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FreeBSD-EN-18:15.loader                                         Errata Notice
                                                          The FreeBSD Project

Topic:          Deferred kernel loading breaks loader password

Category:       core
Module:         loader
Announced:      2018-11-27
Credits:        Devin Teske
Affects:        All supported versions of FreeBSD.
Corrected:      2018-10-24 23:17:17 UTC (stable/11, 11.2-STABLE)
                2018-11-27 19:45:25 UTC (releng/11.2, 11.2-RELEASE-p5)

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 loader is a FreeBSD component which is part of the boot sequence for a
machine. The loader is most commonly visible with the "beastie" boot menu,
allowing specification of different boot time parameters.

II.  Problem Description

A change in the loader to allow deferred loading of the kernel introduced a
bug when using a loader password.  After this change and when the loader
password is enabled, the menu is not loaded and instead the machine goes into
the autoboot routine.  The autoboot routine then fails when the kernel has
not yet been loaded, yielding a loader prompt where the user has full control
of the boot process. 

III. Impact

Setting the loader password with the intention of preventing the user from
bypassing the boot process instead causes the boot to fail and gives the user
full control of the boot process.

IV.  Workaround

No workaround is available, but systems that do not use a loader password are
not vulnerable.

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 11.2]
# fetch https://security.FreeBSD.org/patches/EN-18:15/loader.patch
# fetch https://security.FreeBSD.org/patches/EN-18:15/loader.patch.asc
# gpg --verify loader.patch.asc

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

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

c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html> and reboot
the system.

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/11/                                                        r339697
releng/11.2/                                                      r341093
- -------------------------------------------------------------------------

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 latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-18:15.loader.asc>
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