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FreeBSD-EN-20:05.mlx5en                                         Errata Notice
                                                          The FreeBSD Project

Topic:          Fix packet forwarding performance in mlx5en(4) driver

Category:       core
Module:         mlx5en
Announced:      2020-03-19
Affects:        FreeBSD 12.1
Corrected:      2019-11-07 13:12:38 UTC (stable/12, 12.1-STABLE)
                2020-03-19 16:41:29 UTC (releng/12.1, 12.1-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

Add CSUM_SND_TAG flag and set this flag for outgoing ratelimited mbufs.
This fixes an issue that redirected packets are dropped in the mlx5en
transmit routine.

II.  Problem Description

Ratelimiting support in the network stack reuses an mbuf field for a
different purpose to avoid having to grow the mbuf size.  This can a cause
packet drop in the forwarding case if the field in question is not cleared
prior to transmit.

III. Impact

All packets going through firewall code are dropped when using mlx5en(4).

IV.  Workaround

No workaround is available.  Systems not using mlx5en(4) are not affected.

V.   Solution

Perform one of the following:

1) 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

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.

[FreeBSD 12.1]
# fetch https://security.FreeBSD.org/patches/EN-20:05/mlx5en.patch
# fetch https://security.FreeBSD.org/patches/EN-20:05/mlx5en.patch.asc
# gpg --verify mlx5en.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/                                                        r354440
releng/12.1/                                                      r359136
- -------------------------------------------------------------------------

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=243871>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-20:05.mlx5en.asc>
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