[Devel] [PATCHv2 RH7] ve/net/ip6tables: fix NULL ptr dereference at ip6t_unregister_table

[Dmitry Safonov]

We do not init raw table when IPTABLES6 is forbidden in VE.
So we shouldn't unregister/free it.

The following actions:
[root at s186 ~]# vzctl create 100
[root at s186 ~]# prlctl set 100 --netfilter disabled
[root at s186 ~]# prlctl start 100
Starting the CT...
The CT has been successfully started.
[root at s186 ~]# prlctl stop 100
Stopping the CT...

May lead to memory corruption/NULL pointer dereference:
[13990.985979] BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
[13990.995425] Workqueue: netns cleanup_net
[13990.996030] task: ffff880423302610 ti: ffff880422dd0000 task.ti: ffff880422dd0000
[13990.996637] RIP: 0010:[<ffffffffa051f178>]  [<ffffffffa051f178>] ip6t_unregister_table+0x18/0x80 [ip6_tables]
[13991.006983] Call Trace:
[13991.007581]  [<ffffffffa05d6055>] ip6table_raw_net_exit+0x15/0x20 [ip6table_raw]
[13991.008187]  [<ffffffff81527dc9>] ops_exit_list.isra.5+0x39/0x60
[13991.008788]  [<ffffffff81528f50>] cleanup_net+0x260/0x480
[13991.009380]  [<ffffffff8109ef4b>] process_one_work+0x17b/0x470
[13991.009980]  [<ffffffff8109fd1b>] worker_thread+0x11b/0x400
[13991.010576]  [<ffffffff8109fc00>] ? rescuer_thread+0x400/0x400
[13991.011150]  [<ffffffff810a779f>] kthread+0xcf/0xe0
[13991.011717]  [<ffffffff810a76d0>] ? create_kthread+0x60/0x60
[13991.012619]  [<ffffffff81643cd8>] ret_from_fork+0x58/0x90
[13991.013153]  [<ffffffff810a76d0>] ? create_kthread+0x60/0x60
[13991.013668] Code: c4 28 5b 41 5c 41 5d 5d c3 e8 d5 c2 b5 e0 0f 1f 44 00 00 0f 1f 44 00 00 55 48 89 e5 41 57 41 56 49 89 fe 48 89 f7 41 55 41 54 53 <4c> 8b 7e 20 e8 7f 5f 04 e1 4c 8d 68 58 49 89 c4 8b 00 4c 89 eb
[13991.014765] RIP  [<ffffffffa051f178>] ip6t_unregister_table+0x18/0x80 [ip6_tables]

Fixes: commit bff5233618d8 ("ve/net/ip6tables: fix autoloading of the
ip6table_raw module from CT")

https://jira.sw.ru/browse/PSBM-54244

Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
Cc: Kirill Tkhai <ktkhai at virtuozzo.com>
Signed-off-by: Dmitry Safonov <dsafonov at virtuozzo.com>
---
v2: make it safe for possible online ipt_mask reconfiguration,
    that may come with some day in future

 net/ipv6/netfilter/ip6table_raw.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/netfilter/ip6table_raw.c b/net/ipv6/netfilter/ip6table_raw.c
index 271835df64ce..e224abe3ba40 100644
--- a/net/ipv6/netfilter/ip6table_raw.c
+++ b/net/ipv6/netfilter/ip6table_raw.c
@@ -33,6 +33,10 @@ static struct nf_hook_ops *rawtable_ops __read_mostly;
 static int __net_init ip6table_raw_net_init(struct net *net)
 {
 	struct ip6t_replace *repl;
+	struct xt_table *ip6table_raw;
+
+	if (WARN_ON(net->ipv6.ip6table_raw))
+		net->ipv6.ip6table_raw = NULL;
 
 	if (!net_ipt_permitted(net, VE_IP_IPTABLES6))
 		return 0;
@@ -40,15 +44,19 @@ static int __net_init ip6table_raw_net_init(struct net *net)
 	repl = ip6t_alloc_initial_table(&packet_raw);
 	if (repl == NULL)
 		return -ENOMEM;
-	net->ipv6.ip6table_raw =
-		ip6t_register_table(net, &packet_raw, repl);
+	ip6table_raw = ip6t_register_table(net, &packet_raw, repl);
 	kfree(repl);
-	return PTR_RET(net->ipv6.ip6table_raw);
+
+	if (!IS_ERR(ip6table_raw))
+		net->ipv6.ip6table_raw = ip6table_raw;
+
+	return PTR_RET(ip6table_raw);
 }
 
 static void __net_exit ip6table_raw_net_exit(struct net *net)
 {
-	ip6t_unregister_table(net, net->ipv6.ip6table_raw);
+	if (net->ipv6.ip6table_raw)
+		ip6t_unregister_table(net, net->ipv6.ip6table_raw);
 }
 
 static struct pernet_operations ip6table_raw_net_ops = {
-- 
2.10.1