In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix qgroup reserve overflow the qgroup limit

We use extent_changeset->bytes_changed in qgroup_reserve_data() to record
how many bytes we set for EXTENT_QGROUP_RESERVED state. Currently the
bytes_changed is set as "unsigned int", and it will overflow if we try to
fallocate a range larger than 4GiB. The result is we reserve less bytes
and eventually break the qgroup limit.

Unlike regular buffered/direct write, which we use one changeset for
each ordered extent, which can never be larger than 256M. For
fallocate, we use one changeset for the whole range, thus it no longer
respects the 256M per extent limit, and caused the problem.

The following example test script reproduces the problem:

$ cat qgroup-overflow.sh
#!/bin/bash

DEV=/dev/sdj
MNT=/mnt/sdj

mkfs.btrfs -f $DEV
mount $DEV $MNT

# Set qgroup limit to 2GiB.
btrfs quota enable $MNT
btrfs qgroup limit 2G $MNT

# Try to fallocate a 3GiB file. This should fail.
echo
echo "Try to fallocate a 3GiB file..."
fallocate -l 3G $MNT/3G.file

# Try to fallocate a 5GiB file.
echo
echo "Try to fallocate a 5GiB file..."
fallocate -l 5G $MNT/5G.file

# See we break the qgroup limit.
echo
sync
btrfs qgroup show -r $MNT

umount $MNT

When running the test:

$ ./qgroup-overflow.sh
(...)

Try to fallocate a 3GiB file...
fallocate: fallocate failed: Disk quota exceeded

Try to fallocate a 5GiB file...

qgroupid         rfer         excl     max_rfer
--------         ----         ----     --------
0/5           5.00GiB      5.00GiB      2.00GiB

Since we have no control of how bytes_changed is used, it's better to
set it to u64.
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Tue, 23 Sep 2025 18:45:00 +0000

Type Values Removed Values Added
Weaknesses CWE-190
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.18:rc1:*:*:*:*:*:*

Thu, 27 Feb 2025 01:45:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate


Wed, 26 Feb 2025 02:15:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: btrfs: fix qgroup reserve overflow the qgroup limit We use extent_changeset->bytes_changed in qgroup_reserve_data() to record how many bytes we set for EXTENT_QGROUP_RESERVED state. Currently the bytes_changed is set as "unsigned int", and it will overflow if we try to fallocate a range larger than 4GiB. The result is we reserve less bytes and eventually break the qgroup limit. Unlike regular buffered/direct write, which we use one changeset for each ordered extent, which can never be larger than 256M. For fallocate, we use one changeset for the whole range, thus it no longer respects the 256M per extent limit, and caused the problem. The following example test script reproduces the problem: $ cat qgroup-overflow.sh #!/bin/bash DEV=/dev/sdj MNT=/mnt/sdj mkfs.btrfs -f $DEV mount $DEV $MNT # Set qgroup limit to 2GiB. btrfs quota enable $MNT btrfs qgroup limit 2G $MNT # Try to fallocate a 3GiB file. This should fail. echo echo "Try to fallocate a 3GiB file..." fallocate -l 3G $MNT/3G.file # Try to fallocate a 5GiB file. echo echo "Try to fallocate a 5GiB file..." fallocate -l 5G $MNT/5G.file # See we break the qgroup limit. echo sync btrfs qgroup show -r $MNT umount $MNT When running the test: $ ./qgroup-overflow.sh (...) Try to fallocate a 3GiB file... fallocate: fallocate failed: Disk quota exceeded Try to fallocate a 5GiB file... qgroupid         rfer         excl     max_rfer --------         ----         ----     -------- 0/5           5.00GiB      5.00GiB      2.00GiB Since we have no control of how bytes_changed is used, it's better to set it to u64.
Title btrfs: fix qgroup reserve overflow the qgroup limit
References

cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2025-05-04T08:29:11.296Z

Reserved: 2025-02-26T01:49:39.245Z

Link: CVE-2022-49075

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Analyzed

Published: 2025-02-26T07:00:44.847

Modified: 2025-09-23T18:32:06.833

Link: CVE-2022-49075

cve-icon Redhat

Severity : Moderate

Publid Date: 2025-02-26T00:00:00Z

Links: CVE-2022-49075 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2025-07-12T15:42:40Z