BIND 10 #2946: avoid handling DNSServer events after free

[BIND 10 Development]

#2946: avoid handling DNSServer events after free
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            Reporter:  jinmei        |                        Owner:
                Type:  defect        |  jinmei
            Priority:  medium        |                       Status:
           Component:  b10-auth      |  accepted
            Keywords:                |                    Milestone:
           Sensitive:  0             |  Sprint-20130528
         Sub-Project:  DNS           |                   Resolution:
Estimated Difficulty:  5             |                 CVSS Scoring:
         Total Hours:  0             |              Defect Severity:  N/A
                                     |  Feature Depending on Ticket:
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Comment (by jinmei):

 trac2946 is ready for review.

 the changes (except the last commit, see below) should be
 straightforward with the understanding the problem.

 regarding other servers than `SyncUDPServer`, on a closer lookup (+
 some experiments) I realized they don't have this issue, at least in
 an obvious way like the case of `SyncUDPServer`.  Other server
 implementations passes a copy of the server object, sharing actual
 resources via member shared_ptr's.

 I noticed one possible point of use-after-free in `TCPServer`, which
 was fixed in the last commit.  The change should be straightforward,
 although I couldn't come up with a reasonable test scenario to prove
 my theory.  So, if this is considered a premature change I'm okay with
 excluding it.

 proposed changelog:
 {{{
 614.?   [bug]           jinmei
         b10-auth: Avoid referencing to a freed object when authoritative
         server addresses are reconfigured.  It caused a crash on a busy
         server during initial startup time, and the same crash could also
         happen if listen_on parameters are reconfigured run time.
         (Trac #2946, git TBD)
 }}}

-- 
Ticket URL: <http://bind10.isc.org/ticket/2946#comment:4>
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