On 01/07/2014 02:31 PM, Andrey Vagin wrote: > 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 node. > In our case one conntrack is initialized from a few tasks concurrently, > we don't have any other explanation for this. I would add; this strange traffic is generated by botnet clients (/etc/atdd and /boot/.IptabLes) Several threads are send lot of identical tcp packets via RAW socket. https://bugzilla.openvz.org/show_bug.cgi?id=2851 > <2>[46267.083061] kernel BUG at net/ipv4/netfilter/nf_nat_core.c:322! > ... > <4>[46267.083951] RIP: 0010:[<ffffffffa01e00a4>] [<ffffffffa01e00a4>] nf_nat_setup_info+0x564/0x590 [nf_nat] > ... > <4>[46267.085549] Call Trace: > <4>[46267.085622] [<ffffffffa023421b>] alloc_null_binding+0x5b/0xa0 [iptable_nat] > <4>[46267.085697] [<ffffffffa02342bc>] nf_nat_rule_find+0x5c/0x80 [iptable_nat] > <4>[46267.085770] [<ffffffffa0234521>] nf_nat_fn+0x111/0x260 [iptable_nat] > <4>[46267.085843] [<ffffffffa0234798>] nf_nat_out+0x48/0xd0 [iptable_nat] > <4>[46267.085919] [<ffffffff814841b9>] nf_iterate+0x69/0xb0 > <4>[46267.085991] [<ffffffff81494e70>] ? ip_finish_output+0x0/0x2f0 > <4>[46267.086063] [<ffffffff81484374>] nf_hook_slow+0x74/0x110 > <4>[46267.086133] [<ffffffff81494e70>] ? ip_finish_output+0x0/0x2f0 > <4>[46267.086207] [<ffffffff814b5890>] ? dst_output+0x0/0x20 > <4>[46267.086277] [<ffffffff81495204>] ip_output+0xa4/0xc0 > <4>[46267.086346] [<ffffffff814b65a4>] raw_sendmsg+0x8b4/0x910 > <4>[46267.086419] [<ffffffff814c10fa>] inet_sendmsg+0x4a/0xb0 > <4>[46267.086491] [<ffffffff814459aa>] ? sock_update_classid+0x3a/0x50 > <4>[46267.086562] [<ffffffff81444d67>] sock_sendmsg+0x117/0x140 > <4>[46267.086638] [<ffffffff8151997b>] ? _spin_unlock_bh+0x1b/0x20 > <4>[46267.086712] [<ffffffff8109d370>] ? autoremove_wake_function+0x0/0x40 > <4>[46267.086785] [<ffffffff81495e80>] ? do_ip_setsockopt+0x90/0xd80 > <4>[46267.086858] [<ffffffff8100be0e>] ? call_function_interrupt+0xe/0x20 > <4>[46267.086936] [<ffffffff8118cb10>] ? ub_slab_ptr+0x20/0x90 > <4>[46267.087006] [<ffffffff8118cb10>] ? ub_slab_ptr+0x20/0x90 > <4>[46267.087081] [<ffffffff8118f2e8>] ? kmem_cache_alloc+0xd8/0x1e0 > <4>[46267.087151] [<ffffffff81445599>] sys_sendto+0x139/0x190 > <4>[46267.087229] [<ffffffff81448c0d>] ? sock_setsockopt+0x16d/0x6f0 > <4>[46267.087303] [<ffffffff810efa47>] ? audit_syscall_entry+0x1d7/0x200 > <4>[46267.087378] [<ffffffff810ef795>] ? __audit_syscall_exit+0x265/0x290 > <4>[46267.087454] [<ffffffff81474885>] ? compat_sys_setsockopt+0x75/0x210 > <4>[46267.087531] [<ffffffff81474b5f>] compat_sys_socketcall+0x13f/0x210 > <4>[46267.087607] [<ffffffff8104dea3>] 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 [<ffffffffa01e00a4>] nf_nat_setup_info+0x564/0x590 > > Cc: Florian Westphal <fw@xxxxxxxxx> > Cc: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> > Cc: Patrick McHardy <kaber@xxxxxxxxx> > Cc: Jozsef Kadlecsik <kadlec@xxxxxxxxxxxxxxxxx> > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> > Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx> > Signed-off-by: Andrey Vagin <avagin@xxxxxxxxxx> > --- > net/netfilter/nf_conntrack_core.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c > index 43549eb..7a34bb2 100644 > --- a/net/netfilter/nf_conntrack_core.c > +++ b/net/netfilter/nf_conntrack_core.c > @@ -387,8 +387,12 @@ begin: > !atomic_inc_not_zero(&ct->ct_general.use))) > h = NULL; > else { > + /* A conntrack can be recreated with the equal tuple, > + * so we need to check that the conntrack is initialized > + */ > if (unlikely(!nf_ct_tuple_equal(tuple, &h->tuple) || > - nf_ct_zone(ct) != zone)) { > + nf_ct_zone(ct) != zone) || > + !nf_ct_is_confirmed(ct)) { > nf_ct_put(ct); > goto begin; > } > -- To unsubscribe from this list: send the line "unsubscribe netfilter" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
