[Bug 230242] SCTP uses deprecated IPv6 addresses

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=230242

            Bug ID: 230242
           Summary: SCTP uses deprecated IPv6 addresses
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: timo.voelker at fh-muenster.de

My router sometimes sends IPv6 Prefixes with a lifetime of 0. My FreeBSD box
creates an IPv6 address from the prefix and adds it as deprecated address to
the interface. So far so good.

The problem is that SCTP sometimes uses one of the deprecated addresses to
initiate a new association. Since the deprecated addresses are no valid
addresses in my configuration, this fails.

For me it looks like the sysctl variable net.inet6.ip6.use_deprecated is
misinterpreted. The RFC

https://tools.ietf.org/html/rfc2462#section-5.5.4

says, if activated, use deprecated address in open associations, only. It seems
SCTP uses deprecated addresses even for new associations, if the variable is
activated. 

In https://svnweb.freebsd.org/base/head/sys/netinet/sctp_bsd_addr.c starting
from line 126 a interface address gets marked as SCTP_ADDR_IFA_UNUSEABLE only,
if ip6_use_deprecated is false (which is basically
net.inet6.ip6.use_deprecated) and the interface address is marked as
IN6_IFF_DEPRECATED. Maybe this is the right position to start fixing this
issue.

Thanks,

Timo

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