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FreeBSD-EN-12:02.ipv6refcount                                   Errata Notice
                                                          The FreeBSD Project

Topic:          Reference count errors in IPv6 code

Category:       core
Modules:        sys_netinet sys_netinet6
Announced:      2012-06-12
Credits:        Scott Long, Rui Paulo, Maksim Yevmenkin
Affects:        FreeBSD 8.0 and later
Corrected:      2012-06-09 22:44:49 UTC (RELENG_8, 8.3-STABLE)
                2012-06-12 12:10:10 UTC (RELENG_8_3, 8.3-RELEASE-p3)
                2012-06-12 12:10:10 UTC (RELENG_8_2, 8.2-RELEASE-p9)
                2012-06-12 12:10:10 UTC (RELENG_8_1, 8.1-RELEASE-p11)
                2012-06-09 22:44:24 UTC (RELENG_9, 9.0-STABLE)
                2012-06-12 12:10:10 UTC (RELENG_9_0, 9.0-RELEASE-p3)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:http://security.freebsd.org/>.

I.   Background

The FreeBSD network stack implements Internet Protocol version 6 (IPv6),
the successor to IPv4.  IPv6 is now seeing widespread deployment.

Reference counts are a programming technology used by the FreeBSD kernel
to maintain stability of objects while in use.

II.  Problem Description

The FreeBSD IPv4 and IPv6 kernel implementations employ reference counts to
protect IP addresses configured on network interfaces.  Due to multiple
bugs, IPv6 address references may be improperly acquired or released; IPv4
is unaffected.

III. Impact

Under high IPv6 network load, reference counts may improperly hit zero
due to overflow or underflow, causing an IPv6 address, which is still in
use, to be freed.  This will lead to a kernel panic on next access.

IV.  Workaround

No workaround is available, but systems not using any IPv6 communication
are not affected.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 8-STABLE, or 9-STABLE, or to the
RELENG_8_3, RELENG_8_2, RELENG_8_1, or RELENG_9_0 security branch dated
after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 8.3, 8.2,
8.1, and 9.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 8.1-RELEASE, 8.2-RELEASE, and 9.0-RELEASE]
# fetch http://security.FreeBSD.org/patches/EN-12:02/ipv6refcount.patch
# fetch http://security.FreeBSD.org/patches/EN-12:02/ipv6refcount.patch.asc

[FreeBSD 8.3-RELEASE]
# fetch http://security.FreeBSD.org/patches/EN-12:02/ipv6refcount-83.patch
# fetch http://security.FreeBSD.org/patches/EN-12:02/ipv6refcount-83.patch.asc

b) Apply the patch.

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:http://www.freebsd.org/handbook/kernelconfig.html> and reboot the
system.

3) To update your vulnerable system via a binary patch:

Systems running 8.3-RELEASE, 8.2-RELEASE, 8.1-RELEASE, or 9.0-RELEASE on
the i386 or amd64 platforms can be updated via the freebsd-update(8)
utility:

# freebsd-update fetch
# freebsd-update install

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

CVS:

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_8
  sys/netinet/tcp_input.c                                      1.411.2.22
  sys/netinet6/in6.c                                           1.121.2.28
  sys/netinet6/ip6_input.c                                      1.132.2.9
RELENG_8_3
  src/UPDATING                                             1.632.2.26.2.5
  src/sys/conf/newvers.sh                                   1.83.2.15.2.7
  sys/netinet/tcp_input.c                                  1.411.2.19.2.2
  sys/netinet6/in6.c                                       1.121.2.23.2.2
  sys/netinet6/ip6_input.c                                  1.132.2.6.4.2
RELENG_8_2
  src/UPDATING                                            1.632.2.19.2.11
  src/sys/conf/newvers.sh                                  1.83.2.12.2.14
  sys/netinet/tcp_input.c                                   1.411.2.9.2.2
  sys/netinet6/in6.c                                       1.121.2.12.2.2
  sys/netinet6/ip6_input.c                                  1.132.2.6.2.2
RELENG_8_1
  src/UPDATING                                            1.632.2.14.2.14
  src/sys/conf/newvers.sh                                  1.83.2.10.2.15
  sys/netinet/tcp_input.c                                   1.411.2.6.2.2
  sys/netinet6/in6.c                                       1.121.2.11.2.2
  sys/netinet6/ip6_input.c                                  1.132.2.4.2.2
RELENG_9
  sys/netinet/tcp_input.c                                       1.437.2.7
  sys/netinet6/in6.c                                           1.139.2.16
  sys/netinet6/ip6_input.c                                      1.147.2.4
RELENG_9_0
  src/UPDATING                                              1.702.2.4.2.5
  src/sys/conf/newvers.sh                                    1.95.2.4.2.7
  sys/netinet/tcp_input.c                                   1.437.2.2.2.2
  sys/netinet6/in6.c                                        1.139.2.4.2.2
  sys/netinet6/ip6_input.c                                  1.147.2.1.2.2
- -------------------------------------------------------------------------

Subversion:

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/8/                                                         r236827
releng/8.3/                                                       r236953
releng/8.2/                                                       r236953
releng/8.1/                                                       r236953
stable/9/                                                         r236826
releng/9.0/                                                       r236953
- -------------------------------------------------------------------------

VII. References

The latest revision of this Errata Notice is available at
http://security.FreeBSD.org/advisories/FreeBSD-EN-12:02.ipv6refcount.asc
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