CVE-2022-50549
Description
An ABBA deadlock flaw was found in the Linux kernel's device-mapper thin provisioning subsystem between the memory reclaim path and metadata abort handling. A local user can trigger this issue by initiating cache drop operations while dm-thin operations are active, causing process P1 to hold shrinker_rwsem and wait for pmd->root_lock while process P2 holds pmd->root_lock and waits for shrinker_rwsem during metadata abort. This results in a deadlock manifesting as hung tasks and system unresponsiveness, leading to denial of service.
Statement
The deadlock occurs through a specific interaction between memory management and device-mapper operations. When cache is dropped (via /proc/sys/vm/drop_caches), the shrink_slab path acquires shrinker_rwsem for reading, then processes filesystem operations that may involve dm-thin devices. Concurrently, when dm-thin metadata operations fail, the dm_pool_abort_metadata function acquires pmd->root_lock, destroys the block manager (which unregisters a shrinker), and attempts to acquire shrinker_rwsem for writing. Meanwhile, thin_map operations acquire pmd->root_lock for reading. This creates an ABBA deadlock: P1 holds shrinker_rwsem→waits for pmd->root_lock, P2 holds pmd->root_lock→waits for shrinker_rwsem.
Mitigation
To mitigate this issue, prevent the dm_thin_pool module from being loaded. See https://access.redhat.com/solutions/41278 for instructions on blacklisting kernel modules.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.5 | 5.5 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Other); DoS: Crash, Exit, or Restart
Each thread of execution will "hang" and prevent tasks from completing. In some cases, CPU consumption may occur if a lock check occurs in a tight loop.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
