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FreeBSD-EN-16:05.hv_netvsc                                      Errata Notice
                                                          The FreeBSD Project

Topic:          hv_netvsc(4) incorrect TCP/IP checksums

Category:       core
Module:         hyperv
Announced:      2016-03-16
Credits:        Larry Baird
Affects:        FreeBSD 10.2
Corrected:      2015-12-18 14:56:49 UTC (stable/10, 10.2-STABLE)
                2016-03-16 22:31:04 UTC (releng/10.2, 10.2-RELEASE-p14)

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

Hyper-V is a native hypervisor running on Windows operating system. It can
run FreeBSD 10.x as guest in virtual machine.

When FreeBSD guest runs on Hyper-V, to get the best network performance,
it usually uses the Hyper-V synthetic network device.  The driver of the
network device is called hv_netvsc(4).  Since FreeBSD 10.2-RELEASE the
driver supports TCP segmentation and TCP/IP checksum offloading.

II.  Problem Description

Together with the TCP segmentation and TCP/IP checksum offloading a regression
was introduced.  The driver checked the inbound checksum flags when deciding
whether to process checksums or not, while it should have checked the outbound
flags only.

III. Impact

If the guest running on Hyper-V is configured as a gateway, the host will
silently drop certain packets from the guest.

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.  Reboot is required.

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

Reboot is required.

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.

# fetch https://security.FreeBSD.org/patches/EN-16:05/hv_netvsc.patch
# fetch https://security.FreeBSD.org/patches/EN-16:05/hv_netvsc.patch.asc
# gpg --verify hv_netvsc.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/                                                        r292439
releng/10.2/                                                      r296955
- -------------------------------------------------------------------------

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=203630>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-16:05.hv_netvsc.asc>
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