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FreeBSD-SA-19:17.fd Security Advisory
The FreeBSD Project

Topic: File description reference count leak

Category: core
Module: unix
Announced: 2019-07-24
Credits: Mark Johnston
Affects: All supported versions of FreeBSD.
Corrected: 2019-07-22 19:25:05 UTC (stable/12, 12.0-STABLE)
2019-07-24 12:57:49 UTC (releng/12.0, 12.0-RELEASE-p8)
2019-07-22 19:27:23 UTC (stable/11, 11.2-STABLE)
2019-07-24 12:57:49 UTC (releng/11.2, 11.2-RELEASE-p12)
2019-07-24 12:57:49 UTC (releng/11.3, 11.3-RELEASE-p1)
CVE Name: CVE-2019-5607

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I. Background

UNIX-domain sockets are used for inter-process communication. It is
possible to use UNIX-domain sockets to transfer rights, encoded as file
descriptors, to another process. Rights are encapsulated in control
messages, and multiple such messages may be transmitted with a single
system call.

II. Problem Description

If a process attempts to transmit rights over a UNIX-domain socket and
an error causes the attempt to fail, references acquired on the rights
are not released and are leaked. This bug can be used to cause the
reference counter to wrap around and free the corresponding file
structure.

III. Impact

A local user can exploit the bug to gain root privileges or escape from
a jail.

IV. Workaround

No workaround is available.

V. Solution

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

Perform one of the following:

1) To update your vulnerable 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 +10min “Rebooting for a security update”

2) To update your vulnerable 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/SA-19:17/fd.11.2.patch
# fetch https://security.FreeBSD.org/patches/SA-19:17/fd.11.2.patch.asc
# gpg –verify fd.11.2.patch.asc

[FreeBSD 11.3]
# fetch https://security.FreeBSD.org/patches/SA-19:17/fd.11.patch
# fetch https://security.FreeBSD.org/patches/SA-19:17/fd.11.patch.asc
# gpg –verify fd.11.patch.asc

[FreeBSD 12.0]
# fetch https://security.FreeBSD.org/patches/SA-19:17/fd.12.patch
# fetch https://security.FreeBSD.org/patches/SA-19:17/fd.12.patch.asc
# gpg –verify fd.12.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/ r350222
releng/12.0/ r350286
stable/11/ r350223
releng/11.2/ r350286
releng/11.3/ r350286
– ————————————————————————-

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://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-5607>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-19:17.fd.asc>
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