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

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Date:   Tue, 26 Jun 2018 21:02:09 +0900
From:   吉藤英明 <hideaki.yoshifuji@...aclelinux.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        David Miller <davem@...emloft.net>,
        network dev <netdev@...r.kernel.org>,
        linux-sctp@...r.kernel.org, yoshfuji <yoshfuji@...ux-ipv6.org>,
        吉藤英明 <hideaki.yoshifuji@...aclelinux.com>
Subject: Re: [PATCH net-next 3/5] sctp: add spp_ipv6_flowlabel and spp_dscp
 for sctp_paddrparams

2018-06-26 13:33 GMT+09:00 Xin Long <lucien.xin@...il.com>:
> On Tue, Jun 26, 2018 at 12:31 AM, Marcelo Ricardo Leitner
> <marcelo.leitner@...il.com> wrote:
>> Hi,
>>
>> On Tue, Jun 26, 2018 at 01:12:00AM +0900, 吉藤英明 wrote:
>>> Hi,
>>>
>>> 2018-06-25 22:03 GMT+09:00 Marcelo Ricardo Leitner <marcelo.leitner@...il.com>:
>>> > On Mon, Jun 25, 2018 at 07:28:47AM -0400, Neil Horman wrote:
>>> >> 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.
>>> >
>>> > That will happen, yes, but do we really care about being future-proof
>>> > here? I mean: if we also update such check(s) to support dealing with
>>> > smaller-than-supported structs, newer kernels will be able to run
>>> > programs built against the old struct, and the new one; while building
>>> > using newer headers and running on older kernel may fool the
>>> > application in other ways too (like enabling support for something
>>> > that is available on newer kernel and that is not present in the older
>>> > one).
>>>
>>> We should not break existing apps.
>>> We still accept apps of pre-2.4 era without sin6_scope_id
>>> (e.g., net/ipv6/af_inet6.c:inet6_bind()).
>>
>> Yes. That's what I tried to say. That is supporting an old app built
>> with old kernel headers and running on a newer kernel, and not the
>> other way around (an app built with fresh headers and running on an
>> old kernel).
> To make it, I will update the check like:
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 1df5d07..c949d8c 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -2715,13 +2715,18 @@ static int
> sctp_setsockopt_peer_addr_params(struct sock *sk,
>         struct sctp_sock        *sp = sctp_sk(sk);
>         int error;
>         int hb_change, pmtud_change, sackdelay_change;
> +       int plen = sizeof(params);
> +       int old_plen = plen - sizeof(u32) * 2;

if (optlen < offsetof(struct sctp_paddrparams, spp_ipv6_flowlabel))
maybe?

>
> -       if (optlen != sizeof(struct sctp_paddrparams))
> +       if (optlen != plen && optlen != old_plen)
>                 return -EINVAL;
>
>         if (copy_from_user(&params, optval, optlen))
>                 return -EFAULT;
>
> +       if (optlen == old_plen)
> +               params.spp_flags &= ~(SPP_DSCP | SPP_IPV6_FLOWLABEL);

I think we should return -EINVAL if size is not new one.

--yoshfuji

> +
>         /* Validate flags and value parameters. */
>         hb_change        = params.spp_flags & SPP_HB;
>         pmtud_change     = params.spp_flags & SPP_PMTUD;
> @@ -5591,10 +5596,13 @@ static int
> sctp_getsockopt_peer_addr_params(struct sock *sk, int len,
>         struct sctp_transport   *trans = NULL;
>         struct sctp_association *asoc = NULL;
>         struct sctp_sock        *sp = sctp_sk(sk);
> +       int plen = sizeof(params);
> +       int old_plen = plen - sizeof(u32) * 2;
>
> -       if (len < sizeof(struct sctp_paddrparams))
> +       if (len < old_plen)
>                 return -EINVAL;
> -       len = sizeof(struct sctp_paddrparams);
> +
> +       len = len >= plen ? plen : old_plen;
>         if (copy_from_user(&params, optval, len))
>                 return -EFAULT;
>
> does it look ok to you?