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FreeBSD-EN-23:22.vfs                                            Errata Notice
                                                          The FreeBSD Project

Topic:          ZFS snapshot directories not accessible over NFS

Category:       core
Module:         vfs
Announced:      2023-12-05
Affects:        FreeBSD 14.0
Corrected:      2023-12-01 13:27:28 UTC (stable/14, 14.0-STABLE)
                2023-12-05 18:27:40 UTC (releng/14.0, 14.0-RELEASE-p2)
                2023-12-04 21:03:42 UTC (stable/13, 13.2-STABLE)

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

ZFS is one of several filesystems available on FreeBSD.  ZFS supports many
advanced features, including checksumming, transparent compression, and
snapshots.

Snapshots of a ZFS dataset can be accessed through a hidden directory,
.zfs/snapshots, located in the root of the mounted dataset.

II.  Problem Description

When a process attempts to access a snapshot under /<dataset>/.zfs/snapshot,
the snapshot is automounted.  However, without this patch, the automount does
not properly set some metadata in the kernel's representation of the mount
point, which results in the snapshot not being accessible over NFS.

III. Impact

Workflows which rely on ZFS snapshots being accessible over NFS are broken.

IV.  Workaround

No workaround is available.

V.   Solution

Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date.  A reboot is required after
the upgrade procedure has been completed.

Perform one of the following:

1) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms,
or the i386 platfrom on FreeBSD 13 and earlier, can be updated via
the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r now

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-23:22/vfs.patch
# fetch https://security.FreeBSD.org/patches/EN-23:22/vfs.patch.asc
# gpg --verify vfs.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 as of the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/14/                              62304a0c3b8b    stable/14-n265867
releng/14.0/                            889ecd8fd178  releng/14.0-n265394
stable/13/                              00f0b99e63c3    stable/13-n256835
- -------------------------------------------------------------------------

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

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275200>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-23:22.vfs.asc>
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