Bug 2429069 (CVE-2025-68807)
| Summary: | CVE-2025-68807 kernel: block: fix race between wbt_enable_default and IO submission | ||
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| Product: | [Other] Security Response | Reporter: | OSIDB Bzimport <bzimport> |
| Component: | vulnerability | Assignee: | Product Security DevOps Team <prodsec-dev> |
| Status: | NEW --- | QA Contact: | |
| Severity: | low | Docs Contact: | |
| Priority: | low | ||
| Version: | unspecified | Keywords: | Security |
| Target Milestone: | --- | ||
| Target Release: | --- | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | --- | |
| Doc Text: |
A race condition flaw was found in the Linux kernel's block layer writeback throttling (WBT) initialization. When enabling WBT during an I/O elevator change, a race with concurrent I/O submission can cause the WBT inflight counter to become negative. This leads to tasks hanging indefinitely in wbt_wait(), resulting in system unresponsiveness.
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | Type: | --- | |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
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.