diff mbox series

[net,v2,1/2] sctp: do not retransmit upon FragNeeded if PMTU discovery is disabled

Message ID f96c4b84a1d19d16424cca1eaafc382d4bcd313b.1515020059.git.marcelo.leitner@gmail.com
State Superseded, archived
Delegated to: David Miller
Headers show
Series SCTP PMTU discovery fixes | expand

Commit Message

'Marcelo Ricardo Leitner' Jan. 3, 2018, 10:59 p.m. UTC
Currently, if PMTU discovery is disabled on a given transport, but the
configured value is higher than the actual PMTU, it is likely that we
will get some icmp Frag Needed. The issue is, if PMTU discovery is
disabled, we won't update the information and will issue a
retransmission immediately, which may very well trigger another ICMP,
and another retransmission, leading to a loop.

The fix is to simply not trigger immediate retransmissions if PMTU
discovery is disabled on the given transport.

Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
---
 net/sctp/input.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

Comments

Xin Long Jan. 4, 2018, 4:52 a.m. UTC | #1
On Thu, Jan 4, 2018 at 6:59 AM, Marcelo Ricardo Leitner
<marcelo.leitner@gmail.com> wrote:
> Currently, if PMTU discovery is disabled on a given transport, but the
> configured value is higher than the actual PMTU, it is likely that we
> will get some icmp Frag Needed. The issue is, if PMTU discovery is
> disabled, we won't update the information and will issue a
> retransmission immediately, which may very well trigger another ICMP,
> and another retransmission, leading to a loop.
>
> The fix is to simply not trigger immediate retransmissions if PMTU
> discovery is disabled on the given transport.
>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> ---
>  net/sctp/input.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index 621b5ca3fd1c17c3d7ef7bb1c7677ab98cebbe77..4a8e76f4834c90de9398455862423e598b8354a7 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -399,13 +399,18 @@ void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
>                 return;
>         }
>
> -       if (t->param_flags & SPP_PMTUD_ENABLE) {
> -               /* Update transports view of the MTU */
> -               sctp_transport_update_pmtu(t, pmtu);
> +       if (!(t->param_flags & SPP_PMTUD_ENABLE))
> +               /* We can't allow retransmitting in such case, as the
> +                * retransmission would be sized just as before, and thus we
> +                * would get another icmp, and retransmit again.
> +                */
> +               return;
>
> -               /* Update association pmtu. */
> -               sctp_assoc_sync_pmtu(asoc);
> -       }
> +       /* Update transports view of the MTU */
> +       sctp_transport_update_pmtu(t, pmtu);
> +
> +       /* Update association pmtu. */
> +       sctp_assoc_sync_pmtu(asoc);
>
>         /* Retransmit with the new pmtu setting.
>          * Normally, if PMTU discovery is disabled, an ICMP Fragmentation
> --
> 2.14.3
>

commit 52ccb8e90c0ace233b8b740f2fc5de0dbd706b27
Author: Frank Filz <ffilz@us.ibm.com>
Date:   Thu Dec 22 11:36:46 2005 -0800

    [SCTP]: Update SCTP_PEER_ADDR_PARAMS socket option to the latest api draft.

It seemed intended to move sctp_retransmit out of 'if (SPP_PMTUD_ENABLE) {}'
on the above commit with some notes:

        /* Retransmit with the new pmtu setting.
         * Normally, if PMTU discovery is disabled, an ICMP Fragmentation
         * Needed will never be sent, but if a message was sent before
         * PMTU discovery was disabled that was larger than the PMTU, it
         * would not be fragmented, so it must be re-transmitted fragmented.
         */

But this patch is equivalent to move it back into 'if (SPP_PMTUD_ENABLE) {}'.
will there be no regression caused?
'Marcelo Ricardo Leitner' Jan. 4, 2018, 11:23 a.m. UTC | #2
On Thu, Jan 04, 2018 at 12:52:32PM +0800, Xin Long wrote:
> On Thu, Jan 4, 2018 at 6:59 AM, Marcelo Ricardo Leitner
> <marcelo.leitner@gmail.com> wrote:
> > Currently, if PMTU discovery is disabled on a given transport, but the
> > configured value is higher than the actual PMTU, it is likely that we
> > will get some icmp Frag Needed. The issue is, if PMTU discovery is
> > disabled, we won't update the information and will issue a
> > retransmission immediately, which may very well trigger another ICMP,
> > and another retransmission, leading to a loop.
> >
> > The fix is to simply not trigger immediate retransmissions if PMTU
> > discovery is disabled on the given transport.
> >
> > Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> > ---
> >  net/sctp/input.c | 17 +++++++++++------
> >  1 file changed, 11 insertions(+), 6 deletions(-)
> >
> > diff --git a/net/sctp/input.c b/net/sctp/input.c
> > index 621b5ca3fd1c17c3d7ef7bb1c7677ab98cebbe77..4a8e76f4834c90de9398455862423e598b8354a7 100644
> > --- a/net/sctp/input.c
> > +++ b/net/sctp/input.c
> > @@ -399,13 +399,18 @@ void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
> >                 return;
> >         }
> >
> > -       if (t->param_flags & SPP_PMTUD_ENABLE) {
> > -               /* Update transports view of the MTU */
> > -               sctp_transport_update_pmtu(t, pmtu);
> > +       if (!(t->param_flags & SPP_PMTUD_ENABLE))
> > +               /* We can't allow retransmitting in such case, as the
> > +                * retransmission would be sized just as before, and thus we
> > +                * would get another icmp, and retransmit again.
> > +                */
> > +               return;
> >
> > -               /* Update association pmtu. */
> > -               sctp_assoc_sync_pmtu(asoc);
> > -       }
> > +       /* Update transports view of the MTU */
> > +       sctp_transport_update_pmtu(t, pmtu);
> > +
> > +       /* Update association pmtu. */
> > +       sctp_assoc_sync_pmtu(asoc);
> >
> >         /* Retransmit with the new pmtu setting.
> >          * Normally, if PMTU discovery is disabled, an ICMP Fragmentation
> > --
> > 2.14.3
> >
> 
> commit 52ccb8e90c0ace233b8b740f2fc5de0dbd706b27
> Author: Frank Filz <ffilz@us.ibm.com>
> Date:   Thu Dec 22 11:36:46 2005 -0800
> 
>     [SCTP]: Update SCTP_PEER_ADDR_PARAMS socket option to the latest api draft.
> 
> It seemed intended to move sctp_retransmit out of 'if (SPP_PMTUD_ENABLE) {}'
> on the above commit with some notes:

Good point.

> 
>         /* Retransmit with the new pmtu setting.
>          * Normally, if PMTU discovery is disabled, an ICMP Fragmentation
>          * Needed will never be sent, but if a message was sent before
>          * PMTU discovery was disabled that was larger than the PMTU, it
>          * would not be fragmented, so it must be re-transmitted fragmented.
>          */
> 
> But this patch is equivalent to move it back into 'if (SPP_PMTUD_ENABLE) {}'.
> will there be no regression caused?

I don't think this comment has been effective because the function
starts with:

void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
                           struct sctp_transport *t, __u32 pmtu)
{
        if (!t || (t->pathmtu <= pmtu))
                return;

So if the application managed to adjust pmtu after sending some data,
t->pathmtu will fit this check and nothing would be done anyway.

commit 91bd6b1e030266cf87d3f567b49f0fa60a7318ba
Author: Wei Yongjun <yjwei@cn.fujitsu.com>
Date:   Thu Oct 23 00:59:52 2008 -0700

    sctp: Drop ICMP packet too big message with MTU larger than
    current PMTU

I guess I should have removed this comment too. WDYT?
I'll prepare a v3 meanwhile.
Xin Long Jan. 4, 2018, 1:29 p.m. UTC | #3
On Thu, Jan 4, 2018 at 7:23 PM, Marcelo Ricardo Leitner
<marcelo.leitner@gmail.com> wrote:
> On Thu, Jan 04, 2018 at 12:52:32PM +0800, Xin Long wrote:
>> On Thu, Jan 4, 2018 at 6:59 AM, Marcelo Ricardo Leitner
>> <marcelo.leitner@gmail.com> wrote:
>> > Currently, if PMTU discovery is disabled on a given transport, but the
>> > configured value is higher than the actual PMTU, it is likely that we
>> > will get some icmp Frag Needed. The issue is, if PMTU discovery is
>> > disabled, we won't update the information and will issue a
>> > retransmission immediately, which may very well trigger another ICMP,
>> > and another retransmission, leading to a loop.
>> >
>> > The fix is to simply not trigger immediate retransmissions if PMTU
>> > discovery is disabled on the given transport.
>> >
>> > Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
>> > ---
>> >  net/sctp/input.c | 17 +++++++++++------
>> >  1 file changed, 11 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/net/sctp/input.c b/net/sctp/input.c
>> > index 621b5ca3fd1c17c3d7ef7bb1c7677ab98cebbe77..4a8e76f4834c90de9398455862423e598b8354a7 100644
>> > --- a/net/sctp/input.c
>> > +++ b/net/sctp/input.c
>> > @@ -399,13 +399,18 @@ void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
>> >                 return;
>> >         }
>> >
>> > -       if (t->param_flags & SPP_PMTUD_ENABLE) {
>> > -               /* Update transports view of the MTU */
>> > -               sctp_transport_update_pmtu(t, pmtu);
>> > +       if (!(t->param_flags & SPP_PMTUD_ENABLE))
>> > +               /* We can't allow retransmitting in such case, as the
>> > +                * retransmission would be sized just as before, and thus we
>> > +                * would get another icmp, and retransmit again.
>> > +                */
>> > +               return;
>> >
>> > -               /* Update association pmtu. */
>> > -               sctp_assoc_sync_pmtu(asoc);
>> > -       }
>> > +       /* Update transports view of the MTU */
>> > +       sctp_transport_update_pmtu(t, pmtu);
>> > +
>> > +       /* Update association pmtu. */
>> > +       sctp_assoc_sync_pmtu(asoc);
>> >
>> >         /* Retransmit with the new pmtu setting.
>> >          * Normally, if PMTU discovery is disabled, an ICMP Fragmentation
>> > --
>> > 2.14.3
>> >
>>
>> commit 52ccb8e90c0ace233b8b740f2fc5de0dbd706b27
>> Author: Frank Filz <ffilz@us.ibm.com>
>> Date:   Thu Dec 22 11:36:46 2005 -0800
>>
>>     [SCTP]: Update SCTP_PEER_ADDR_PARAMS socket option to the latest api draft.
>>
>> It seemed intended to move sctp_retransmit out of 'if (SPP_PMTUD_ENABLE) {}'
>> on the above commit with some notes:
>
> Good point.
>
>>
>>         /* Retransmit with the new pmtu setting.
>>          * Normally, if PMTU discovery is disabled, an ICMP Fragmentation
>>          * Needed will never be sent, but if a message was sent before
>>          * PMTU discovery was disabled that was larger than the PMTU, it
>>          * would not be fragmented, so it must be re-transmitted fragmented.
>>          */
>>
>> But this patch is equivalent to move it back into 'if (SPP_PMTUD_ENABLE) {}'.
>> will there be no regression caused?
>
> I don't think this comment has been effective because the function
> starts with:
>
> void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
>                            struct sctp_transport *t, __u32 pmtu)
> {
>         if (!t || (t->pathmtu <= pmtu))
>                 return;
>
> So if the application managed to adjust pmtu after sending some data,
> t->pathmtu will fit this check and nothing would be done anyway.
>
> commit 91bd6b1e030266cf87d3f567b49f0fa60a7318ba
> Author: Wei Yongjun <yjwei@cn.fujitsu.com>
> Date:   Thu Oct 23 00:59:52 2008 -0700
>
>     sctp: Drop ICMP packet too big message with MTU larger than
>     current PMTU
>
> I guess I should have removed this comment too. WDYT?
Yes, I agree. Next time the retransmit could also fragment it, and
it actually rarely happens, so no need to do it that immediately.

> I'll prepare a v3 meanwhile.
diff mbox series

Patch

diff --git a/net/sctp/input.c b/net/sctp/input.c
index 621b5ca3fd1c17c3d7ef7bb1c7677ab98cebbe77..4a8e76f4834c90de9398455862423e598b8354a7 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -399,13 +399,18 @@  void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
 		return;
 	}
 
-	if (t->param_flags & SPP_PMTUD_ENABLE) {
-		/* Update transports view of the MTU */
-		sctp_transport_update_pmtu(t, pmtu);
+	if (!(t->param_flags & SPP_PMTUD_ENABLE))
+		/* We can't allow retransmitting in such case, as the
+		 * retransmission would be sized just as before, and thus we
+		 * would get another icmp, and retransmit again.
+		 */
+		return;
 
-		/* Update association pmtu. */
-		sctp_assoc_sync_pmtu(asoc);
-	}
+	/* Update transports view of the MTU */
+	sctp_transport_update_pmtu(t, pmtu);
+
+	/* Update association pmtu. */
+	sctp_assoc_sync_pmtu(asoc);
 
 	/* Retransmit with the new pmtu setting.
 	 * Normally, if PMTU discovery is disabled, an ICMP Fragmentation