[nf-next PATCH V2 3/5] netfilter: avoid race with exp->master ct
From: Jesper Dangaard Brouer <hidden>
Date: 2014-02-28 12:17:24
Also in:
netfilter-devel
Subsystem:
netfilter, networking [general], the rest · Maintainers:
Pablo Neira Ayuso, Florian Westphal, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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 <redacted> Signed-off-by: Florian Westphal <fw@strlen.de> --- V2: Address Florian Westphal concerns * add check after !nf_ct_is_confirmed() * handle exit case if del_timer(&exp->timeout) fails net/netfilter/nf_conntrack_core.c | 2 +- net/netfilter/nf_conntrack_expect.c | 14 ++++++++++++++ 2 files changed, 15 insertions(+), 1 deletions(-)
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 289b279..92d5977 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);
diff --git a/net/netfilter/nf_conntrack_expect.c b/net/netfilter/nf_conntrack_expect.c
index 4fd1ca9..1867bad 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; }