CVE-2021-46921

Name of the Vulnerable Software and Affected Versions Linux kernel (affected versions not specified)

Description The issue is related to the locking mechanism in the Linux kernel, specifically in the queued write lock slowpath() function. A reader can acquire the lock without holding the wait lock, allowing reads to observe values speculatively before the write lock is truly acquired. This exposes a window to an A-B-A problem, where a value change can be seen by the writer before the reader unlocks. The problem has been observed in epoll, where the reader does a xchg while holding the read lock, but the writer can see a value change out from under it. The atomic cond read acquire() and atomic cmpxchg relaxed() functions are involved in this issue. Switching the cmpxchg to use acquire semantics addresses this issue.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.