netdev - Re: [PATCH] net: l2tp: fix reversed udp6 checksum flags

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Message-Id: <68A05363-981B-4BF8-96A7-7D60BE3A96A0@gmail.com>
Date:	Sat, 30 Apr 2016 05:22:15 +0800
From:	Wang Shanker <shankerwangmiao@...il.com>
To:	James Chapman <jchapman@...alix.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] net: l2tp: fix reversed udp6 checksum flags

Is there any further suggestion or review?

> 在 2016年4月29日，03:25，Wang Shanker <shankerwangmiao@...il.com> 写道：
> 
> I think this is a logic error, rather than a change to the default
> UDP checksum setting. As expected, take rx for example, the flag 
> `L2TP_ATTR_UDP_ZERO_CSUM6_RX` is not set by default, and udp6 
> checksum will be checked by default. The fact is that, not setting
> `L2TP_ATTR_UDP_ZERO_CSUM6_RX` leads to ignoring udp6 checksum. Such
> a behavior does not correspond to the name 
> “L2TP_ATTR_UDP_ZERO_CSUM6_RX”. As a result, I call it a logic error.
> 
>> 在 2016年4月29日，02:46，James Chapman <jchapman@...alix.com> 写道：
>> 
>> Some additional background on this: Wang found this when configuring
>> l2tp tunnels using "ip l2tp" between two systems and then one system
>> was upgraded. The tunnel failed to pass data because one side had UDP
>> checksums enabled and the other now had them disabled. It seems kernel
>> changes related to UDP checksums resulted in a change to the default
>> UDP checksum setting for L2TP tunnels when using IPv6. Unfortunately,
>> iproute2 doesn't let the user configure L2TP UDP checksum settings, so
>> without this fix, some users may see problems depending on the kernel
>> version differences on the L2TP peers. One for stable?
>> 
>> Acked-by: James Chapman <jchapman@...alix.com>
>> 
>> On 28 April 2016 at 18:29, Wang Shanker <shankerwangmiao@...il.com> wrote:
>>> This patch fixes a bug which causes the behavior of whether to ignore
>>> udp6 checksum of udp6 encapsulated l2tp tunnel contrary to what
>>> userspace program requests.
>>> 
>>> When the flag `L2TP_ATTR_UDP_ZERO_CSUM6_RX` is set by userspace, it is
>>> expected that udp6 checksums of received packets of the l2tp tunnel
>>> to create should be ignored. In `l2tp_netlink.c`:
>>> `l2tp_nl_cmd_tunnel_create()`, `cfg.udp6_zero_rx_checksums` is set
>>> according to the flag, and then passed to `l2tp_core.c`:
>>> `l2tp_tunnel_create()` and then `l2tp_tunnel_sock_create()`. In
>>> `l2tp_tunnel_sock_create()`, `udp_conf.use_udp6_rx_checksums` is set
>>> the same to `cfg.udp6_zero_rx_checksums`. However, if we want the
>>> checksum to be ignored, `udp_conf.use_udp6_rx_checksums` should be set
>>> to `false`, i.e. be set to the contrary. Similarly, the same should be
>>> done to `udp_conf.use_udp6_tx_checksums`.
>>> 
>>> Signed-off-by: Miao Wang <shankerwangmiao@...il.com>
>>> ---
>>> net/l2tp/l2tp_core.c | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>> 
>>> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
>>> index afca2eb..6edfa99 100644
>>> --- a/net/l2tp/l2tp_core.c
>>> +++ b/net/l2tp/l2tp_core.c
>>> @@ -1376,9 +1376,9 @@ static int l2tp_tunnel_sock_create(struct net *net,
>>>                       memcpy(&udp_conf.peer_ip6, cfg->peer_ip6,
>>>                              sizeof(udp_conf.peer_ip6));
>>>                       udp_conf.use_udp6_tx_checksums =
>>> -                           cfg->udp6_zero_tx_checksums;
>>> +                         ! cfg->udp6_zero_tx_checksums;
>>>                       udp_conf.use_udp6_rx_checksums =
>>> -                           cfg->udp6_zero_rx_checksums;
>>> +                         ! cfg->udp6_zero_rx_checksums;
>>>               } else
>>> #endif
>>>               {
>>> --
>>> 2.5.2
>>> 
>