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FreeBSD-EN-16:18                                                Errata Notice
                                                          The FreeBSD Project

Topic:          Loader may hang during boot

Category:       core
Module:         loader
Announced:      2016-10-25
Affects:        FreeBSD 11.0
Corrected:      2016-10-08 00:01:07 UTC (stable/11, 11.0-STABLE)
                2016-10-25 16:50:10 UTC (releng/11.0, 11.0-RELEASE-p2)

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 the final stage (boot3) of the boot process and is responsible
for loading the kernel and starting the operating system.  GELIBoot is a
feature present in the loader that allows it to boot the system from an
encrypted disks.

II.  Problem Description

A programming error in GELIBoot causes the loader to attempt to read past
the end of the disk if the size of the final partition is not a multiple of
4 kB.

III. Impact

On most systems, reading past the end of the disk will result in the read
failing, and the boot process will continue normally.  On some systems, the
read past the end of the disk will be retried a number of times and will
result in the boot process being slower than usual.  On Amazon EC2 instances,
and possibly other virtualization platforms, this issue causes the boot
process to hang and never complete.

IV.  Workaround

No workaround is available, but systems with 4 kB aligned partitions will not
result in an attempt to read past the end of the disk.

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.

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

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 11.0]
# fetch https://security.FreeBSD.org/patches/EN-16:18/loader.patch
# fetch https://security.FreeBSD.org/patches/EN-16:18/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>.

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/11/                                                        r306834
releng/11.0/                                                      r307930
- -------------------------------------------------------------------------

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=213196>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-16:18.loader.asc>
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