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FreeBSD-EN-22:11.zfs                                            Errata Notice
                                                          The FreeBSD Project

Topic:          ZFS lseek(2) inconsistencies

Category:       contrib
Module:         zfs
Announced:      2022-03-15
Affects:        FreeBSD 13.0
Corrected:      2021-12-19 15:25:26 UTC (stable/13, 13.0-STABLE)
                2022-03-15 18:09:52 UTC (releng/13.0, 13.0-RELEASE-p8)

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.

File "holes" are used by filesystems to limit the amount of storage
space occupied by a file containing long runs of zero bytes.  Rather
than filling disk blocks with zeroes, file metadata can indicate the
extent of such a run and the filesystem hides the distinction from user
applications.

II.  Problem Description

When a file containing holes is mapped using mmap(2), mapped regions
of the file may be ignored by lseek(2) when SEEK_HOLE or SEEK_DATA are
passed as the "whence" parameter.

III. Impact

The bug may cause application misbehavior; the precise effects depend
on the nature of the application triggering the bug.

IV.  Workaround

No workaround is available, but systems not using ZFS are not affected.

V.   Solution

Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date and reboot.

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
# shutdown -r +10min "Rebooting for an errata update"

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-22:11/zfs.patch
# fetch https://security.FreeBSD.org/patches/EN-22:11/zfs.patch.asc
# gpg --verify zfs.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/                              3aa1cabca37d    stable/13-n248633
releng/13.0/                            f5be20afc356  releng/13.0-n244785
- -------------------------------------------------------------------------

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=256205>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-22:11.zfs.asc>
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