CVE-2024-46735 in Linux
Summary
by MITRE • 09/18/2024
In the Linux kernel, the following vulnerability has been resolved:
ublk_drv: fix NULL pointer dereference in ublk_ctrl_start_recovery()
When two UBLK_CMD_START_USER_RECOVERY commands are submitted, the first one sets 'ubq->ubq_daemon' to NULL, and the second one triggers WARN in ublk_queue_reinit() and subsequently a NULL pointer dereference issue.
Fix it by adding the check in ublk_ctrl_start_recovery() and return immediately in case of zero 'ub->nr_queues_ready'.
BUG: kernel NULL pointer dereference, address: 0000000000000028 RIP: 0010:ublk_ctrl_start_recovery.constprop.0+0x82/0x180 Call Trace: ? __die+0x20/0x70 ? page_fault_oops+0x75/0x170 ? exc_page_fault+0x64/0x140 ? asm_exc_page_fault+0x22/0x30 ? ublk_ctrl_start_recovery.constprop.0+0x82/0x180 ublk_ctrl_uring_cmd+0x4f7/0x6c0 ? pick_next_task_idle+0x26/0x40 io_uring_cmd+0x9a/0x1b0 io_issue_sqe+0x193/0x3f0 io_wq_submit_work+0x9b/0x390 io_worker_handle_work+0x165/0x360 io_wq_worker+0xcb/0x2f0 ? finish_task_switch.isra.0+0x203/0x290 ? finish_task_switch.isra.0+0x203/0x290 ? __pfx_io_wq_worker+0x10/0x10 ret_from_fork+0x2d/0x50 ? __pfx_io_wq_worker+0x10/0x10 ret_from_fork_asm+0x1a/0x30
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Analysis
by VulDB Data Team • 04/05/2026
The vulnerability identified as CVE-2024-46735 resides within the Linux kernel's ublk driver, specifically affecting the ublk_ctrl_start_recovery() function. This issue manifests as a NULL pointer dereference that occurs when two UBLK_CMD_START_USER_RECOVERY commands are submitted in sequence. The first command properly initializes the ubq_daemon field to NULL, while the second command triggers a warning in the ublk_queue_reinit() function, ultimately leading to a critical NULL pointer dereference condition. The root cause stems from insufficient validation within the recovery control mechanism, where the driver fails to properly handle the case when the queue recovery process is already in progress or has been completed. This vulnerability represents a classic race condition scenario where concurrent operations on shared kernel data structures result in undefined behavior and potential system instability.
The technical flaw exists in the ublk driver's control command processing logic where the ublk_ctrl_start_recovery() function does not adequately validate the state of the underlying queue structure before proceeding with recovery operations. When the second recovery command is processed, the function attempts to dereference a NULL pointer that was set by the first command, creating a kernel oops condition that can lead to system crashes or potential privilege escalation. The kernel's memory management system detects this invalid memory access at address 0x0000000000000028, which corresponds to a critical data structure field within the ublk queue management system. The call trace demonstrates the execution path leading to the fault, showing how the io_uring subsystem processes the recovery command through multiple kernel layers before the NULL pointer dereference occurs, indicating a deep integration of the vulnerability within the kernel's asynchronous I/O handling framework.
The operational impact of this vulnerability extends beyond simple system crashes, as it can potentially be exploited to cause denial of service conditions or, in more sophisticated attack scenarios, could provide a foothold for privilege escalation within the kernel space. The vulnerability affects systems utilizing the ublk (user block) driver functionality, which is commonly used for implementing user-space block devices and storage backends. The NULL pointer dereference creates a kernel oops condition that typically results in immediate system termination through a kernel panic, making this particularly dangerous in production environments where system reliability is critical. From a cybersecurity perspective, this vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and could potentially map to ATT&CK technique T1068 under "Exploitation for Privilege Escalation" if exploited in a manner that allows privilege elevation. The vulnerability's exploitation requires local access to submit the malicious commands, but the impact can be severe enough to warrant immediate attention.
The fix implemented addresses the vulnerability by introducing a validation check within the ublk_ctrl_start_recovery() function to verify the state of ub->nr_queues_ready before proceeding with recovery operations. This simple yet critical change ensures that the function returns immediately when the queue readiness count is zero, preventing the subsequent NULL pointer dereference. The patch demonstrates a defensive programming approach that prevents the driver from operating on already-processed or invalid queue states. Organizations should prioritize applying this kernel update as it resolves a critical stability issue that could be exploited to cause system-wide outages. The mitigation strategy should include monitoring for any unusual system behavior or kernel oops messages that might indicate exploitation attempts, while also ensuring that all systems running kernel versions containing this vulnerability are updated to the patched version. The fix maintains backward compatibility while strengthening the driver's resilience against concurrent command processing scenarios, aligning with industry best practices for kernel security hardening and robust error handling in device drivers.