CVE-2026-98478 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
scsi: ufs: core: Keep internal commands dispatchable during error handling
Commit 08b12cda6c44 ("scsi: ufs: core: Switch to scsi_get_internal_cmd()") switched UFS internal commands to allocate requests on hba->host->pseudo_sdev->request_queue, which shares the host tagset with regular LUNs.
During error recovery, ufshcd_err_handling_prepare() calls blk_mq_quiesce_tagset(&hba->host->tag_set), marking all queues in the tagset as quiesced, including pseudo_sdev->request_queue. When ufshcd_verify_dev_init() subsequently issues internal commands (e.g. NOP OUT UPIU) via blk_execute_rq(), blk_mq_run_hw_queue() skips running the quiesced queue, resulting in an unrecoverable circular wait deadlock.
Keep quiescing the tagset and unquiesce the pseudo SCSI device on top of that, so internal commands stay dispatchable while the logical units remain quiesced. Re-quiesce the pseudo device before unquiescing the tagset so that quiesce_depth stays balanced.
Clock scaling and ufshcd_pause_command_processing() are unaffected: they keep quiescing the whole tagset, internal commands included.
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Analysis
by VulDB Data Team • 10/19/2026
The vulnerability described involves a critical deadlock condition within the Universal Flash Storage (UFS) core subsystem of the Linux kernel, specifically affecting SCSI command handling during error recovery scenarios. The root cause stems from an architectural change introduced in commit 08b12cda6c44, which modified how UFS internal commands are allocated by directing them to a pseudo SCSI device request queue that shares its host tagset with regular Logical Unit Number (LUN) queues. This consolidation was intended to streamline resource management but inadvertently created a dependency conflict during system error handling procedures where the integrity of command dispatching is paramount for recovery operations.
During normal operation, this shared architecture functions adequately; however, it becomes problematic when the controller encounters an error requiring immediate intervention. The function ufshcd_err_handling_prepare initiates the error recovery process by calling blk_mq_quiesce_tagset on the host tag set. This action effectively pauses all queues associated with that tag set to prevent new commands from being dispatched while the system stabilizes. Because the pseudo SCSI device request queue shares this same tag set, it is also marked as quiesced along with the regular LUNs. Consequently, when subsequent recovery steps require the issuance of internal diagnostic or maintenance commands, such as NOP OUT UPIU packets via ufshcd_verify_dev_init(), these commands are submitted to a queue that has been explicitly halted from processing.
The operational impact is severe and manifests as an unrecoverable circular wait deadlock. When the kernel attempts to execute these necessary internal recovery commands using blk_execute_rq, the underlying hardware queue mechanism detects that the associated tag set is quiesced. As a result, blk_mq_run_hw_queue skips running the queue entirely rather than executing the pending requests. Since the error handling routine relies on the successful completion of these internal commands to verify device initialization and proceed with recovery, their indefinite suspension causes the entire error handling process to hang indefinitely. This leaves the storage subsystem in an unstable state where normal I/O operations are halted and automatic recovery mechanisms fail, potentially leading to system freezes or requiring a hard reset by the user.
To resolve this issue, the patch implements a targeted exception for internal commands during error handling phases. The solution involves keeping the main host tag set quiesced to maintain isolation of regular LUN traffic while explicitly unquiescing only the pseudo SCSI device queue associated with internal command dispatching. This ensures that critical recovery commands can proceed without interference from ongoing or pending user I/O operations. Furthermore, the fix includes logic to re-quiesce the pseudo device before fully unquiescing the main tag set at the end of the error handling process. This careful sequencing maintains balance in the quiesce depth counter, preventing reference count mismatches that could lead to other synchronization issues or resource leaks within the block layer subsystem.
From a vulnerability classification perspective, this defect aligns with CWE-835, which describes loops involving deadlock conditions where two or more processes are blocked forever waiting for each other. In terms of adversarial tactics and system behavior analysis, this scenario relates to ATT&CK technique T1496, Resource Hijacking, specifically in the context of Denial of Service through resource exhaustion or blocking. Although not exploitable by an external attacker for privilege escalation, it represents a significant reliability flaw that can be triggered by specific hardware error conditions, leading to service availability loss.
Mitigation strategies primarily involve applying the kernel patch that corrects the queue management logic during UFS error handling. For systems unable to immediately update their kernels, administrators should monitor storage subsystem logs for signs of I/O hangs or timeouts associated with UFS controllers and be prepared to perform manual resets if automatic recovery fails. Long-term resilience can be improved by ensuring robust hardware health monitoring so that underlying storage errors are detected early, allowing the system to handle them before they cascade into complex deadlock states within the driver layer. Regular kernel updates remain the most effective defense against such low-level synchronization flaws in critical infrastructure components.