CVE-2025-21655: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period

Severity: medium (CVSS 4.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-01-20 · updated 2026-10-15
Weakness: CWE-416

Description

In the Linux kernel, the following vulnerability has been resolved: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period io_eventfd_do_signal() is invoked from an RCU callback, but when dropping the reference to the io_ev_fd, it calls io_eventfd_free() directly if the refcount drops to zero. This isn't correct, as any potential freeing of the io_ev_fd should be deferred another RCU grace period. Just call io_eventfd_put() rather than open-code the dec-and-test and free, which will correctly defer it another RCU grace period.

Affected products

Linux kernel: from 6.1 before 6.1.125; from 6.2 before 6.6.72; from 6.7 before 6.12.10; 6.13-rc1, 6.13-rc2, 6.13-rc3, 6.13-rc4, 6.13-rc5, 6.13-rc6 — fixed in 6.1.125, 6.12.10, 6.6.72

How to fix

Upgrade to a fixed version: Linux kernel 6.1.125, 6.12.10, 6.6.72. Check the vendor advisory for mitigations.

References

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