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CVE-2025-21664

dm thin: make get_first_thin use rcu-safe list first function

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.4.290, 5.10.234, 5.15.177, 6.1.125, 6.6.72, and 1 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

Summary

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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From b10ebd34cccae1b431caf1be54919aede2be7cbe · fixed in ec037fe8c0d0f6140e3d8a49c7b29cb5582160b8; From b10ebd34cccae1b431caf1be54919aede2be7cbe · fixed in cd30a3960433ec2db94b3689752fa3c5df44d649; From b10ebd34cccae1b431caf1be54919aede2be7cbe · fixed in 802666a40c71a23542c43a3f87e3a2d0f4e8fe45; From b10ebd34cccae1b431caf1be54919aede2be7cbe · fixed in 12771050b6d059eea096993bf2001da9da9fddff; From b10ebd34cccae1b431caf1be54919aede2be7cbe · fixed in 6b305e98de0d225ccebfb225730a9f560d28ecb0; From b10ebd34cccae1b431caf1be54919aede2be7cbe · fixed in cbd0d5ecfa390ac29c5380200147d09c381b2ac6; From b10ebd34cccae1b431caf1be54919aede2be7cbe · fixed in 80f130bfad1dab93b95683fc39b87235682b8f72

  • Linux Linux

    3.15

  • KernelLinux

    From 3.15.0 · fixed in 5.4.290; From 5.5.0 · fixed in 5.10.234; From 5.11.0 · fixed in 5.15.177; From 5.16.0 · fixed in 6.1.125; From 6.2.0 · fixed in 6.6.72; From 6.7.0 · fixed in 6.12.10

References 7

git.kernel.org