CVE-20XX-?
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CVE-2025-21664

7.8 HIGH 0.2% exploit odds Fix listed Memory safety OS & kernel

What it is

In the Linux kernel, the following vulnerability has been resolved: dm thin: make get_first_thin use rcu-safe list first function The documentation in rculist.h explains the absence of list_empty_rcu() and cautions programmers against relying on a list_empty() -> list_first() sequence in RCU safe code. This is because each of these functions performs its own READ_ONCE() of the list head. This can lead to a situation where the list_empty() sees a valid list entry, but the subsequent list_first() sees a different view of list head state after a modification. In the case of dm-thin, this author had a production box crash from a GP fault in the process_deferred_bios path. This function saw a valid list head in get_first_thin() but when it subsequently dereferenced that and turned it into a thin_c, it got the inside of the struct pool, since the list was now empty and referring to itself. The kernel on which this occurred printed both a warning about a refcount_t being saturated, and a UBSAN error for an out-of-bounds cpuid access in the queued spinlock, prior to the fault itself. When the resulting kdump was examined, it was possible to see another thread patiently waiting in thin_dtr's synchronize_rcu. The thin_dtr call managed to pull the thin_c out of the active thins list (and have it be the last entry in the active_thins list) at just the wrong moment which lead to this crash. Fortunately, the fix here is straight forward. Switch get_first_thin() function to use list_first_or_null_rcu() which performs just a single READ_ONCE() and returns NULL if the list is already empty. This was run against the devicemapper test suite's thin-provisioning suites for delete and suspend and no regressions were observed.

At a glance

Exploitability
Can be exploited locally on the machine with a low-privilege account. High risk of data exposure, data tampering, service disruption.
Exploit odds
0.2% chance of exploitation in the next 30 days (EPSS).
Fix
A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

  1. PublishedDisclosed publicly on CVE.org and NVD
  2. Last updatedMost recent change to the record

Why it ranks here

Details

Published
Last modified
Exploit probability
0.2% · EPSS, next 30 days
Record status
Modified

Affected

Attack profile CVSS 3.1 · 7.8

Attack vector
Local
Complexity
Low
Privileges needed
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Raw vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Is it in your code?

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Fix and advisories

References

NVD record · CVE.org record