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FreeBSD-SA-16:19.sendmsg                                    Security Advisory
                                                          The FreeBSD Project

Topic:          Incorrect argument handling in sendmsg(2)

Category:       core
Module:         kernel
Announced:      2016-05-17
Credits:        CTurt and the HardenedBSD team
Affects:        FreeBSD 10.x
Corrected:      2016-05-17 22:30:43 UTC (stable/10, 10.3-STABLE)
                2016-05-17 22:28:27 UTC (releng/10.3, 10.3-RELEASE-p3)
                2016-05-17 22:28:20 UTC (releng/10.2, 10.2-RELEASE-p17)
                2016-05-17 22:28:11 UTC (releng/10.1, 10.1-RELEASE-p34)
CVE Name:       CVE-2016-1887

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

The sendmsg(2) system call allows to send data to a socket.  The data
may be accompanied by optional ancillary data.

II.  Problem Description

Incorrect argument handling in the socket code allows malicious local
user to overwrite large portion of the kernel memory.

III. Impact

Malicious local user may crash kernel or execute arbitrary code in the kernel,
potentially gaining superuser privileges.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

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

Reboot is required.

2) 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

Reboot is required.

3) 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.

# fetch https://security.FreeBSD.org/patches/SA-16:19/sendmsg.patch
# fetch https://security.FreeBSD.org/patches/SA-16:19/sendmsg.patch.asc
# gpg --verify sendmsg.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/10/                                                        r300092
releng/10.1/                                                      r300085
releng/10.2/                                                      r300086
releng/10.3/                                                      r300087
- -------------------------------------------------------------------------

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:http://cturt.github.io/sendmsg.html>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1887>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:19.sendmsg.asc>
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