netdev - [PATCH net] ip6_tunnel: do not allow loading ip6

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Date:   Fri, 15 Sep 2017 15:58:33 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     network dev <netdev@...r.kernel.org>
Cc:     davem@...emloft.net, Dmitry Kozlov <xeb@...l.ru>, jbenc@...hat.com
Subject: [PATCH net] ip6_tunnel: do not allow loading ip6_tunnel if ipv6 is disabled in cmdline

If ipv6 has been disabled from cmdline since kernel started, it makes
no sense to allow users to create any ip6 tunnel. Otherwise, it could
some potential problem.

Jianlin found a kernel crash caused by this in ip6_gre when he set
ipv6.disable=1 in grub:

[  209.588865] Unable to handle kernel paging request for data at address 0x00000080
[  209.588872] Faulting instruction address: 0xc000000000a3aa6c
[  209.588879] Oops: Kernel access of bad area, sig: 11 [#1]
[  209.589062] NIP [c000000000a3aa6c] fib_rules_lookup+0x4c/0x260
[  209.589071] LR [c000000000b9ad90] fib6_rule_lookup+0x50/0xb0
[  209.589076] Call Trace:
[  209.589097] fib6_rule_lookup+0x50/0xb0
[  209.589106] rt6_lookup+0xc4/0x110
[  209.589116] ip6gre_tnl_link_config+0x214/0x2f0 [ip6_gre]
[  209.589125] ip6gre_newlink+0x138/0x3a0 [ip6_gre]
[  209.589134] rtnl_newlink+0x798/0xb80
[  209.589142] rtnetlink_rcv_msg+0xec/0x390
[  209.589151] netlink_rcv_skb+0x138/0x150
[  209.589159] rtnetlink_rcv+0x48/0x70
[  209.589169] netlink_unicast+0x538/0x640
[  209.589175] netlink_sendmsg+0x40c/0x480
[  209.589184] ___sys_sendmsg+0x384/0x4e0
[  209.589194] SyS_sendmsg+0xd4/0x140
[  209.589201] SyS_socketcall+0x3e0/0x4f0
[  209.589209] system_call+0x38/0xe0

This patch is to return -EOPNOTSUPP in ip6_tunnel_init if ipv6 has been
disabled from cmdline.

Reported-by: Jianlin Shi <jishi@...hat.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 net/ipv6/ip6_tunnel.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index ae73164..f2f21c2 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -2259,6 +2259,9 @@ static int __init ip6_tunnel_init(void)
 {
 	int  err;
 
+	if (!ipv6_mod_enabled())
+		return -EOPNOTSUPP;
+
 	err = register_pernet_device(&ip6_tnl_net_ops);
 	if (err < 0)
 		goto out_pernet;
-- 
2.1.0