From: Xin Long <lucien.xin@xxxxxxxxx>
Date: Tue, 27 Nov 2018 19:11:50 +0800
> sctp_assoc_update_frag_point() should be called whenever asoc->pathmtu
> changes, but we missed one place in sctp_association_init(). It would
> cause frag_point is zero when sending data.
>
> As says in Jakub's reproducer, if sp->pathmtu is set by socketopt, the
> new asoc->pathmtu inherits it in sctp_association_init(). Later when
> transports are added and their pmtu >= asoc->pathmtu, it will never
> call sctp_assoc_update_frag_point() to set frag_point.
>
> This patch is to fix it by updating frag_point after asoc->pathmtu is
> set as sp->pathmtu in sctp_association_init(). Note that it moved them
> after sctp_stream_init(), as stream->si needs to be set first.
>
> Frag_point's calculation is also related with datachunk's type, so it
> needs to update frag_point when stream->si may be changed in
> sctp_process_init().
>
> v1->v2:
> - call sctp_assoc_update_frag_point() separately in sctp_process_init
> and sctp_association_init, per Marcelo's suggestion.
>
> Fixes: 2f5e3c9df693 ("sctp: introduce sctp_assoc_update_frag_point")
> Reported-by: Jakub Audykowicz <jakub.audykowicz@xxxxxxxxx>
> Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Applied and queued up for -stable back to v4.18
