netdev - Re: [Patch net-next] call sk_dst_reset when set SO

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Message-ID: <CANn89i+THvVsLvLnWbQO052vtuY2C1R9thEioRQbcsEDtuANgA@mail.gmail.com>
Date:   Wed, 5 Dec 2018 15:17:21 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     yupeng0921@...il.com
Cc:     netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>
Subject: Re: [Patch net-next] call sk_dst_reset when set SO_DONTROUTE

On Wed, Dec 5, 2018 at 3:07 PM yupeng <yupeng0921@...il.com> wrote:
>
> after set SO_DONTROUTE to 1, the IP layer should not route packets if
> the dest IP address is not in link scope. But if the socket has cached
> the dst_entry, such packets would be routed until the sk_dst_cache
> expires. So we should clean the sk_dst_cache when a user set
> SO_DONTROUTE option. Below are server/client python scripts which
> could reprodue this issue:
>
> server side code:
> ==========================================================================
> import socket
> import struct
>
> s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
> s.bind(('0.0.0.0', 9000))
> s.listen(1)
> sock, addr = s.accept()
> sock.setsockopt(socket.SOL_SOCKET, socket.SO_DONTROUTE, struct.pack('i', 1))
> while True:
>     data = sock.recv(1024) # here the sock.recv should not return anything

Why is that so ?

What is the relation of input path with the SO_DONTROUTE which is for TX ?

sk_dst_reset(sk) should not impact receive side ?

Thanks for providing a test !

>     print(data)
> ==========================================================================
>
> client side code:
> ==========================================================================
> import socket
> import time
>
> s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
> s.connect(('server_address', 9000))
> while True:
>     s.send(b'foo')
>     print('send foo')
>     time.sleep(1)
> ==========================================================================
>
> Signed-off-by: yupeng <yupeng0921@...il.com>
> ---
>  net/core/sock.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index f5bb89785e47..f00902c532cc 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -700,6 +700,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
>                 break;
>         case SO_DONTROUTE:
>                 sock_valbool_flag(sk, SOCK_LOCALROUTE, valbool);
> +               sk_dst_reset(sk);
>                 break;
>         case SO_BROADCAST:
>                 sock_valbool_flag(sk, SOCK_BROADCAST, valbool);
> --
> 2.17.1
>