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FreeBSD-EN-19:07.lle                                            Errata Notice
                                                          The FreeBSD Project

Topic:          LLE table lookup code race condition

Category:       core
Module:         net
Announced:      2019-02-05
Credits:        Mark Johnston
Affects:        FreeBSD 12.0
Corrected:      2019-01-25 20:24:53 UTC (stable/12, 12.0-STABLE)
                2019-02-05 17:59:50 UTC (releng/12.0, 12.0-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:https://security.FreeBSD.org/>.

I.   Background

A LLE (link layer entry) table stores information about hosts on a network
and is used to translate between network layer addresses and data link layer
addresses.  The ARP cache, for example, is implemented using an LLE table.
LLEs typically expire after some period, so there exist mechanisms to
automatically remove them from their tables upon expiration.

II.  Problem Description

The LLE table lookup code for IPv4 and IPv6 contains a race which results in
a condition where the expiry period of an LLE is extended after it has been
removed from the table and freed.  By the time that the updated timer fires,
the LLE structure has been freed, and so the timer code is operating on freed
memory.

III. Impact

When the race is triggered, the result is typically a kernel panic.  It may
otherwise cause undefined system behavior.

IV.  Workaround

No workaround is available.

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 and reboot.

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
# shutdown -r +30 "Rebooting for errata update"

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.

# fetch https://security.FreeBSD.org/patches/EN-19:07/lle.patch
# fetch https://security.FreeBSD.org/patches/EN-19:07/lle.patch.asc
# gpg --verify lle.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
- -------------------------------------------------------------------------
stable/12/                                                        r343454
releng/12.0/                                                      r343787
- -------------------------------------------------------------------------

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

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=234296>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-19:07.lle.asc>
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