From: Jesper Dangaard Brouer Date: Mon, 3 Mar 2014 13:45:39 +0000 (+0100) Subject: netfilter: avoid race with exp->master ct X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=e1b207dac13ddb2f8ddebc7dc9729a97421909bd;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git 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 Signed-off-by: Florian Westphal Signed-off-by: David S. Miller Signed-off-by: Pablo Neira Ayuso --- 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); 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; }