Hi,
2018-06-25 22:03 GMT+09:00 Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>:
> 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@xxxxxxxxx>
>> > 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()).
>
>> >
>> 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
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