High [CVE-2026-64034] Fix TOCTOU double-fetch of hwc_msg_id from DMA buffer

In the Linux kernel, the following vulnerability has been resolved: net: mana: Fix TOCTOU double-fetch of hwc_msg_id from DMA buffer In mana_hwc_rx_event_handler(), resp->response.hwc_msg_id is read from DMA-coherent memory and bounds-checked, then mana_hwc_handle_resp() re-reads the same field from the same DMA buffer for test_bit() and pointer arithmetic.

DMA-coherent memory is mapped uncacheable on x86 and is shared, unencrypted, in Confidential VMs (SEV-SNP/TDX), so each load goes directly to host-visible memory. A H/W can modify the value between the check and the use, bypassing the bounds validation.

Fix this by reading hwc_msg_id exactly once using READ_ONCE() into a stack-local variable in mana_hwc_rx_event_handler(), and passing the validated value as a parameter to mana_hwc_handle_resp(). A flaw was found in the Linux kernel's mana network driver.

This Time-of-Check to Time-of-Use (TOCTOU) vulnerability allows a hardware component to modify a message identifier (hwc_msg_id) in Direct Memory Access (DMA) memory after it has been validated but before it is used.

This manipulation bypasses critical bounds validation, potentially leading to unexpected system behavior or security bypasses, particularly in Confidential Virtual Machines (CVMs) where DMA memory is shared and unencrypted. Red Hat severity: Moderate — CVSS 7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H).