netdev - Re: [PATCH iproute2] ss: do not emit warn while dumping MPTCP on old kernels

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Date:   Wed, 27 Jan 2021 13:30:04 +0000
From:   "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@...ia.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>
CC:     "dsahern@...nel.org" <dsahern@...nel.org>
Subject: Re: [PATCH iproute2] ss: do not emit warn while dumping MPTCP on old
 kernels

On Mon, 2021-01-25 at 17:02 +0100, Paolo Abeni wrote:
> Prior to this commit, running 'ss' on a kernel older than v5.9
> bumps an error message:
> 
> RTNETLINK answers: Invalid argument

Thanks, works perfectly for me.
-Tommi

> When asked to dump protocol number > 255 - that is: MPTCP - 'ss'
> adds an INET_DIAG_REQ_PROTOCOL attribute, unsupported by the older
> kernel.
> 
> Avoid the warning ignoring filter issues when INET_DIAG_REQ_PROTOCOL
> is used.
> 
> Additionally older kernel end-up invoking tcpdiag_send(), which
> in turn will try to dump DCCP socks. Bail early in such function,
> as the kernel does not implement an MPTCPDIAG_GET request.
> 
> Reported-by: "Rantala, Tommi T. (Nokia - FI/Espoo)" <
> tommi.t.rantala@...ia.com>
> Fixes: 9c3be2c0eee0 ("ss: mptcp: add msk diag interface support")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
>  misc/ss.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/misc/ss.c b/misc/ss.c
> index 0593627b..ad46f9db 100644
> --- a/misc/ss.c
> +++ b/misc/ss.c
> @@ -3404,7 +3404,7 @@ static int tcpdiag_send(int fd, int protocol, struct
> filter *f)
>  	struct iovec iov[3];
>  	int iovlen = 1;
>  
> -	if (protocol == IPPROTO_UDP)
> +	if (protocol == IPPROTO_UDP || protocol == IPPROTO_MPTCP)
>  		return -1;
>  
>  	if (protocol == IPPROTO_TCP)
> @@ -3623,6 +3623,14 @@ static int inet_show_netlink(struct filter *f, FILE
> *dump_fp, int protocol)
>  	if (preferred_family == PF_INET6)
>  		family = PF_INET6;
>  
> +	/* extended protocol will use INET_DIAG_REQ_PROTOCOL,
> +	 * not supported by older kernels. On such kernel
> +	 * rtnl_dump will bail with rtnl_dump_error().
> +	 * Suppress the error to avoid confusing the user
> +	 */
> +	if (protocol > 255)
> +		rth.flags |= RTNL_HANDLE_F_SUPPRESS_NLERR;
> +
>  again:
>  	if ((err = sockdiag_send(family, rth.fd, protocol, f)))
>  		goto Exit;