CVE-2024-35968 in Linux
Summary
by MITRE • 05/20/2024
In the Linux kernel, the following vulnerability has been resolved:
pds_core: Fix pdsc_check_pci_health function to use work thread
When the driver notices fw_status == 0xff it tries to perform a PCI reset on itself via pci_reset_function() in the context of the driver's health thread. However, pdsc_reset_prepare calls pdsc_stop_health_thread(), which attempts to stop/flush the health thread. This results in a deadlock because the stop/flush will never complete since the driver called pci_reset_function() from the health thread context. Fix by changing the pdsc_check_pci_health_function() to queue a newly introduced pdsc_pci_reset_thread() on the pdsc's work queue.
Unloading the driver in the fw_down/dead state uncovered another issue, which can be seen in the following trace:
WARNING: CPU: 51 PID: 6914 at kernel/workqueue.c:1450 __queue_work+0x358/0x440 [...]
RIP: 0010:__queue_work+0x358/0x440 [...]
Call Trace: ? __warn+0x85/0x140 ? __queue_work+0x358/0x440 ? report_bug+0xfc/0x1e0 ? handle_bug+0x3f/0x70 ? exc_invalid_op+0x17/0x70 ? asm_exc_invalid_op+0x1a/0x20 ? __queue_work+0x358/0x440 queue_work_on+0x28/0x30 pdsc_devcmd_locked+0x96/0xe0 [pds_core]
pdsc_devcmd_reset+0x71/0xb0 [pds_core]
pdsc_teardown+0x51/0xe0 [pds_core]
pdsc_remove+0x106/0x200 [pds_core]
pci_device_remove+0x37/0xc0 device_release_driver_internal+0xae/0x140 driver_detach+0x48/0x90 bus_remove_driver+0x6d/0xf0 pci_unregister_driver+0x2e/0xa0 pdsc_cleanup_module+0x10/0x780 [pds_core]
__x64_sys_delete_module+0x142/0x2b0 ? syscall_trace_enter.isra.18+0x126/0x1a0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc RIP: 0033:0x7fbd9d03a14b [...]
Fix this by preventing the devcmd reset if the FW is not running.
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Analysis
by VulDB Data Team • 05/20/2024
The vulnerability described in CVE-2024-35968 affects the Linux kernel's pds_core driver component, specifically within the pds_core module responsible for managing PCI device health monitoring. This issue manifests as a deadlock condition that occurs during driver operation when firmware status indicates a critical failure state. The root cause lies in the improper handling of PCI reset operations within the driver's health monitoring thread context, creating a circular dependency that prevents normal system operation and potentially leads to system hangs.
The technical flaw stems from a design conflict in the driver's health monitoring mechanism where the pdsc_check_pci_health function attempts to execute pci_reset_function() directly from within the health thread context. When firmware status equals 0xff, indicating a critical failure, the driver triggers a PCI reset operation but simultaneously calls pdsc_stop_health_thread() to halt the health monitoring thread. This creates an irreconcilable deadlock scenario because the thread stopping mechanism cannot complete while the PCI reset operation is actively running within the same thread context. This specific type of deadlock falls under CWE-362, which describes concurrent execution issues where a thread cannot be properly terminated due to its own execution context.
The operational impact of this vulnerability extends beyond simple system hangs to potentially compromise system stability and availability. During normal operation, the driver's health monitoring thread becomes unresponsive when encountering firmware failures, preventing proper error recovery and system maintenance. The vulnerability becomes particularly dangerous during driver unloading operations when the system attempts to clean up resources while the firmware is in a dead state. The kernel warning trace reveals that the system attempts to queue work items during driver removal but fails due to the driver's inability to properly handle the reset operation when firmware is not in a running state, leading to potential system crashes or unrecoverable states.
The mitigation strategy implemented in the fix involves restructuring the driver's reset mechanism by introducing a dedicated pdsc_pci_reset_thread() function that operates on the driver's work queue rather than within the health thread context. This change eliminates the circular dependency by decoupling the PCI reset operation from the health monitoring thread, allowing proper thread management and resource cleanup. The fix also addresses the secondary issue discovered during driver unloading by preventing devcmd reset operations when firmware is not running, thereby avoiding the problematic queue_work_on call that was causing the kernel warning. This solution aligns with ATT&CK technique T1489 which involves system shutdown or reboot attacks, as it prevents the system from entering an unrecoverable state due to improper resource management and thread handling during driver cleanup operations. The implementation follows proper kernel development practices by ensuring that device reset operations occur in appropriate contexts and that thread lifecycle management maintains system stability during both normal operation and error recovery scenarios.