Question: What is CVE-2025-21686?
Answer: CVE-2025-21686 is a vulnerability classified as nan with a CVSS score of nan. It falls under nan and affects the system as follows: In the Linux kernel, the following vulnerability has been resolved:

io_uring/rsrc: require cloned buffers to share accounting contexts

When IORING_REGISTER_CLONE_BUFFERS is used to clone buffers from uring
instance A to uring instance B, where A and B use different MMs for
accounting, the accounting can go wrong:
If uring instance A is closed before uring instance B, the pinned memory
counters for uring instance B will be decremented, even though the pinned
memory was originally accounted through uring instance A; so the MM of
uring instance B can end up with negative locked memory.