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FreeBSD-EN-26:19.zfs                                            Errata Notice
                                                          The FreeBSD Project

Topic:          Race conditions in zvol device management

Category:       contrib
Module:         openzfs
Announced:      2026-07-29
Affects:        FreeBSD 15.1 and 15.0
Corrected:      2026-07-27 17:33:34 UTC (stable/15, 15.1-STABLE)
                2026-07-29 17:50:28 UTC (releng/15.1, 15.1-RELEASE-p2)
                2026-07-29 17:50:04 UTC (releng/15.0, 15.0-RELEASE-p12)

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 an advanced and scalable file system originally developed by Sun
Microsystems for its Solaris operating system.  ZFS was integrated as part of
FreeBSD starting with FreeBSD 7.0.

ZFS volumes (zvols) are ZFS datasets that appear as block devices.  The
kernel creates and removes device nodes as zvols are created, destroyed, or
have their properties changed.

II.  Problem Description

Several race conditions existed in interactions between the zvol device
management code and FreeBSD's GEOM subsystem.

III. Impact

Operations on zvols such as renaming, changing properties, or destroying a
zvol while it is being opened can cause a kernel panic.

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, and reboot the system.

Perform one of the following:

1) To update your system installed from base system packages:

Systems running a 15.0-RELEASE or later version of FreeBSD on the amd64 or
arm64 platforms, which were installed using base system packages, can be
updated via the pkg(8) utility:

# pkg upgrade -r FreeBSD-base
# shutdown -r now

2) To update your system installed from binary distribution sets:

Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms
which were not installed using base system packages can be updated via the
freebsd-update(8) utility:

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

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-26:19/zfs.patch
# fetch https://security.FreeBSD.org/patches/EN-26:19/zfs.patch.asc
# gpg --verify zfs.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch -E -p0 < /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 in the
following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/15/                              698e0c419895    stable/15-n284603
releng/15.1/                            596030c13dce  releng/15.1-n283587
releng/15.0/                            4316500c27c6  releng/15.0-n281091
- -------------------------------------------------------------------------

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://github.com/openzfs/zfs/pull/18191>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-26:19.zfs.asc>
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