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=============================================================================
FreeBSD-EN-19:15.libunwind                                      Errata Notice
                                                          The FreeBSD Project

Topic:          Incorrect exception handling

Category:       contrib
Module:         libunwind
Announced:      2019-08-06
Affects:        FreeBSD 11.2, FreeBSD 12.0
Corrected:      2019-08-06 17:08:30 UTC (releng/12.0, 12.0-RELEASE-p9)
                2019-08-06 17:08:30 UTC (releng/11.2, 11.2-RELEASE-p13)

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 libunwind library, which originates from the LLVM project, is responsible
for handling the unwinding of stack frames, when programs throw C or C++
style exceptions.  It uses exception handling information embedded in the
executable file to determine the layout of the stack, at the time the
exception is being processed.

II.  Problem Description

In some cases, the exception handling information embedded in executables is
not correctly interpreted by libunwind.  This causes it to emit a runtime
error, and abort the affected program.

III. Impact

Affected programs will show an message on the standard error stream, when
they attempt to throw an exception:

libunwind: getEncodedP \
 /usr/src/contrib/llvm/projects/libunwind/src/AddressSpace.hpp:280 - \
 unknown pointer encoding

After this message, the program will be aborted using the abort(3) function,
which usually results in a core dump.

IV.  Workaround

No workaround is available.

V.   Solution

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

1) 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

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-19:15/libunwind.patch
# fetch https://security.FreeBSD.org/patches/EN-19:15/libunwind.patch.asc
# gpg --verify libunwind.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
- -------------------------------------------------------------------------
releng/12.0/                                                      r350642
releng/11.2/                                                      r350642
- -------------------------------------------------------------------------

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=234201>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-19:15.libunwind.asc>
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