CVE-2025-39816

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

io_uring/kbuf: always use READ_ONCE() to read ring provided buffer lengths

Since the buffers are mapped from userspace, it is prudent to use READ_ONCE() to read the value into a local variable, and use that for any other actions taken. Having a stable read of the buffer length avoids worrying about it changing after checking, or being read multiple times.

Similarly, the buffer may well change in between it being picked and being committed. Ensure the looping for incremental ring buffer commit stops if it hits a zero sized buffer, as no further progress can be made at that point.

This vulnerability is rated Moderate for Red Hat Enterprise Linux 10.x. The flaw exists in the io_uring/kbuf component of the kernel, where improper handling of ring provided buffer lengths from userspace could lead to an issue. Red Hat Enterprise Linux 6, 7, 8, and 9 are not affected as the vulnerable code is not present in these versions. If triggered, this vulnerability affects integrity and availability, as the bug can cause inconsistent internal states and lead to stalls or system instability in the io_uring subsystem.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.