Changing time causes ipv6 panics

[Kris Kennaway]

I ran ntpdate on an amd64 system with ipv6 enabled and a skewed clock
(ntpdate stepped it back by about an hour), and immediately got a
use-after-free panic in ifaddr.  When I rebooted with memguard enabled
on this malloc type and retried, I got this panic upon changing the
date forward, then back, then forward again (also note the garbage
return data from ntpdate):

# date 200606011200
Thu Jun  1 12:00:00 UTC 2006
# ntpdate ntp.apple.com
16 Jan 00:40:18 ntpdate[612]: step time server 17.254.0.28 offset -~9000pm6}9426375508.195959 sec
# date 200606011200
Thu Jun  1 12:00:00 UTC 2006

Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0xffffffff91bd2198
fault code              = supervisor write, protection violation
instruction pointer     = 0x8:0xffffffff80321346
stack pointer           = 0x10:0xffffffffbcfa1b60
frame pointer           = 0x10:0xffffffffbcfa1b90
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 14 (swi4: clock sio)
[thread pid 14 tid 100010 ]
Stopped at      nd6_timer+0x106:        movl    %eax,0x198(%rbx)
db> wh
Tracing pid 14 tid 100010 td 0xffffff03e15d6c30
nd6_timer() at nd6_timer+0x106
softclock() at softclock+0x279
ithread_execute_handlers() at ithread_execute_handlers+0x12f
ithread_loop() at ithread_loop+0x99
fork_exit() at fork_exit+0xdf
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffffffbcfa1d40, rbp = 0 ---

Unfortunately I can't dump on this system, but:

(kgdb) list *(nd6_timer+0x106)
0xffffffff80321346 is in nd6_timer (../../../netinet6/nd6.c:585).
580                                     goto addrloop; /* XXX: see below */
581                     }
582                     if (IFA6_IS_DEPRECATED(ia6)) {
583                             int oldflags = ia6->ia6_flags;
584
585                             ia6->ia6_flags |= IN6_IFF_DEPRECATED;
586
587                             /*
588                              * If a temporary address has just become deprecated,
589                              * regenerate a new one if possible.

Kris


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