CVE-2026-98286: Linux kernel · drop_monitor: use timer_shutdown_sync() to prevent timer rearming during teardown

In the Linux kernel, the following vulnerability has been resolved: drop_monitor: use timer_shutdown_sync() to prevent timer rearming during teardown In drop_monitor teardown paths (net_dm_trace_off_set(), net_dm_hw_monitor_stop(), and error unwind paths in net_dm_trace_on_set() and net_dm_hw_monitor_start()), per-CPU timers are stopped using timer_delete_sync() followed by cancel_work_sync(). However, there is a circular dependency between send_timer and dm_alert_work: 1) sched_send_work() (timer callback) schedules dm_alert_work. 2) send_dm_alert() / net_dm_hw_summary_work() calls reset_per_cpu_data() or net_dm_hw_reset_per_cpu_data(). 3) If memory allocation fails under memory pressure in the reset function, it re-arms the timer via mod_timer(&data->send_timer, ...). If dm_alert_work is running concurrently while timer_delete_sync() executes on another CPU, an allocation failure in the worker will re-arm the timer after timer_delete_sync() has already returned. Once cancel_work_sync() completes and module_put() is called, the timer remains active in the timer wheel. If the module is then unloaded, the timer will fire and execute sched_send_work() in freed memory, triggering a kernel panic / use-after-free. Switch from timer_delete_sync() to timer_shutdown_sync(). This guarantees that any in-flight timer handler has finished and prevents subsequent re-arming attempts from running workers from succeeding. When monitoring is restarted later, timer_setup() is invoked, which cleanly re-initializes the timer.

• ubuntu.com/security/CVE-2026-98286 (opens in a new tab)
• cve.org/CVERecord?id=CVE-2026-98286 (opens in a new tab)
• git.kernel.org/linus/c391a40f71886b28c082b47270f0e856fa3e1150 (opens in a new tab)
• git.kernel.org/stable/c/9616b0c67fbd8cc0b49de7b26cdf2ab33747c80e (opens in a new tab)
• git.kernel.org/stable/c/bda4d9525fb91a2388ee09669421b8d505290864 (opens in a new tab)
• git.kernel.org/stable/c/c391a40f71886b28c082b47270f0e856fa3e1150 (opens in a new tab)

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