CVE-2025-71070

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

ublk: clean up user copy references on ublk server exit

If a ublk server process releases a ublk char device file, any requests

dispatched to the ublk server but not yet completed will retain a ref

value of UBLK_REFCOUNT_INIT. Before commit e63d2228ef83 ("ublk: simplify

aborting ublk request"), __ublk_fail_req() would decrement the reference

count before completing the failed request. However, that commit

optimized __ublk_fail_req() to call __ublk_complete_rq() directly

without decrementing the request reference count.

The leaked reference count incorrectly allows user copy and zero copy

operations on the completed ublk request. It also triggers the

WARN_ON_ONCE(refcount_read(&io->ref)) warnings in ublk_queue_reinit()

and ublk_deinit_queue().

Commit c5c5eb24ed61 ("ublk: avoid ublk_io_release() called after ublk

char dev is closed") already fixed the issue for ublk devices using

UBLK_F_SUPPORT_ZERO_COPY or UBLK_F_AUTO

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References