Subject: Re: [PATCH] ip_tunnel: the lack of vti_link_ops' dellink() cause kernel panic

From: Nicolas Dichtel <[email-masked]>
Date: Mon, 24 Nov 2014 15:18:38 +0100

Le 23/11/2014 08:04, Xin Long a écrit :
> Now the vti_link_ops do not point the .dellink, for fb tunnel device
> (ip_vti0), the net_device will be removed as the default .dellink is
> unregister_netdevice_queue,but the tunnel still in the tunnel list,
> then if we add a new vti tunnel, in ip_tunnel_find():
>
>          hlist_for_each_entry_rcu(t, head, hash_node) {
>                  if (local == t->parms.iph.saddr &&
>                      remote == t->parms.iph.daddr &&
>                      link == t->parms.link &&
> ==>                 type == t->dev->type &&
>                      ip_tunnel_key_match(&t->parms, flags, key))
>                          break;
>          }
>
> the panic will happen, cause dev of ip_tunnel *t is null:
> [ 3835.072977] IP: [<ffffffffa04103fd>] ip_tunnel_find+0x9d/0xc0 [ip_tunnel]
> [ 3835.073008] PGD b2c21067 PUD b7277067 PMD 0
> [ 3835.073008] Oops: 0000 [#1] SMP
> .....
> [ 3835.073008] Stack:
> [ 3835.073008]  ffff8800b72d77f0 ffffffffa0411924 ffff8800bb956000 ffff8800b72d78e0
> [ 3835.073008]  ffff8800b72d78a0 0000000000000000 ffffffffa040d100 ffff8800b72d7858
> [ 3835.073008]  ffffffffa040b2e3 0000000000000000 0000000000000000 0000000000000000
> [ 3835.073008] Call Trace:
> [ 3835.073008]  [<ffffffffa0411924>] ip_tunnel_newlink+0x64/0x160 [ip_tunnel]
> [ 3835.073008]  [<ffffffffa040b2e3>] vti_newlink+0x43/0x70 [ip_vti]
> [ 3835.073008]  [<ffffffff8150d4da>] rtnl_newlink+0x4fa/0x5f0
> [ 3835.073008]  [<ffffffff812f68bb>] ? nla_strlcpy+0x5b/0x70
> [ 3835.073008]  [<ffffffff81508fb0>] ? rtnl_link_ops_get+0x40/0x60
> [ 3835.073008]  [<ffffffff8150d11f>] ? rtnl_newlink+0x13f/0x5f0
> [ 3835.073008]  [<ffffffff81509cf4>] rtnetlink_rcv_msg+0xa4/0x270
> [ 3835.073008]  [<ffffffff8126adf5>] ? sock_has_perm+0x75/0x90
> [ 3835.073008]  [<ffffffff81509c50>] ? rtnetlink_rcv+0x30/0x30
> [ 3835.073008]  [<ffffffff81529e39>] netlink_rcv_skb+0xa9/0xc0
> [ 3835.073008]  [<ffffffff81509c48>] rtnetlink_rcv+0x28/0x30
> ....
>
> modprobe ip_vti
> ip link del ip_vti0 type vti
> ip link add ip_vti0 type vti
> rmmod ip_vti
>
> do that one or more times, kernel will panic.
>
> fix it by assigning ip_tunnel_dellink to vti_link_ops' dellink, in
> which we skip the unregister of fb tunnel device. do the same on ip6_vti.
>
> Signed-off-by: Xin Long <[email-masked]>
> Signed-off-by: Cong Wang <[email-masked]>
> ---
>   net/ipv4/ip_vti.c  |  1 +
>   net/ipv6/ip6_vti.c | 11 +++++++++++
>   2 files changed, 12 insertions(+)
>
> diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
> index 3e86101..1a7e979 100644
> --- a/net/ipv4/ip_vti.c
> +++ b/net/ipv4/ip_vti.c
> @@ -528,6 +528,7 @@ static struct rtnl_link_ops vti_link_ops __read_mostly = {
>   	.validate	= vti_tunnel_validate,
>   	.newlink	= vti_newlink,
>   	.changelink	= vti_changelink,
> +	.dellink        = ip_tunnel_dellink,
Nitpicking: please, use a tab instead of space to align the '=', like other
lines.