From c6825c0976fa7893692e0e43b09740b419b23c09 Mon Sep 17 00:00:00 2001 From: Andrey Vagin Date: Wed, 29 Jan 2014 19:34:14 +0100 Subject: [PATCH] netfilter: nf_conntrack: fix RCU race in nf_conntrack_find_get Lets look at destroy_conntrack: hlist_nulls_del_rcu(&ct->tuplehash[IP_CT_DIR_ORIGINAL].hnnode); ... nf_conntrack_free(ct) kmem_cache_free(net->ct.nf_conntrack_cachep, ct); net->ct.nf_conntrack_cachep is created with SLAB_DESTROY_BY_RCU. The hash is protected by rcu, so readers look up conntracks without locks. A conntrack is removed from the hash, but in this moment a few readers still can use the conntrack. Then this conntrack is released and another thread creates conntrack with the same address and the equal tuple. After this a reader starts to validate the conntrack: * It's not dying, because a new conntrack was created * nf_ct_tuple_equal() returns true. But this conntrack is not initialized yet, so it can not be used by two threads concurrently. In this case BUG_ON may be triggered from nf_nat_setup_info(). Florian Westphal suggested to check the confirm bit too. I think it's right. task 1 task 2 task 3 nf_conntrack_find_get ____nf_conntrack_find destroy_conntrack hlist_nulls_del_rcu nf_conntrack_free kmem_cache_free __nf_conntrack_alloc kmem_cache_alloc memset(&ct->tuplehash[IP_CT_DIR_MAX], if (nf_ct_is_dying(ct)) if (!nf_ct_tuple_equal() I'm not sure, that I have ever seen this race condition in a real life. Currently we are investigating a bug, which is reproduced on a few nodes. In our case one conntrack is initialized from a few tasks concurrently, we don't have any other explanation for this. <2>[46267.083061] kernel BUG at net/ipv4/netfilter/nf_nat_core.c:322! ... <4>[46267.083951] RIP: 0010:[] [] nf_nat_setup_info+0x564/0x590 [nf_nat] ... <4>[46267.085549] Call Trace: <4>[46267.085622] [] alloc_null_binding+0x5b/0xa0 [iptable_nat] <4>[46267.085697] [] nf_nat_rule_find+0x5c/0x80 [iptable_nat] <4>[46267.085770] [] nf_nat_fn+0x111/0x260 [iptable_nat] <4>[46267.085843] [] nf_nat_out+0x48/0xd0 [iptable_nat] <4>[46267.085919] [] nf_iterate+0x69/0xb0 <4>[46267.085991] [] ? ip_finish_output+0x0/0x2f0 <4>[46267.086063] [] nf_hook_slow+0x74/0x110 <4>[46267.086133] [] ? ip_finish_output+0x0/0x2f0 <4>[46267.086207] [] ? dst_output+0x0/0x20 <4>[46267.086277] [] ip_output+0xa4/0xc0 <4>[46267.086346] [] raw_sendmsg+0x8b4/0x910 <4>[46267.086419] [] inet_sendmsg+0x4a/0xb0 <4>[46267.086491] [] ? sock_update_classid+0x3a/0x50 <4>[46267.086562] [] sock_sendmsg+0x117/0x140 <4>[46267.086638] [] ? _spin_unlock_bh+0x1b/0x20 <4>[46267.086712] [] ? autoremove_wake_function+0x0/0x40 <4>[46267.086785] [] ? do_ip_setsockopt+0x90/0xd80 <4>[46267.086858] [] ? call_function_interrupt+0xe/0x20 <4>[46267.086936] [] ? ub_slab_ptr+0x20/0x90 <4>[46267.087006] [] ? ub_slab_ptr+0x20/0x90 <4>[46267.087081] [] ? kmem_cache_alloc+0xd8/0x1e0 <4>[46267.087151] [] sys_sendto+0x139/0x190 <4>[46267.087229] [] ? sock_setsockopt+0x16d/0x6f0 <4>[46267.087303] [] ? audit_syscall_entry+0x1d7/0x200 <4>[46267.087378] [] ? __audit_syscall_exit+0x265/0x290 <4>[46267.087454] [] ? compat_sys_setsockopt+0x75/0x210 <4>[46267.087531] [] compat_sys_socketcall+0x13f/0x210 <4>[46267.087607] [] ia32_sysret+0x0/0x5 <4>[46267.087676] Code: 91 20 e2 01 75 29 48 89 de 4c 89 f7 e8 56 fa ff ff 85 c0 0f 84 68 fc ff ff 0f b6 4d c6 41 8b 45 00 e9 4d fb ff ff e8 7c 19 e9 e0 <0f> 0b eb fe f6 05 17 91 20 e2 80 74 ce 80 3d 5f 2e 00 00 00 74 <1>[46267.088023] RIP [] nf_nat_setup_info+0x564/0x590 Cc: Eric Dumazet Cc: Florian Westphal Cc: Pablo Neira Ayuso Cc: Patrick McHardy Cc: Jozsef Kadlecsik Cc: "David S. Miller" Cc: Cyrill Gorcunov Signed-off-by: Andrey Vagin Acked-by: Eric Dumazet Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_core.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index 8824ed0ccc9c..4d1fb5d094c3 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -312,6 +312,21 @@ static void death_by_timeout(unsigned long ul_conntrack) nf_ct_delete((struct nf_conn *)ul_conntrack, 0, 0); } +static inline bool +nf_ct_key_equal(struct nf_conntrack_tuple_hash *h, + const struct nf_conntrack_tuple *tuple, + u16 zone) +{ + struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(h); + + /* A conntrack can be recreated with the equal tuple, + * so we need to check that the conntrack is confirmed + */ + return nf_ct_tuple_equal(tuple, &h->tuple) && + nf_ct_zone(ct) == zone && + nf_ct_is_confirmed(ct); +} + /* * Warning : * - Caller must take a reference on returned object @@ -333,8 +348,7 @@ ____nf_conntrack_find(struct net *net, u16 zone, local_bh_disable(); begin: hlist_nulls_for_each_entry_rcu(h, n, &net->ct.hash[bucket], hnnode) { - if (nf_ct_tuple_equal(tuple, &h->tuple) && - nf_ct_zone(nf_ct_tuplehash_to_ctrack(h)) == zone) { + if (nf_ct_key_equal(h, tuple, zone)) { NF_CT_STAT_INC(net, found); local_bh_enable(); return h; @@ -372,8 +386,7 @@ begin: !atomic_inc_not_zero(&ct->ct_general.use))) h = NULL; else { - if (unlikely(!nf_ct_tuple_equal(tuple, &h->tuple) || - nf_ct_zone(ct) != zone)) { + if (unlikely(!nf_ct_key_equal(h, tuple, zone))) { nf_ct_put(ct); goto begin; } -- 2.20.1