[PATCH] netfilter: nf_tables: fix register ordering

[Andrew Paniakin]

From: Florian Westphal <fw@xxxxxxxxx>

commit d209df3e7f7002d9099fdb0f6df0f972b4386a63 upstream

[ We hit the trace described in commit message with the
kselftest/nft_trans_stress.sh. This patch diverges from the upstream one
since kernel 4.14 does not have following symbols:
nft_chain_filter_init, nf_tables_flowtable_notifier ]

We must register nfnetlink ops last, as that exposes nf_tables to
userspace.  Without this, we could theoretically get nfnetlink request
before net->nft state has been initialized.

Fixes: 99633ab29b213 ("netfilter: nf_tables: complete net namespace support")
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
[apanyaki: backport to v4.14-stable]
Signed-off-by: Andrew Paniakin <apanyaki@xxxxxxxxxx>
---

[  163.471426] Call Trace:
[  163.474901]  netlink_dump+0x125/0x2d0
[  163.479081]  __netlink_dump_start+0x16a/0x1c0
[  163.483589]  nf_tables_gettable+0x151/0x180 [nf_tables]
[  163.488561]  ? nf_tables_gettable+0x180/0x180 [nf_tables]
[  163.493658]  nfnetlink_rcv_msg+0x222/0x250 [nfnetlink]
[  163.498608]  ? __skb_try_recv_datagram+0x114/0x180
[  163.503359]  ? nfnetlink_net_exit_batch+0x60/0x60 [nfnetlink]
[  163.508590]  netlink_rcv_skb+0x4d/0x130
[  163.512832]  nfnetlink_rcv+0x92/0x780 [nfnetlink]
[  163.517465]  ? netlink_recvmsg+0x202/0x3e0
[  163.521801]  ? __kmalloc_node_track_caller+0x31/0x290
[  163.526635]  ? copy_msghdr_from_user+0xd5/0x150
[  163.531216]  ? __netlink_lookup+0xd0/0x130
[  163.535536]  netlink_unicast+0x196/0x240
[  163.539759]  netlink_sendmsg+0x2da/0x400
[  163.544010]  sock_sendmsg+0x36/0x40
[  163.548030]  SYSC_sendto+0x10e/0x140
[  163.552119]  ? __audit_syscall_entry+0xbc/0x110
[  163.556741]  ? syscall_trace_enter+0x1df/0x2e0
[  163.561315]  ? __audit_syscall_exit+0x231/0x2b0
[  163.565857]  do_syscall_64+0x67/0x110
[  163.569930]  entry_SYSCALL_64_after_hwframe+0x59/0xbe

Reproduce with debug logs clearly shows the nft initialization issue exactly as
in ported patch description:
[   22.600051] nft load start
[   22.600858] nf_tables: (c) 2007-2009 Patrick McHardy <kaber@xxxxxxxxx>
[   22.601241] nf_tables_gettable start: ffff888527c10000
[   22.601271] register_pernet_subsys ffffffffa02ba0c0
[   22.601274] netns ops_init ffffffffa02ba0c0 ffffffff821aeec0
[   22.602506] nf_tables_dump_tables: ffff888527c10000
[   22.603187] af_info list init done: ffffffff821aeec0
[   22.604064] nf_tables_dump_tables: afi:           (null)
[   22.604077] BUG: unable to handle kernel
[   22.604820] netns ops_init end ffffffffa02ba0c0 ffffffff821aeec0
[   22.605698] NULL pointer dereference
[   22.606354] netns ops_init ffffffffa02ba0c0 ffff888527c10000

(gdb) p &init_net
$2 = (struct net *) 0xffffffff821aeec0 <init_net>
ffff888527c10000 is a testns1 namespaces

To reproduce this problem and test the fix I scripted following steps:
- start Qemu VM
- run nft_trans_stress.sh test
- check dmesg logs for NULL pointer dereference
- reboot via QMP and repeat

I tested the fix with our kernel regression tests (including kselftest) also.

 net/netfilter/nf_tables_api.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index c683a45b8ae53..65495b528290b 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -6032,18 +6032,25 @@ static int __init nf_tables_module_init(void)
 		goto err1;
 	}
 
-	err = nf_tables_core_module_init();
+	err = register_pernet_subsys(&nf_tables_net_ops);
 	if (err < 0)
 		goto err2;
 
-	err = nfnetlink_subsys_register(&nf_tables_subsys);
+	err = nf_tables_core_module_init();
 	if (err < 0)
 		goto err3;
 
+	/* must be last */
+	err = nfnetlink_subsys_register(&nf_tables_subsys);
+	if (err < 0)
+		goto err4;
+
 	pr_info("nf_tables: (c) 2007-2009 Patrick McHardy <kaber@xxxxxxxxx>\n");
-	return register_pernet_subsys(&nf_tables_net_ops);
-err3:
+	return err;
+err4:
 	nf_tables_core_module_exit();
+err3:
+	unregister_pernet_subsys(&nf_tables_net_ops);
 err2:
 	kfree(info);
 err1:
-- 
2.39.2