Re: [PATCH v5 1/2] sctp: check the rto_min and rto_max

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On 12/07/2013 08:01 PM, Vlad Yasevich wrote:
On 12/07/2013 07:43 AM, Daniel Borkmann wrote:
On 12/07/2013 08:17 AM, Wang Weidong wrote:
rto_min should be smaller than rto_max while rto_max should be larger
than rto_min. Add two proc_handler for the checking. Add the check in
sctp_setsockopt_rtoinfo.

Suggested-by: Vlad Yasevich <vyasevich@xxxxxxxxx>
Signed-off-by: Wang Weidong <wangweidong1@xxxxxxxxxx>
---

Thanks Wang, also for your second patch.

Second one looks good to me, thanks for the cleanup!

I was wondering where 86400000 comes from? Looking through the git
history didn't give much clues and the RFC4960 neither. Clearly,
section 15 of RFC4960 *recommends* as initial values ...

   RTO.Initial - 3 seconds
   RTO.Min - 1 second
   RTO.Max - 60 seconds

... which we have as constants in [1] and are assigned to globals
initially in [2,3] with those recommended values. That's all good.

But still [not *directly* related to your patch though], where does
86400000 come from? I expect that's for the max SCTP heartbeat
interval or max cookie lifetime?

No, initially it was defined as rto_timer_max and was the upper bound
for the rto timer.   When you think about it, it's a bit ridiculous
really.  What you are saying is that your rto timer is allowed to
grow as long as 1 day, so you would at an absolute maximum retransmit
one packet per day :)

Exactly, maybe initial SCTP implementors already took into account
we could have SCTP connections to other galaxies, but clearly untested
so far? :)

I think we should be absolutely fine with a max configurable upper
limit of twice the recommended RTO.Max value from the RFC.

I don't think this limit is specified anywhere as is though.  It
was something that's been there since the 2.5 days.

-vlad
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