Re: FreeBSD Errata Notice FreeBSD-EN-22:25.tcp

Hi,

This fix an annoying issue I encountered when I updated one of my build box
from 12.3 to 13.1.

When remote copying large files from the build box to my local laptop (MBP),
sometimes the pipe broke and end up with 'lost connection'.

```
zlei@Zhenleis-MacBook-Pro:/tmp % scp xx.xx.xx.xx:~/stable12/kernel.txz ./
Enter passphrase for key '/Users/zlei/.ssh/id_rsa':
kernel.txz                                                                                                                                          38%   17MB   2.0MB/s   00:13 ETA
ssh_dispatch_run_fatal: Connection to xx.xx.xx.xx port 22: message authentication code incorrect
lost connection
```

Sometimes the ssh session to the build box interrupts, commonly  when there're
a lot of output from terminal. make buildkernel e.g.

Thanks for the fix!


Best regards,
Zhenlei

> On Nov 2, 2022, at 6:21 AM, FreeBSD Errata Notices <errata-notices@freebsd.org> wrote:
> 
> Signed PGP part
> =============================================================================
> FreeBSD-EN-22:25.tcp                                      Errata Notice
>                                                           The FreeBSD Project
> 
> Topic:          Possible data corruption with TCP SACK retransmissions
> 
> Category:       core
> Module:         tcp
> Announced:      2022-08-28
> Credits:	Richard Scheffenegger
> Affects:        FreeBSD 13.1
> Corrected:      2022-09-14 01:28:03 UTC (stable/13, 13.1-STABLE)
>                 2022-11-01 13:28:11 UTC (releng/13.1, 13.1-RELEASE-p3)
> 
> 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
> 
> TCP supports an enhancement that allows faster recovery and retransmission of
> data when loss is discovered called Selected Acknowledgements (SACK).
> 
> SACK allows a TCP sender to communicate more information about which segments
> are lost. During a SACK episode a TCP sender will reduce its rate to avoid
> causing congestion on the network.
> 
> II.  Problem Description
> 
> A change made to make TCP more resilient and effective when handling loss
> recovery by SACK, could lead to connection interruption when incoming ACKs
> suddenly no longer contain SACK blocks.
> 
> III. Impact
> 
> This can lead to correct data being placed at the wrong offset in the
> stream in a non-deterministic manner. This can result in termination of
> the TCP connection by the application or in the worst case silent data
> corruption.
> 
> IV.  Workaround
> 
> Disable SACK globally by setting the net.inet.tcp.sack.enable sysctl to 0:
> 
>     # sysctl net.inet.tcp.sack.enable=0
> 
> Note that this will only affect new connections. Thus, either persist the
> setting in /etc/sysctl.conf and reboot, or ensure that any critical connections
> are restarted after modifying the sysctl setting.
> 
> V.   Solution
> 
> Upgrade your system to a supported FreeBSD stable or release / security
> branch (releng) dated after the correction date.
> 
> A reboot is required for these changes to be applied.
> 
> Perform one of the following:
> 
> 1) To update your system via a binary patch:
> 
> Systems running a RELEASE version of FreeBSD on the amd64, i386, or
> (on FreeBSD 13 and later) arm64 platforms can be updated via the
> freebsd-update(8) utility:
> 
> # freebsd-update fetch
> # freebsd-update install
> 
> A reboot is required for these changes to be applied.
> 
> 2) 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-22:25/tcp.patch
> # fetch https://security.FreeBSD.org/patches/EN-22:25/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
> 
> This issue is corrected by the corresponding Git commit hash or Subversion
> revision number in the following stable and release branches:
> 
> Branch/path                             Hash                     Revision
> -------------------------------------------------------------------------
> stable/13/                              2b8ee332b938  stable/13-n252399
> releng/13.1/                            dd35207e2025  releng/13.1-n250162
> -------------------------------------------------------------------------
> 
> Run the following command to see which files were modified by a
> particular commit:
> 
> # git show --stat <commit hash>
> 
> Or visit the following URL, replacing NNNNNN with the hash:
> 
> <URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>
> 
> To determine the commit count in a working tree (for comparison against
> nNNNNNN in the table above), run:
> 
> # git rev-list --count --first-parent HEAD
> 
> VII. References
> 
> The latest revision of this advisory is available at
> <URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-22:25.tcp.asc>
> 
>