CVE-2026-74754 in Linux
Summary
by MITRE • 08/26/2026
In the Linux kernel, the following vulnerability has been resolved:
scsi: core: pair EH runtime PM get and put
shost->eh_noresume is currently consulted twice in one error handling iteration: once before scsi_autopm_get_host() and once again before scsi_autopm_put_host().
That is racy when a PM-triggered error path flips shost->eh_noresume while the SCSI EH thread is still running.
The problem flow looks like this: PM path ufshcd_set_dev_pwr_mode() shost->eh_noresume = 1 ufshcd_execute_start_stop <-- trigger EH ... shost->eh_noresume = 0
EH path scsi_error_handler() if (!shost->eh_noresume) scsi_autopm_get_host() <-- skipped ... if (!shost->eh_noresume) scsi_autopm_put_host() <-- executed later
In that case one EH iteration can skip autoresume on entry and still drop a runtime PM reference on exit. That leaves an unmatched runtime PM put and can trigger a runtime PM usage count underflow.
Fix this by making eh_noresume a regular bool so it can be accessed with READ_ONCE() and WRITE_ONCE(). Snapshot it once per EH iteration and use that snapshot for both runtime PM get and put decisions.
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Analysis
by VulDB Data Team • 08/26/2026
The Linux kernel SCSI subsystem contains a race condition within the error handling mechanism related to power management reference counting, specifically involving the interaction between the host adapter's no-resume flag and automatic power management functions. The vulnerability stems from an inconsistent check of the shost->eh_noresume variable during a single iteration of the SCSI error handler. In the original implementation, this boolean flag is consulted twice: once before invoking scsi_autopm_get_host to acquire a runtime power management reference, and again before calling scsi_autopm_put_host to release that reference. This dual-check approach creates a window for race conditions where concurrent operations can alter the state of shost->eh_noresume between these two calls, leading to an imbalance in the device's runtime PM usage count.
The operational impact arises when a power management triggered error path modifies the eh_nosuspend flag while the SCSI error handler thread is actively executing. For instance, during a UFS host controller operation such as setting device power mode or starting stop operations, the system may set shost->eh_noresume to one and subsequently reset it to zero within a short timeframe. If this transition occurs between the initial check for acquiring the PM reference and the subsequent check for releasing it, the error handler may skip the acquisition of the runtime PM get due to the flag being true at that moment, but still proceed to execute the put operation because the flag has since reverted to false. This results in an unmatched runtime PM put call, which decrements the usage count below zero, causing a runtime PM underflow condition. Such underflows can lead to system instability, unexpected device suspensions, or kernel panics due to corrupted power management state tracking.
This vulnerability is classified as CWE-362, Concurrent Execution using Shared Resource with Improper Synchronization, commonly known as a race condition. The specific failure mode involves improper synchronization of shared data structures across different execution contexts, namely the power management path and the SCSI error handling thread. From an ATT&CK perspective, this aligns with techniques involving resource manipulation that could lead to denial of service or system instability if exploited in conjunction with other vulnerabilities, although primarily it represents a stability issue rather than a direct security exploit vector for privilege escalation. The root cause is identified as CWE-367, Time-of-check Time-of-use (TOCTOU) race condition, where the state checked at one point in time differs from the state used later in the same logical operation.
The resolution involves refactoring the handling of the eh_noresume flag to ensure atomicity and consistency within a single error handler iteration. The fix changes eh_noresume to be accessed using READ_ONCE() and WRITE_ONCE macros, which prevent compiler optimizations that might reorder or cache memory accesses in ways that exacerbate race conditions. More importantly, the logic is modified to snapshot the value of shost->eh_noresume once at the beginning of each error handling iteration. This single snapshot is then used for both decisions regarding whether to acquire and release runtime power management references. By ensuring that both get and put operations rely on the same consistent state observed at a specific point in time, the race window is eliminated, preventing scenarios where one operation is skipped while the other proceeds, thereby maintaining correct reference counting balance.
To mitigate this issue, systems running affected versions of the Linux kernel should be updated to include the patch that implements these synchronization improvements. Administrators and developers monitoring system logs for power management errors or unexpected device suspensions should verify that their kernels incorporate fixes related to SCSI core error handling race conditions. While this vulnerability primarily affects system stability rather than providing a direct avenue for unauthorized access, maintaining correct kernel state is critical for overall security posture as instability can lead to exploitable states in other subsystems. Regular updates and adherence to vendor-recommended patching schedules are essential to address such low-level concurrency bugs that compromise the integrity of core operating system functions.