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FreeBSD-EN-18:10.syscall                                        Errata Notice
                                                          The FreeBSD Project

Topic:          NULL pointer dereference in freebsd4_getfsstat system call

Category:       core
Module:         kernel
Announced:      2018-09-27
Credits:        Thomas Barabosch, Fraunhofer FKIE
Affects:        FreeBSD 11.x
Corrected:      2018-09-27 18:54:41 UTC (stable/11, 11.1-STABLE)
                2018-09-27 18:32:14 UTC (releng/11.2, 11.2-RELEASE-p4)
                2018-09-27 18:32:14 UTC (releng/11.1, 11.1-RELEASE-p15)
CVE Name:       CVE-2018-17154

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 freebsd4_getfsstat system call returns information about all mounted file
systems in a binary format compatible with FreeBSD 4.x. Part of the call
includes passing in a userland allocated buffer for the system call to fill
along with the size of the buffer.

II.  Problem Description

Insufficient checking occurs on the buffer when a very large buffer size causes 
memory allocation to fail. Resulting code attempts to free the NULL pointer.

III. Impact

A local unprivileged user may cause a denial of service using a specially
crafted binary.

IV.  Workaround

No workaround is available.

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.x]
# fetch https://security.FreeBSD.org/patches/EN-18:10/syscall-11.patch
# fetch https://security.FreeBSD.org/patches/EN-18:10/syscall-11.patch.asc
# gpg --verify syscall-11.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/11/                                                        r338987
releng/11.1/                                                      r338979
releng/11.2/                                                      r338979
- -------------------------------------------------------------------------

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-2018-17154>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-18:10.syscall.asc>
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