ayuso <pablo@netfilter.org> | 2014-03-07 11:40:47 +0100 |
commit | e1b207dac13ddb2f8ddebc7dc9729a97421909bd (patch) | |
tree | 971503a1e212f5f42b3e50d9540c9ee409bf30fd /net/netfilter/nf_conntrack_expect.c | |
parent | b7779d06f9950e14a008a2de970b44233fe49c86 (diff) |
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>
Diffstat (limited to 'net/netfilter/nf_conntrack_expect.c')
-rw-r--r-- | net/netfilter/nf_conntrack_expect.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/net/netfilter/nf_conntrack_expect.c b/net/netfilter/nf_conntrack_expect.c index da2f84f41777..f02805e0c7c5 100644 --- a/net/netfilter/nf_conntrack_expect.c +++ b/net/netfilter/nf_conntrack_expect.c @@ -155,6 +155,18 @@ nf_ct_find_expectation(struct net *net, u16 zone, if (!nf_ct_is_confirmed(exp->master)) return NULL; + /* Avoid race with other CPUs, that for exp->master ct, is + * about to invoke ->destroy(), or nf_ct_delete() via timeout + * or early_drop(). + * + * The atomic_inc_not_zero() check tells: If that fails, we + * know that the ct is being destroyed. If it succeeds, we + * can be sure the ct cannot disappear underneath. + */ + if (unlikely(nf_ct_is_dying(exp->master) || + !atomic_inc_not_zero(&exp->master->ct_general.use))) + return NULL; + if (exp->flags & NF_CT_EXPECT_PERMANENT) { atomic_inc(&exp->use); return exp; @@ -162,6 +174,8 @@ nf_ct_find_expectation(struct net *net, u16 zone, nf_ct_unlink_expect(exp); return exp; } + /* Undo exp->master refcnt increase, if del_timer() failed */ + nf_ct_put(exp->master); return NULL; } |