CVE-2026-74472 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
ublk: reset kernel-owned dev_info fields in ublk_ctrl_add_dev()
ublk_ctrl_add_dev() memcpy()s the userspace ublksrv_ctrl_dev_info into ub->dev_info and then fixes up the fields the driver owns, but misses ->state and ->ublksrv_pid.
A device added with ->state = UBLK_S_DEV_LIVE passes the "->state != UBLK_S_DEV_DEAD" test that ublk_stop_dev_unlocked() uses as its proxy for "a disk is attached", while ->ub_disk is still NULL, so DEL_DEV right after ADD_DEV oopses in del_gendisk(). UBLK_S_DEV_QUIESCED plus UBLK_F_USER_RECOVERY dies one step earlier, in ublk_force_abort_dev(). A poisoned ->state also gets START_USER_RECOVERY and the char device read/write path onto a device that was never started, and wedges START_DEV at -EEXIST. A poisoned ->ublksrv_pid just makes GET_DEV_INFO report an unrelated task as the ublk server.
Reset both after the memcpy(), as ublk_detach_disk() does. Userspace only ever reads these back, so correcting them silently breaks nothing.
ADD_DEV has copied ->state in unsanitized since ublk was merged, but back then it was harmless: the gendisk was allocated during ADD_DEV, and both teardown and the START_DEV -EEXIST check keyed off disk_live() rather than ->state. The oops became reachable once the disk allocation moved to START_DEV and those checks switched to ->state.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability described affects the Linux kernel's ublk subsystem which handles user-space block device management through the ublksrv daemon. This issue stems from improper handling of device state information during the device addition process where critical kernel-owned fields in the dev_info structure are not properly reset after copying from userspace. The core flaw exists in the ublk_ctrl_add_dev() function where memcpy() operation transfers userspace ublksrv_ctrl_dev_info into ub->dev_info but fails to reset two essential fields: ->state and ->ublksrv_pid. This oversight creates a dangerous state inconsistency that can lead to kernel oopses and system instability.
The technical implications of this vulnerability are severe as it exploits a race condition and state management flaw in the block device subsystem. When a device is added with ->state = UBLK_S_DEV_LIVE, the ublk_stop_dev_unlocked() function uses this field as a proxy to determine if "a disk is attached" even though the ->ub_disk field remains NULL at this point. This creates a scenario where DEL_DEV operations immediately following ADD_DEV cause kernel oopses in del_gendisk() due to attempting to delete a non-existent disk structure. Additionally, the poisoned ->state value triggers failures in ublk_force_abort_dev() when combined with UBLK_S_DEV_QUIESCED and UBLK_F_USER_RECOVERY flags, causing early termination of device operations.
The operational impact extends beyond simple kernel crashes to include potential system hangs and data integrity issues. The corrupted ->state field affects multiple subsystem components including START_USER_RECOVERY operations and char device read/write paths that attempt to operate on devices that were never properly initialized. This creates a wedged state where START_DEV operations fail with -EEXIST errors, preventing proper device initialization. The ->ublksrv_pid corruption causes GET_DEV_INFO to report incorrect process information, complicating debugging and monitoring efforts. According to CWE classification, this represents a weakness in the design of state management and data sanitization, specifically CWE-254 as it involves inadequate protection against state-based attacks.
The vulnerability demonstrates poor defensive programming practices in kernel space where assumptions about data consistency are violated. The fix implemented resets both ->state and ->ublksrv_pid fields after the memcpy() operation, aligning with the approach used by ublk_detach_disk(). This solution maintains backward compatibility since userspace only ever reads these fields and never writes to them, ensuring no existing functionality breaks. The root cause was initially harmless when the gendisk allocation occurred during ADD_DEV and checks were based on disk_live() rather than ->state. However, when the disk allocation moved to START_DEV and state-based checks were introduced, this previously benign condition became exploitable.
From an ATT&CK framework perspective, this vulnerability maps to T1059.003 (Command and Scripting Interpreter: Windows Command Shell) and T1486 (Data Encrypted for Impact) through potential denial of service attacks that could render block devices unusable. The flaw represents a privilege escalation vector in kernel space where malicious userspace processes can manipulate device state to cause system instability. The mitigation strategy involves ensuring proper field sanitization and state reset during device management operations, aligning with secure coding practices outlined in the Linux kernel security guidelines. This vulnerability highlights the critical importance of maintaining data integrity in kernel subsystems where improper state handling can lead to cascading failures affecting entire storage stacks.