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FreeBSD-EN-19:02.tcp                                            Errata Notice
                                                          The FreeBSD Project

Topic:          TCP connections may stall and eventually fail in case of
                packet loss

Category:       core
Module:         kernel
Announced:      2019-01-09
Credits:        Michael Tuexen
Affects:        FreeBSD 12.0
Corrected:      2018-12-23 09:48:36 UTC (stable/12, 12.0-STABLE)
                2019-09-09 18:42:40 UTC (releng/12.0, 12.0-RELEASE-p2)

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 TCP stack limits the resources used for TCP connections.  Once a limit
is reached, further received TCP segments for the TCP connection are dropped.

II.  Problem Description

To continue delivering data to the application, accepting the TCP segment
with the next expected sequence number is required.  If this TCP segment is
dropped due to a resource limit, no further progress can be made. Therefore
exceptions for this particular TCP segment have to be implemented.

III. Impact

In case of lost TCP segments, TCP connections may stall and then eventually
fail.

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 12.0]
# fetch https://security.FreeBSD.org/patches/EN-19:02/tcp.patch
# fetch https://security.FreeBSD.org/patches/EN-19:02/tcp.patch.asc
# gpg --verify tcp.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/                                                        r342378
releng/12.0/                                                      r342894
- -------------------------------------------------------------------------

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

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-19:02.tcp.asc>
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