[Devel] [PATCH RHEL7 COMMIT] ve/net/ip6tables: fix NULL ptr dereference at ip6t_unregister_table

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.36.1.vz7.19.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.36.1.vz7.19.7
------>
commit aeb1f3c315dff548a54c6fcda9d34034322c6f98
Author: Dmitry Safonov <dsafonov at virtuozzo.com>
Date:   Mon Nov 14 13:14:56 2016 +0400

    ve/net/ip6tables: fix NULL ptr dereference at ip6t_unregister_table
    
    We do not init raw table when IPTABLES6 is forbidden in CT.
    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
    
    Signed-off-by: Dmitry Safonov <dsafonov at virtuozzo.com>
    Acked-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    Acked-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 net/ipv6/netfilter/ip6table_raw.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/netfilter/ip6table_raw.c b/net/ipv6/netfilter/ip6table_raw.c
index 271835d..b23d6c9 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 +44,23 @@ 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)
 {
+	if (!net->ipv6.ip6table_raw)
+		return;
+
 	ip6t_unregister_table(net, net->ipv6.ip6table_raw);
+
+	net->ipv6.ip6table_raw = NULL;
 }
 
 static struct pernet_operations ip6table_raw_net_ops = {