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 [off-list ref]:

quoted

On Mon, Jun 25, 2018 at 07:28:47AM -0400, Neil Horman wrote:

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On Mon, Jun 25, 2018 at 04:31:26PM +0900, David Miller wrote:

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From: Xin Long <lucien.xin@gmail.com>
Date: Mon, 25 Jun 2018 10:14:35 +0800

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 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).

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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

It's more for supporting running 32-bits apps on 64-bit kernels
(according to 20c9c825b12fc).

  Marcelo