CVE-2026-90144 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
dpll: fix NULL deref in dpll_device_ops() during teardown race
When the last owner of a dpll device unregisters while a foreign driver still holds a pin on it via dpll_pin_on_pin_register(), the dpll object stays alive with an empty registration list. A pin notification queued before the unregister (e.g. ice reacting to zl3073x_i2c removal) then walks pin->dpll_refs into dpll_device_ops(), which trips the WARN_ON and dereferences the missing registration. dpll_lock cannot help because the notification work was queued before the unregistering driver took the lock.
Treat the empty registration list as a legitimate transient state. Make dpll_priv() and dpll_device_ops() return NULL in that case and make every pin netlink path that resolves a device from a pin skip such dplls. dpll_cmd_pin_get_one() picks a ref with a live registration and returns -ENODEV when there is none, the pin dumpit skips such a pin instead of aborting the dump, dpll_msg_add_pin_dplls() and the frequency, esync, reference sync and phase adjust set paths skip dead refs, and dpll_pin_parent_device_set() validates the parent with dpll_device_get_by_id(). dpll_pin_register() is the last caller that dereferenced the device ops without a check, so move its frequency monitor validation under dpll_lock and tolerate a missing registration there as well.
The empty registration list is equivalent to a cleared DPLL_REGISTERED mark, both transitions happen under dpll_lock in dpll_device_register() and dpll_device_unregister(). A pin notification for a pin whose dplls are all gone is now dropped with -ENODEV instead of crashing, all callers in the core ignore that return value.
WARNING: drivers/dpll/dpll_core.c:1092 at dpll_device_ops+0x24/0x40, CPU#83: kworker/u576:3/23471 Modules linked in: ... ice ... zl3073x_i2c(-) ... zl3073x ... Workqueue: ice_dpll_wq ice_dpll_pin_notify_work [ice]
RIP: 0010:dpll_device_ops+0x24/0x40 Call Trace: <TASK> dpll_cmd_pin_get_one+0x336/0x520 dpll_pin_event_send+0x82/0x140 dpll_pin_on_pin_unregister+0xbb/0x160 ice_dpll_pin_notify_work+0x1bc/0x1f0 [ice]
process_one_work+0x19e/0x370 worker_thread+0x1a6/0x310 kthread+0xe4/0x120 ret_from_fork+0x1a1/0x270 ret_from_fork_asm+0x1a/0x30 </TASK> ---[ end trace 0000000000000000 ]---
BUG: kernel NULL pointer dereference, address: 0000000000000010 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel's Dynamic Phase-Locked Loop subsystem contains a race condition vulnerability that results in a NULL pointer dereference during device teardown operations. This flaw occurs when the last owner of a DPLL device unregisters while a foreign driver still holds an active pin reference via dpll_pin_on_pin_register(). In this specific scenario, the DPLL object remains alive but its internal registration list becomes empty because it has been logically removed from the system's active registry. However, pending notifications that were queued prior to the unregister operation continue to execute asynchronously. When such a notification triggers work in an external driver like ice reacting to hardware removal events such as zl3073x_i2c unbinding, the code attempts to traverse pin->dpll_refs and invoke dpll_device_ops(). Because the registration list is empty, this traversal leads directly to a NULL pointer dereference. The standard locking mechanism provided by dpll_lock fails to prevent this issue because the notification work was queued before the unregistering driver acquired the lock, creating a window where state changes are not synchronized with pending asynchronous tasks.
This vulnerability represents a classic use-after-free or null-dereference scenario arising from improper handling of transient states in concurrent environments. From a classification perspective, it aligns with CWE-476 NULL Pointer Dereference and reflects weaknesses associated with race conditions such as those described under CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization. The operational impact is severe, leading to kernel panics or system crashes that disrupt availability for critical infrastructure components relying on precise clock synchronization. The trace logs indicate the crash occurs in supervisor mode during a read access attempt at address zero, confirming the dereference of an invalid pointer within the core DPLL management logic. Such instability can cause significant downtime in data centers and telecommunications equipment where phase-locked loops are essential for maintaining signal integrity across network interfaces.
The resolution involves treating the empty registration list as a legitimate transient state rather than an error condition that should trigger immediate failure or crash. The fix modifies dpll_priv() and dpll_device_ops() to return NULL when no active registrations exist, effectively neutralizing the dereference risk. Furthermore, every pin netlink path that resolves a device from a pin is updated to skip DPLLs lacking live registrations. Specific functions such as dpll_cmd_pin_get_one now select references with valid registrations and return -ENODEV if none are found. The pin dumpit functionality skips pins associated with dead DPLLs instead of aborting the entire dump operation, ensuring system stability during diagnostic queries. Additionally, message handling paths for frequency control, external synchronization, reference sync, and phase adjustment set operations now explicitly skip references to inactive devices.
To ensure comprehensive protection against this race condition, dpll_pin_parent_device_set() was updated to validate parent existence using dpll_device_get_by_id(), preventing access to unregistered parents. Crucially, the final caller that previously dereferenced device ops without adequate checks is addressed by moving its frequency monitor validation under the scope of dpll_lock. This adjustment ensures that even if a registration disappears during execution, the operation tolerates the missing state gracefully rather than crashing. The empty registration list is now treated as equivalent to a cleared DPLL_REGISTERED mark, with both transitions occurring safely under lock protection in register and unregister functions. Consequently, pin notifications for pins whose associated DPLLs have all been removed are dropped with an -ENODEV error code instead of causing a kernel panic. All callers within the core subsystem ignore this return value appropriately, ensuring robust handling of edge cases during device lifecycle management. This fix significantly enhances the resilience of the Linux kernel against timing-dependent vulnerabilities in hardware abstraction layers used for high-precision clocking systems.