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 12:33:37 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     吉藤英明 <hideaki.yoshifuji@...aclelinux.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

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 != 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);
+
        /* 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?