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:
- 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
- Using wbt_init_enable_default() in blk_register_queue() to ensure
proper initialization during queue registration
- 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.
- 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.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
- EG Severity
- Not assessed: no CVSS publishedA missing CVSS is not a severity of zero.
- EG Likelihood
- 0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-26). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- No SSVC decision: EchelonGraph has not assessed this CVECISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the BOD 26-04 block below.
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it