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Message-ID: <CAOxq_8OgMiH8L9pvXdZPsPUjgcx67QoE08V8unDHHBgw8=D3DQ@mail.gmail.com>
Date: Sat, 24 Oct 2015 11:31:17 -0700
From: Ani Sinha <ani@...sta.com>
To: Pablo Neira Ayuso <pablo@...filter.org>,
Patrick McHardy <kaber@...sh.net>,
"David S. Miller" <davem@...emloft.net>,
netfilter-devel@...r.kernel.org, coreteam@...filter.org,
Ani Sinha <ani@...rban.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
Florian Westphal <fw@...len.de>
Subject: Re: [PATCH 1/1] commit c6825c0976fa7893692e0e43b09740b419b23c09 upstream.
Please refer to the thread "linux 3.4.43 : kernel crash at
__nf_conntrack_confirm" on netdev for context.
thanks
On Sat, Oct 24, 2015 at 11:27 AM, Ani Sinha <ani@...sta.com> wrote:
> 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:[<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: Eric Dumazet <eric.dumazet@...il.com>
> Cc: Florian Westphal <fw@...len.de>
> Cc: Pablo Neira Ayuso <pablo@...filter.org>
> Cc: Patrick McHardy <kaber@...sh.net>
> Cc: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> Signed-off-by: Andrey Vagin <avagin@...nvz.org>
> Acked-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
> Signed-off-by: Ani Sinha <ani@...sta.com>
> ---
> 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 9a46908..fd0f7a3 100644
> --- a/net/netfilter/nf_conntrack_core.c
> +++ b/net/netfilter/nf_conntrack_core.c
> @@ -309,6 +309,21 @@ static void death_by_timeout(unsigned long ul_conntrack)
> nf_ct_put(ct);
> }
>
> +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
> @@ -330,8 +345,7 @@ ____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;
> @@ -378,8 +392,7 @@ 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;
> }
> --
> 1.8.1.4
>
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