On Tue, Oct 6, 2020 at 3:01 AM Marcelo Ricardo Leitner
[off-list ref] wrote:

On Sat, Oct 03, 2020 at 08:24:34PM +0800, Xin Long wrote:

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On Sat, Oct 3, 2020 at 7:23 PM Xin Long [off-list ref] wrote:

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On Sat, Oct 3, 2020 at 4:12 PM Xin Long [off-list ref] wrote:

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On Sat, Oct 3, 2020 at 12:08 PM Marcelo Ricardo Leitner
[off-list ref] wrote:

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On Wed, Sep 30, 2020 at 03:00:42AM +0800, kernel test robot wrote:

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Hi Xin,

Thank you for the patch! Yet something to improve:

I wonder how are you planning to fix this. It is quite entangled.
This is not performance critical. Maybe the cleanest way out is to
move it to a .c file.

Adding a
#if defined(CONFIG_IP_SCTP) || defined(CONFIG_IP_SCTP_MODULE)
in there doesn't seem good.

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   In file included from include/net/sctp/checksum.h:27,
                    from net/netfilter/nf_nat_proto.c:16:
   include/net/sctp/sctp.h: In function 'sctp_mtu_payload':

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include/net/sctp/sctp.h:583:31: error: 'struct net' has no member named 'sctp'; did you mean 'ct'?

     583 |   if (sock_net(&sp->inet.sk)->sctp.udp_port)
         |                               ^~~~
         |                               ct

Here is actually another problem, I'm still thinking how to fix it.

Now sctp_mtu_payload() returns different value depending on
net->sctp.udp_port. but net->sctp.udp_port can be changed by
"sysctl -w" anytime. so:

Good point.

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In sctp_packet_config() it gets overhead/headroom by calling
sctp_mtu_payload(). When 'udp_port' is 0, it's IP+MAC header
size. Then if 'udp_port' is changed to 9899 by 'sysctl -w',
udphdr will also be added to the packet in sctp_v4_xmit(),
and later the headroom may not be enough for IP+MAC headers.

I'm thinking to add sctp_sock->udp_port, and it'll be set when
the sock is created with net->udp_port. but not sure if we should
update sctp_sock->udp_port with  net->udp_port when sending packets?

I don't think so,

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something like:

...

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diff --git a/net/sctp/output.c b/net/sctp/output.c
index 6614c9fdc51e..c96b13ec72f4 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c

@@ -91,6 +91,14 @@ void sctp_packet_config(struct sctp_packet *packet,

__u32 vtag,
        if (asoc) {
                sk = asoc->base.sk;
                sp = sctp_sk(sk);
+
+               if (unlikely(sp->udp_port != sock_net(sk)->sctp.udp_port)) {

RFC6951 has:

6.1.  Get or Set the Remote UDP Encapsulation Port Number
      (SCTP_REMOTE_UDP_ENCAPS_PORT)
...
   sue_assoc_id:  This parameter is ignored for one-to-one style
      sockets.  For one-to-many style sockets, the application may fill
      in an association identifier or SCTP_FUTURE_ASSOC for this query.
      It is an error to use SCTP_{CURRENT|ALL}_ASSOC in sue_assoc_id.

   sue_address:  This specifies which address is of interest.  If a
      wildcard address is provided, it applies only to future paths.

So I'm not seeing a reason to have a system wide knob that takes
effect in run time like this.
Enable, start apps, and they keep behaving as initially configured.
Need to disable? Restart the apps/sockets.

Thoughts?

Right, not to update it on tx path makes more sense. Thanks.

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+                       __u16 port = sock_net(sk)->sctp.udp_port;
+
+                       if (!sp->udp_port || !port)
+                               sctp_assoc_update_frag_point(asoc);
+                       sp->udp_port = port;
+               }
        }