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

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Date:   Sat, 30 Jun 2018 17:15:18 +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>
Subject: Re: [PATCH net-next 3/5] sctp: add spp_ipv6_flowlabel and spp_dscp
 for sctp_paddrparams

Hi,

2018-06-28 15:40 GMT+09:00 Xin Long <lucien.xin@...il.com>:
> On Tue, Jun 26, 2018 at 8:02 PM, 吉藤英明
> <hideaki.yoshifuji@...aclelinux.com> wrote:
>> 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?
> Hi, yoshfuji,
> offsetof() is better. thank you.
>
>>
>>>
>>> -       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.
> Sorry, if we returned  -EINVAL when size is the old one,
> how can we guarantee an old app built with old kernel
> headers and running on a newer kernel works well?
> or you meant?
> if ((params.spp_flags & (SPP_DSCP | SPP_IPV6_FLOWLABEL)) &&
>     optlen != plen)
>         return EINVAL;

Yes, I meant this (it should be -EINVAL though).


>
>>
>> --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?