CVE-2025-21664High· 7.8▾ TwilightIn 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 …
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 42.9 · likelihood 0 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake.
Exploit-prediction probability, daily snapshots since Aug 1.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
0.2%
0.2% → 0.2%
Last analysed / modified upstream
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.
linux_kernel >= 3.15.1, < 5.4.290linux_kernel >= 5.5, < 5.10.234linux_kernel >= 5.11, < 5.15.177linux_kernel >= 5.16, < 6.1.125linux_kernel >= 6.2, < 6.6.72linux_kernel >= 6.7, < 6.12.10linux_kernel = 3.15linux_kernel = 6.13Upgrade past the affected range:
linux_kernel 6.12.10Connected by shared product, vendor, weakness, or advisory.
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