CVE-2025-68807
block: fix race between wbt_enable_default and IO submission
Description
In the Linux kernel, the following vulnerability has been resolved: block: fix race between wbt_enable_default and IO submission When wbt_enable_default() is moved out of queue freezing in elevator_change(), it can cause the wbt inflight counter to become negative (-1), leading to hung tasks in the writeback path. Tasks get stuck in wbt_wait() because the counter is in an inconsistent state. The issue occurs because wbt_enable_default() could race with IO submission, allowing the counter to be decremented before proper initialization. This manifests as: rq_wait[0]: inflight: -1 has_waiters: True rwb_enabled() checks the state, which can be updated exactly between wbt_wait() (rq_qos_throttle()) and wbt_track()(rq_qos_track()), then the inflight counter will become negative. And results in hung task warnings like: task:kworker/u24:39 state:D stack:0 pid:14767 Call Trace: rq_qos_wait+0xb4/0x150 wbt_wait+0xa9/0x100 __rq_qos_throttle+0x24/0x40 blk_mq_submit_bio+0x672/0x7b0 ... Fix this by: 1. Splitting wbt_enable_default() into: - __wbt_enable_default(): Returns true if wbt_init() should be called - wbt_enable_default(): Wrapper for existing callers (no init) - wbt_init_enable_default(): New function that checks and inits WBT 2. Using wbt_init_enable_default() in blk_register_queue() to ensure proper initialization during queue registration 3. Move wbt_init() out of wbt_enable_default() which is only for enabling disabled wbt from bfq and iocost, and wbt_init() isn't needed. Then the original lock warning can be avoided. 4. Removing the ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT flag and its handling code since it's no longer needed This ensures WBT is properly initialized before any IO can be submitted, preventing the counter from going negative.
INFO
Published Date :
Jan. 13, 2026, 4:16 p.m.
Last Modified :
Jan. 13, 2026, 4:16 p.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Solution
- Update the Linux kernel to the patched version.
- Ensure WBT is properly initialized before IO submission.
- Apply code changes to prevent negative inflight counter.
- Remove outdated flags and handling code.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2025-68807.
| URL | Resource |
|---|---|
| https://git.kernel.org/stable/c/9869d3a6fed381f3b98404e26e1afc75d680cbf9 | |
| https://git.kernel.org/stable/c/f55201fb3becff6a903fd29f4d1147cc7e91eb0c |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2025-68807 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2025-68807
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2025-68807 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2025-68807 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jan. 13, 2026
Action Type Old Value New Value Added Description In the Linux kernel, the following vulnerability has been resolved: block: fix race between wbt_enable_default and IO submission When wbt_enable_default() is moved out of queue freezing in elevator_change(), it can cause the wbt inflight counter to become negative (-1), leading to hung tasks in the writeback path. Tasks get stuck in wbt_wait() because the counter is in an inconsistent state. The issue occurs because wbt_enable_default() could race with IO submission, allowing the counter to be decremented before proper initialization. This manifests as: rq_wait[0]: inflight: -1 has_waiters: True rwb_enabled() checks the state, which can be updated exactly between wbt_wait() (rq_qos_throttle()) and wbt_track()(rq_qos_track()), then the inflight counter will become negative. And results in hung task warnings like: task:kworker/u24:39 state:D stack:0 pid:14767 Call Trace: rq_qos_wait+0xb4/0x150 wbt_wait+0xa9/0x100 __rq_qos_throttle+0x24/0x40 blk_mq_submit_bio+0x672/0x7b0 ... Fix this by: 1. Splitting wbt_enable_default() into: - __wbt_enable_default(): Returns true if wbt_init() should be called - wbt_enable_default(): Wrapper for existing callers (no init) - wbt_init_enable_default(): New function that checks and inits WBT 2. Using wbt_init_enable_default() in blk_register_queue() to ensure proper initialization during queue registration 3. Move wbt_init() out of wbt_enable_default() which is only for enabling disabled wbt from bfq and iocost, and wbt_init() isn't needed. Then the original lock warning can be avoided. 4. Removing the ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT flag and its handling code since it's no longer needed This ensures WBT is properly initialized before any IO can be submitted, preventing the counter from going negative. Added Reference https://git.kernel.org/stable/c/9869d3a6fed381f3b98404e26e1afc75d680cbf9 Added Reference https://git.kernel.org/stable/c/f55201fb3becff6a903fd29f4d1147cc7e91eb0c