netdev - Re: [PATCH net-next v2 1/2] tcp: Remove unnecessary dst check in tcp_conn

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Message-ID: <CAMDZJNW_nqUm7LaKy5GJBKMhKV6GeZS_yAnUy+gT68NatT_EZg@mail.gmail.com>
Date:   Mon, 21 Aug 2017 21:24:57 +0800
From:   Tonghao Zhang <xiangxia.m.yue@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 1/2] tcp: Remove unnecessary dst check in tcp_conn_request.

Thanks,  yes  this is a bug. I found this bug exists from 3.17~ 4.13.
The commit is d94e0417

One question:  should I send a patch for each kernel version because
code conflicts ?

a patch for v4.12
a patch for v4.11
a patch for v4.10~v4.7
a patch for v4.6~v3.17

and
a patch for  net-next, because tcp_tw_recycle has been removed.

Thanks very much.

On Sun, Aug 20, 2017 at 12:25 PM, David Miller <davem@...emloft.net> wrote:
> From: Tonghao Zhang <xiangxia.m.yue@...il.com>
> Date: Wed, 16 Aug 2017 20:02:45 -0700
>
>> Because we remove the tcp_tw_recycle support in the commit
>> 4396e46187c ('tcp: remove tcp_tw_recycle') and also delete
>> the code 'af_ops->route_req' for sysctl_tw_recycle in tcp_conn_request.
>> Now when we call the 'af_ops->route_req', the dist always is
>> NULL, and we remove the unnecessay check.
>>
>> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
>
> This is a bug actually, rather than something to paper over
> by removing the check.
>
> Code earlier in this function needs a proper 'dst' in order to operate
> properly.
>
> There is a call to tcp_peer_is_proven() which must have a proper route
> to make the determination yet it will always be NULL.
>
> Please investigate what the code is doing and how a test became
> "unnecessary" over time before blindly removing it, thank you.