CVE-2026-99183 in Linux
Summary
by MITRE • 10/28/2026
In the Linux kernel, the following vulnerability has been resolved:
accel/rocket: search every core slot when looking up a scheduler
sched_to_core() walks rdev->cores[] up to rdev->num_cores, and
rocket_remove() decrements num_cores for every core it removes. Unbind a core that is not the last one and the cores behind it fall outside the search, so sched_to_core() returns NULL for a core that is still bound and still running jobs. Neither caller checks the result:
rocket_job_run(): rocket_fence_create(core), core->dev rocket_job_timedout(): dev_err(core->dev, "NPU job timed out")
Unbinding the middle core of the three on an RK3588 while three clients are submitting to all of them faults twice, once from the surviving core's job queue and once from its reset work:
KASAN: null-ptr-deref in range [0x0000000000000220-0x0000000000000227]
Workqueue: fdad0000.npu drm_sched_run_job_work [gpu_sched]
pc : rocket_job_run+0x234/0x838 [rocket]
Call trace: rocket_job_run+0x234/0x838 [rocket]
drm_sched_run_job_work+0x2cc/0xad8 [gpu_sched]
process_one_work+0x640/0x14f0
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
Workqueue: rocket-reset-2 drm_sched_job_timedout [gpu_sched]
pc : rocket_job_timedout+0xf0/0x1e0 [rocket]
Call trace: rocket_job_timedout+0xf0/0x1e0 [rocket]
drm_sched_job_timedout+0x188/0x6a0 [gpu_sched]
Both are the third core: the workqueue names are its device and its core->index, and it was left at slot 2 while num_cores had dropped to 2.
Search all the slots that were allocated, the way find_core_for_dev() now does. A core that is still bound is then found, and the two callers get the pointer they already assume they have.
This does not make unbinding one core out of several safe. An open client keeps an entity pointing at the scheduler of the core that went away: drm_sched reports it as not ready for every job that lands on it, and the client waits in dma_fence_default_wait for a fence that will never signal. Stopping the NULL dereference is what belongs in a fix; the rest wants more thought.
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Analysis
by VulDB Data Team • 10/28/2026
The vulnerability identified within the Linux kernel's rocket accelerator driver represents a critical logic error in resource management during dynamic core unbinding operations, specifically affecting systems with multiple processing cores such as those based on the RK3588 SoC. The root cause lies in the implementation of the sched_to_core function, which is responsible for locating a specific scheduler instance associated with a hardware core. This function iterates through the rdev->cores array up to an upper bound defined by num_cores. However, when rocket_remove executes and unbinds a core that is not positioned at the end of this array, it decrements the num_cores counter immediately. Consequently, any cores located physically after the removed slot in memory but still logically active remain within bounds relative to their original indices yet fall outside the search range defined by the updated num_cores value. This creates a state where sched_to_core fails to locate valid scheduler structures for these remaining cores, returning NULL pointers instead of the expected object references.
The operational impact of this flaw is severe, manifesting as kernel panics due to null pointer dereferences in two distinct execution paths within the driver's job scheduling subsystem. The first crash occurs during normal operation when rocket_job_run attempts to create a fence for a core that was incorrectly deemed unavailable by sched_to_core. Because the function returned NULL instead of the valid core structure, subsequent access to core->dev results in an invalid memory read, triggering a KASAN null-ptr-deref fault within the drm_sched_run_job_work workqueue handler. The second crash arises from timeout handling mechanisms; when rocket_job_timedout is invoked for a job associated with one of these orphaned cores, it similarly attempts to access core->dev on a NULL pointer, causing another fatal exception in the rocket-reset-2 workqueue context. These crashes effectively deny service by crashing the kernel or forcing a system reboot whenever unbinding occurs mid-operation while active jobs are queued across multiple cores.
From a security and standards perspective, this vulnerability aligns with CWE-476, which describes NULL Pointer Dereference vulnerabilities resulting from improper error handling or state management logic. The flaw is not merely an input validation issue but rather a failure to maintain data structure integrity during dynamic configuration changes. In the context of the MITRE ATT&CK framework, this could be leveraged in scenarios involving Denial of Service against critical infrastructure components that rely on stable kernel subsystems for hardware acceleration tasks. While the immediate fix addresses the null pointer dereference by modifying sched_to_core to search all allocated slots rather than just those up to num_cores, it does not fully resolve the underlying architectural inconsistency regarding client entity references.
The provided patch ensures that sched_to_core correctly identifies active cores regardless of their position in the array relative to removed entries, thereby preventing the immediate crashes described above. However, as noted by the developers, this fix is partial because unbinding a core while clients are actively using it leaves open file descriptors and scheduler entities pointing toward non-existent or detached hardware resources. These dangling references cause client processes to hang indefinitely in dma_fence_default_wait, waiting for signal events that will never arrive from the removed core's scheduler. While stopping the kernel panic is essential for system stability, a complete resolution would require more comprehensive changes to handle resource cleanup and entity invalidation safely during hot-unplug scenarios, ensuring that no active context remains attached to decommissioned hardware resources.