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============================================================================= FreeBSD-EN-18:09.ip Errata Notice
The FreeBSD Project

Topic: IP fragment remediation causes IPv6 fragment
reassembly failure

Category: core
Module: kernel
Announced: 2018-09-27
Credits: Kristof Provost
Affects: FreeBSD 11.1 and FreeBSD 11.2
Corrected: 2018-09-27 18:29:55 UTC (releng/11.2, 11.2-RELEASE-p4)
2018-09-27 18:29:55 UTC (releng/11.1, 11.1-RELEASE-p15)

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:https://security.FreeBSD.org/>.

I. Background

The recent security advisory titled SA-18:10.ip resolved an issue in the IPv4 and IPv6 fragment reassembly code.

II. Problem Description

As a result of fixing the issue describe in SA-18:10.ip, a regression was introduced in the IPv6 fragment hashing code which could cause reassembly to fail.

III. Impact

Received IPv6 packets requiring fragment reassembly may be dropped instead of properly reassembled and delivered.

IV. Workaround

Disable IPv6 fragment reassembly, using these commands:
% sysctl net.inet6.ip6.maxfrags=0

On systems compiled with VIMAGE, these sysctls will need to be
executed for each VNET.

V. Solution

Perform one of the following:

1) Upgrade your system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date.

Afterward, reboot the system.

2) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

Afterward, reboot the system.

3) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

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

[FreeBSD 11.x]
# fetch https://security.FreeBSD.org/patches/EN-18:09/ip.patch
# fetch https://security.FreeBSD.org/patches/EN-18:09/ip.patch.asc
# gpg --verify ip.patch.asc

b) Apply the patch. Execute the following commands as root:

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

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

VI. Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path Revision
- ------------------------------------------------------------------------- releng/11.1/ r338978 releng/11.2/ r338978
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

The security advisory that introduced the regression is available at <URL:https://www.freebsd.org/security/advisories/FreeBSD-SA-18:10.ip.asc>

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=231045>

The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-18:09.ip.asc> -----BEGIN PGP SIGNATURE-----

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