[FreeBSD-Announce] FreeBSD Errata Notice FreeBSD-EN-21:21.ipfw

FreeBSD Errata Notices errata-notices at freebsd.org
Wed Jun 30 06:42:42 UTC 2021

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FreeBSD-EN-21:21.ipfw                                           Errata Notice
                                                          The FreeBSD Project

Topic:          Kernel panic with ipfw link-layer filtering enabled

Category:       core
Module:         ipfw
Announced:      2021-06-29
Affects:        FreeBSD 13.0
Corrected:      2021-06-19 14:08:49 UTC (stable/13, 13.0-STABLE)
                2021-06-29 17:09:43 UTC (releng/13.0, 13.0-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

I.   Background

ipfw(4) is a IP packet filter implementation in the kernel.  It uses the
pfil(9) interface to hook into several 

II.  Problem Description

When link-layer filtering is enabled by setting the net.link.ether.ipfw
sysctl to 1, packets received by the filter may be reallocated to ensure
that protocol headers are contiguous in memory.  In this case, the old
copy of the packet is freed.  However, the filter failed to update the
pointer returned to the pfil(9) caller, resulting in the use of a
pointer to freed memory.

III. Impact

Systems which use ipfw(4)'s link-layer filtering capabilities may panic.

IV.  Workaround

No workaround is available.  Systems not using ipfw(4), or systems that
do not explicitly enable link-layer filtering by setting the
net.link.ether.ipfw sysctl to 1, are not affected.

V.   Solution

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

Perform one of the following:

1) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64, i386, or
(on FreeBSD 13 and later) arm64 platforms can be updated via the
freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for an erratum update"

2) 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-21:21/ipfw.patch
# fetch https://security.FreeBSD.org/patches/EN-21:21/ipfw.patch.asc
# gpg --verify ipfw.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

VI.  Correction details

This issue is corrected by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/13/                              ed1acef3fe30    stable/13-n246063
releng/13.0/                            4647d115ff84  releng/13.0-n244750
- -------------------------------------------------------------------------

For FreeBSD 13 and later:

Run the following command to see which files were modified by a
particular commit:

# git show --stat <commit hash>

Or visit the following URL, replacing NNNNNN with the hash:


To determine the commit count in a working tree (for comparison against
nNNNNNN in the table above), run:

# git rev-list --count --first-parent HEAD

For FreeBSD 12 and earlier:

Run the following command to see which files were modified by a particular
revision, replacing NNNNNN with the revision number:

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

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


VII. References

<other info on the problem>


The latest revision of this advisory is available at


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