netdev - Re: [PATCH net-next 3/5] sctp: add spp_ipv6_flowlabel and spp_dscp for sctp

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Message-ID: <20180625112847.GB16772@hmswarspite.think-freely.org>
Date:   Mon, 25 Jun 2018 07:28:47 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     David Miller <davem@...emloft.net>
Cc:     lucien.xin@...il.com, netdev@...r.kernel.org,
        linux-sctp@...r.kernel.org, marcelo.leitner@...il.com
Subject: Re: [PATCH net-next 3/5] sctp: add spp_ipv6_flowlabel and spp_dscp
 for sctp_paddrparams

On Mon, Jun 25, 2018 at 04:31:26PM +0900, David Miller wrote:
> From: Xin Long <lucien.xin@...il.com>
> Date: Mon, 25 Jun 2018 10:14:35 +0800
> 
> >  struct sctp_paddrparams {
> > @@ -773,6 +775,8 @@ struct sctp_paddrparams {
> >  	__u32			spp_pathmtu;
> >  	__u32			spp_sackdelay;
> >  	__u32			spp_flags;
> > +	__u32			spp_ipv6_flowlabel;
> > +	__u8			spp_dscp;
> >  } __attribute__((packed, aligned(4)));
> 
> I don't think you can change the size of this structure like this.
> 
> This check in sctp_setsockopt_peer_addr_params():
> 
> 	if (optlen != sizeof(struct sctp_paddrparams))
> 		return -EINVAL;
> 
> is going to trigger in old kernels when executing programs
> built against the new struct definition.
> 
I think thats also the reason its a packed aligned attribute, it can't be
changed, or older kernels won't be able to fill it out properly.
Neil