CVE-2025-38063
Medium · 5.5CVSS
5.5
EPSS
0.2%
Published
Jun 18, 2025
CISA due date
—
Cloudanix analysis
A kernel storage bug can make certain disk operations slower or pause unexpectedly on systems that use device mapper for storage.
- Exploitation
- Local Privilege
- Attacker needs
- Low Privilege
- Complexity
- Low
- Impact
- Denial Of Service
- Component
- OS kernel
- Class
- Other
- Remediation
- Upgrade
- Effort
- Medium
- Patch risk
- Low
What it actually does
The dm layer unconditionally applies wbt throttling to flush_bios generated by __send_empty_flush even when the original request (such as XFS metadata writes) is marked to bypass throttling.
Why it matters to the business
Systems using device-mapper with filesystems like XFS can experience unexpected IO stalls or reduced throughput on metadata operations, affecting database, log, and storage-heavy workloads until the kernel is updated.
How an attack unfolds
An attacker with local access can submit flush bios through a dm device to trigger wbt_wait on what should be unthrottled metadata IO, indirectly stalling filesystem operations; the listed threat actors appear unrelated to this specific throttling issue.
How to fix it
Upgrade the Linux kernel to a version containing commit 95d08924335f3b6f4ea0b92ebfe4fe0731c502d9 or later; apply the equivalent fix in any downstream distribution kernels that incorporate the change.
How to confirm the fix worked
Confirm the running kernel contains the referenced commit or a backport that adds REQ_IDLE to the flush_bio; test by submitting flush-heavy workloads and verifying that XFS log writes are no longer throttled.
Typical attack path
- Submit a bio with REQ_PREFLUSH to a dm device
- dm generates an internal flush_bio without REQ_IDLE
- wbt_should_throttle returns true and wbt_wait blocks the request
- XFS or similar metadata writers are stalled behind the throttle
How to detect it
Search kernel logs and block-layer traces for repeated wbt_wait calls on flush bios originating from dm; correlate with XFS CIL push or metadata write stalls.
What your security team should do
- Prioritize kernel updates on systems using dm with XFS or similar filesystems
- Monitor for IO latency spikes on affected hosts until patched
- Review device-mapper configurations for unnecessary flush traffic
The record
In the Linux kernel, the following vulnerability has been resolved: dm: fix unconditional IO throttle caused by REQ_PREFLUSH When a bio with REQ_PREFLUSH is submitted to dm, __send_empty_flush() generates a flush_bio with REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC, which causes the flush_bio to be throttled by wbt_wait(). An example from v5.4, similar problem also exists in upstream: crash> bt 2091206 PID: 2091206 TASK: ffff2050df92a300 CPU: 109 COMMAND: "kworker/u260:0" #0 [ffff800084a2f7f0] __switch_to at ffff80004008aeb8 #1 [ffff800084a2f820] __schedule at ffff800040bfa0c4 #2 [ffff800084a2f880] schedule at ffff800040bfa4b4 #3 [ffff800084a2f8a0] io_schedule at ffff800040bfa9c4 #4 [ffff800084a2f8c0] rq_qos_wait at ffff8000405925bc #5 [ffff800084a2f940] wbt_wait at ffff8000405bb3a0 #6 [ffff800084a2f9a0] __rq_qos_throttle at ffff800040592254 #7 [ffff800084a2f9c0] blk_mq_make_request at ffff80004057cf38 #8 [ffff800084a2fa60] generic_make_request at ffff800040570138 #9 [ffff800084a2fae0] submit_bio at ffff8000405703b4 #10 [ffff800084a2fb50] xlog_write_iclog at ffff800001280834 [xfs] #11 [ffff800084a2fbb0] xlog_sync at ffff800001280c3c [xfs] #12 [ffff800084a2fbf0] xlog_state_release_iclog at ffff800001280df4 [xfs] #13 [ffff800084a2fc10] xlog_write at ffff80000128203c [xfs] #14 [ffff800084a2fcd0] xlog_cil_push at ffff8000012846dc [xfs] #15 [ffff800084a2fda0] xlog_cil_push_work at ffff800001284a2c [xfs] #16 [ffff800084a2fdb0] process_one_work at ffff800040111d08 #17 [ffff800084a2fe00] worker_thread at ffff8000401121cc #18 [ffff800084a2fe70] kthread at ffff800040118de4 After commit 2def2845cc33 ("xfs: don't allow log IO to be throttled"), the metadata submitted by xlog_write_iclog() should not be throttled. But due to the existence of the dm layer, throttling flush_bio indirectly causes the metadata bio to be throttled. Fix this by conditionally adding REQ_IDLE to flush_bio.bi_opf, which makes wbt_should_throttle() return false to avoid wbt_wait().
Affected packages
| Ecosystem | Package | Introduced | Fixed |
|---|---|---|---|
| Debian:11 | linux | 0 | No fix |
| Debian:12 | linux | 0 | No fix |
| Debian:13 | linux | 0 | 6.12.32-1 |
| Debian:14 | linux | 0 | 6.12.32-1 |
| Linux | Kernel | 0 | 6.1.141 |
| Linux | Kernel | 4.10.0 | 6.1.141 |
| SUSE:Linux Enterprise High Availability Extension 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-livepatch-SLE15-SP6-RT_Update_14 | 0 | 1-150600.1.5.1 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-livepatch-SLE15-SP6_Update_14 | 0 | 1-150600.13.3.4 |
| SUSE:Linux Enterprise Live Patching 15 SP7 | kernel-livepatch-SLE15-SP7-RT_Update_3 | 0 | 1-150700.1.5.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-64kb | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-default-base | 0 | 6.4.0-150600.23.65.1.150600.12.28.4 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-source | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-zfcpdump | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-coco | 0 | 6.4.0-15061.28.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-coco_debug | 0 | 6.4.0-15061.28.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-source-coco | 0 | 6.4.0-15061.28.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-syms-coco | 0 | 6.4.0-15061.28.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-docs | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-obs-build | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-source | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-syms | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Module for Legacy 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-azure | 0 | 6.4.0-150600.8.48.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-source-azure | 0 | 6.4.0-150600.8.48.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-syms-azure | 0 | 6.4.0-150600.8.48.1 |
| SUSE:Linux Enterprise Workstation Extension 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.65.1 |
| SUSE:Real Time Module 15 SP6 | kernel-rt | 0 | 6.4.0-150600.10.49.1 |
| SUSE:Real Time Module 15 SP6 | kernel-rt_debug | 0 | 6.4.0-150600.10.49.1 |
| SUSE:Real Time Module 15 SP6 | kernel-source-rt | 0 | 6.4.0-150600.10.49.1 |
| SUSE:Real Time Module 15 SP6 | kernel-syms-rt | 0 | 6.4.0-150600.10.49.1 |
| SUSE:Real Time Module 15 SP7 | kernel-rt | 0 | 6.4.0-150700.7.13.1 |
| SUSE:Real Time Module 15 SP7 | kernel-source-rt | 0 | 6.4.0-150700.7.13.1 |
| SUSE:Real Time Module 15 SP7 | kernel-syms-rt | 0 | 6.4.0-150700.7.13.1 |
| openSUSE:Leap 15.6 | dtb-aarch64 | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-64kb | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-azure | 0 | 6.4.0-150600.8.48.1 |
| openSUSE:Leap 15.6 | kernel-debug | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-default | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-default-base | 0 | 6.4.0-150600.23.65.1.150600.12.28.4 |
| openSUSE:Leap 15.6 | kernel-docs | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-kvmsmall | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-obs-build | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-obs-qa | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-rt | 0 | 6.4.0-150600.10.49.1 |
| openSUSE:Leap 15.6 | kernel-rt_debug | 0 | 6.4.0-150600.10.49.1 |
| openSUSE:Leap 15.6 | kernel-source | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-source-azure | 0 | 6.4.0-150600.8.48.1 |
| openSUSE:Leap 15.6 | kernel-source-rt | 0 | 6.4.0-150600.10.49.1 |
| openSUSE:Leap 15.6 | kernel-syms | 0 | 6.4.0-150600.23.65.1 |
| openSUSE:Leap 15.6 | kernel-syms-azure | 0 | 6.4.0-150600.8.48.1 |
| openSUSE:Leap 15.6 | kernel-syms-rt | 0 | 6.4.0-150600.10.49.1 |
| openSUSE:Leap 15.6 | kernel-zfcpdump | 0 | 6.4.0-150600.23.65.1 |
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