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

btrfs: reserve enough transaction items for qgroup ioctls

Currently our qgroup ioctls don't reserve any space, they just do a
transaction join, which does not reserve any space, neither for the quota
tree updates nor for the delayed refs generated when updating the quota
tree. The quota root uses the global block reserve, which is fine most of
the time since we don't expect a lot of updates to the quota root, or to
be too close to -ENOSPC such that other critical metadata updates need to
resort to the global reserve.

However this is not optimal, as not reserving proper space may result in a
transaction abort due to not reserving space for delayed refs and then
abusing the use of the global block reserve.

For example, the following reproducer (which is unlikely to model any
real world use case, but just to illustrate the problem), triggers such a
transaction abort due to -ENOSPC when running delayed refs:

$ cat test.sh
#!/bin/bash

DEV=/dev/nullb0
MNT=/mnt/nullb0

umount $DEV &> /dev/null
# Limit device to 1G so that it's much faster to reproduce the issue.
mkfs.btrfs -f -b 1G $DEV
mount -o commit=600 $DEV $MNT

fallocate -l 800M $MNT/filler
btrfs quota enable $MNT

for ((i = 1; i <= 400000; i++)); do
btrfs qgroup create 1/$i $MNT
done

umount $MNT

When running this, we can see in dmesg/syslog that a transaction abort
happened:

[436.490] BTRFS error (device nullb0): failed to run delayed ref for logical 30408704 num_bytes 16384 type 176 action 1 ref_mod 1: -28
[436.493] ------------[ cut here ]------------
[436.494] BTRFS: Transaction aborted (error -28)
[436.495] WARNING: fs/btrfs/extent-tree.c:2247 at btrfs_run_delayed_refs+0xd9/0x110 [btrfs], CPU#4: umount/2495372
[436.497] Modules linked in: btrfs loop (...)
[436.508] CPU: 4 UID: 0 PID: 2495372 Comm: umount Tainted: G W 6.19.0-rc8-btrfs-next-225+ #1 PREEMPT(full)
[436.510] Tainted: [W]=WARN
[436.511] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014
[436.513] RIP: 0010:btrfs_run_delayed_refs+0xdf/0x110 [btrfs]
[436.514] Code: 0f 82 ea (...)
[436.518] RSP: 0018:ffffd511850b7d78 EFLAGS: 00010292
[436.519] RAX: 00000000ffffffe4 RBX: ffff8f120dad37e0 RCX: 0000000002040001
[436.520] RDX: 0000000000000002 RSI: 00000000ffffffe4 RDI: ffffffffc090fd80
[436.522] RBP: 0000000000000000 R08: 0000000000000001 R09: ffffffffc04d1867
[436.523] R10: ffff8f18dc1fffa8 R11: 0000000000000003 R12: ffff8f173aa89400
[436.524] R13: 0000000000000000 R14: ffff8f173aa89400 R15: 0000000000000000
[436.526] FS: 00007fe59045d840(0000) GS:ffff8f192e22e000(0000) knlGS:0000000000000000
[436.527] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[436.528] CR2: 00007fe5905ff2b0 CR3: 000000060710a002 CR4: 0000000000370ef0
[436.530] Call Trace:
[436.530] <TASK>
[436.530] btrfs_commit_transaction+0x73/0xc00 [btrfs]
[436.531] ? btrfs_attach_transaction_barrier+0x1e/0x70 [btrfs]
[436.532] sync_filesystem+0x7a/0x90
[436.533] generic_shutdown_super+0x28/0x180
[436.533] kill_anon_super+0x12/0x40
[436.534] btrfs_kill_super+0x12/0x20 [btrfs]
[436.534] deactivate_locked_super+0x2f/0xb0
[436.534] cleanup_mnt+0xea/0x180
[436.535] task_work_run+0x58/0xa0
[436.535] exit_to_user_mode_loop+0xed/0x480
[436.536] ? __x64_sys_umount+0x68/0x80
[436.536] do_syscall_64+0x2a5/0xf20
[436.537] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[436.537] RIP: 0033:0x7fe5906b6217
[436.538] Code: 0d 00 f7 (...)
[436.540] RSP: 002b:00007ffcd87a61f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
[436.541] RAX: 0000000000000000 RBX: 00005618b9ecadc8 RCX: 00007fe5906b6217
[436.541] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00005618b9ecb100
[436.542] RBP: 0000000000000000 R08: 00007ffcd87a4fe0 R09: 00000000ffffffff
[436.544] R10: 0000000000000103 R11:
---truncated---
Published: 2026-05-08
Score: n/a
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

The bug occurs when qgroup ioctl calls in the BTRFS filesystem do not reserve sufficient transaction items; as a result, the kernel may fail to reserve space for delayed references and quota tree updates, causing a transaction abort with an -ENOSPC error. This can lead to a failure of file system operations and, in worst cases, corruption of BTRFS metadata if the abort is not handled correctly. The vulnerability does not provide a direct remote code execution path, but it can be abused to disrupt file system availability and stability.

Affected Systems

All Linux kernels that include BTRFS support are affected, regardless of distribution, until the fix is applied. The issue was observed in kernel 6.19.0-rc8 and earlier. No specific vendor or product versions are enumerated in the data, so any kernel version prior to the patch that contains BTRFS is potentially impacted.

Risk and Exploitability

The primary risk is a denial of service that can be triggered by privileged or local users performing heavy quota and qgroup operations on a BTRFS volume. The vulnerability lacks measurable web‑based exploitation potential; EPSS data is not available, and the issue is not listed in CISA’s KEV catalog. Because the flaw is tied to internal kernel bookkeeping, an attacker would need local or elevated privileges to exercise the affected ioctl path. The correct mitigations are to upgrade the kernel, or as a stop‑gap, avoid the qgroup feature or keep the filesystem sufficiently empty to avoid triggering the abort.

Generated by OpenCVE AI on May 8, 2026 at 18:30 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Apply the latest stable Linux kernel release that incorporates the BTRFS transaction reservation fix, or an actively maintained mainline kernel that includes the change.
  • If an update is not immediately possible, consider disabling BTRFS quotas or avoiding heavy qgroup manipulation on the affected volumes to reduce the likelihood of a transaction abort.
  • Regularly check system logs (e.g., dmesg, syslog) for BTRFS transaction abort messages and proactively keep enough free space to avoid reaching the –ENOSPC condition.

Generated by OpenCVE AI on May 8, 2026 at 18:30 UTC.

Tracking

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Advisories

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History

Fri, 08 May 2026 19:00:00 +0000

Type Values Removed Values Added
Weaknesses CWE-131

Fri, 08 May 2026 14:00:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: btrfs: reserve enough transaction items for qgroup ioctls Currently our qgroup ioctls don't reserve any space, they just do a transaction join, which does not reserve any space, neither for the quota tree updates nor for the delayed refs generated when updating the quota tree. The quota root uses the global block reserve, which is fine most of the time since we don't expect a lot of updates to the quota root, or to be too close to -ENOSPC such that other critical metadata updates need to resort to the global reserve. However this is not optimal, as not reserving proper space may result in a transaction abort due to not reserving space for delayed refs and then abusing the use of the global block reserve. For example, the following reproducer (which is unlikely to model any real world use case, but just to illustrate the problem), triggers such a transaction abort due to -ENOSPC when running delayed refs: $ cat test.sh #!/bin/bash DEV=/dev/nullb0 MNT=/mnt/nullb0 umount $DEV &> /dev/null # Limit device to 1G so that it's much faster to reproduce the issue. mkfs.btrfs -f -b 1G $DEV mount -o commit=600 $DEV $MNT fallocate -l 800M $MNT/filler btrfs quota enable $MNT for ((i = 1; i <= 400000; i++)); do btrfs qgroup create 1/$i $MNT done umount $MNT When running this, we can see in dmesg/syslog that a transaction abort happened: [436.490] BTRFS error (device nullb0): failed to run delayed ref for logical 30408704 num_bytes 16384 type 176 action 1 ref_mod 1: -28 [436.493] ------------[ cut here ]------------ [436.494] BTRFS: Transaction aborted (error -28) [436.495] WARNING: fs/btrfs/extent-tree.c:2247 at btrfs_run_delayed_refs+0xd9/0x110 [btrfs], CPU#4: umount/2495372 [436.497] Modules linked in: btrfs loop (...) [436.508] CPU: 4 UID: 0 PID: 2495372 Comm: umount Tainted: G W 6.19.0-rc8-btrfs-next-225+ #1 PREEMPT(full) [436.510] Tainted: [W]=WARN [436.511] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014 [436.513] RIP: 0010:btrfs_run_delayed_refs+0xdf/0x110 [btrfs] [436.514] Code: 0f 82 ea (...) [436.518] RSP: 0018:ffffd511850b7d78 EFLAGS: 00010292 [436.519] RAX: 00000000ffffffe4 RBX: ffff8f120dad37e0 RCX: 0000000002040001 [436.520] RDX: 0000000000000002 RSI: 00000000ffffffe4 RDI: ffffffffc090fd80 [436.522] RBP: 0000000000000000 R08: 0000000000000001 R09: ffffffffc04d1867 [436.523] R10: ffff8f18dc1fffa8 R11: 0000000000000003 R12: ffff8f173aa89400 [436.524] R13: 0000000000000000 R14: ffff8f173aa89400 R15: 0000000000000000 [436.526] FS: 00007fe59045d840(0000) GS:ffff8f192e22e000(0000) knlGS:0000000000000000 [436.527] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [436.528] CR2: 00007fe5905ff2b0 CR3: 000000060710a002 CR4: 0000000000370ef0 [436.530] Call Trace: [436.530] <TASK> [436.530] btrfs_commit_transaction+0x73/0xc00 [btrfs] [436.531] ? btrfs_attach_transaction_barrier+0x1e/0x70 [btrfs] [436.532] sync_filesystem+0x7a/0x90 [436.533] generic_shutdown_super+0x28/0x180 [436.533] kill_anon_super+0x12/0x40 [436.534] btrfs_kill_super+0x12/0x20 [btrfs] [436.534] deactivate_locked_super+0x2f/0xb0 [436.534] cleanup_mnt+0xea/0x180 [436.535] task_work_run+0x58/0xa0 [436.535] exit_to_user_mode_loop+0xed/0x480 [436.536] ? __x64_sys_umount+0x68/0x80 [436.536] do_syscall_64+0x2a5/0xf20 [436.537] entry_SYSCALL_64_after_hwframe+0x76/0x7e [436.537] RIP: 0033:0x7fe5906b6217 [436.538] Code: 0d 00 f7 (...) [436.540] RSP: 002b:00007ffcd87a61f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6 [436.541] RAX: 0000000000000000 RBX: 00005618b9ecadc8 RCX: 00007fe5906b6217 [436.541] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00005618b9ecb100 [436.542] RBP: 0000000000000000 R08: 00007ffcd87a4fe0 R09: 00000000ffffffff [436.544] R10: 0000000000000103 R11: ---truncated---
Title btrfs: reserve enough transaction items for qgroup ioctls
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-05-09T04:10:38.625Z

Reserved: 2026-05-01T14:12:56.003Z

Link: CVE-2026-43338

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-05-08T14:16:43.630

Modified: 2026-05-08T14:16:43.630

Link: CVE-2026-43338

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-08T22:00:14Z

Weaknesses