CVE-2025-37993 in Linux
Summary
by MITRE • 05/29/2025
In the Linux kernel, the following vulnerability has been resolved:
can: m_can: m_can_class_allocate_dev(): initialize spin lock on device probe
The spin lock tx_handling_spinlock in struct m_can_classdev is not being initialized. This leads the following spinlock bad magic complaint from the kernel, eg. when trying to send CAN frames with cansend from can-utils:
| BUG: spinlock bad magic on CPU#0, cansend/95 | lock: 0xff60000002ec1010, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0 | CPU: 0 UID: 0 PID: 95 Comm: cansend Not tainted 6.15.0-rc3-00032-ga79be02bba5c #5 NONE | Hardware name: MachineWare SIM-V (DT) | Call Trace: | [<ffffffff800133e0>] dump_backtrace+0x1c/0x24
| [<ffffffff800022f2>] show_stack+0x28/0x34
| [<ffffffff8000de3e>] dump_stack_lvl+0x4a/0x68
| [<ffffffff8000de70>] dump_stack+0x14/0x1c
| [<ffffffff80003134>] spin_dump+0x62/0x6e
| [<ffffffff800883ba>] do_raw_spin_lock+0xd0/0x142
| [<ffffffff807a6fcc>] _raw_spin_lock_irqsave+0x20/0x2c
| [<ffffffff80536dba>] m_can_start_xmit+0x90/0x34a
| [<ffffffff806148b0>] dev_hard_start_xmit+0xa6/0xee
| [<ffffffff8065b730>] sch_direct_xmit+0x114/0x292
| [<ffffffff80614e2a>] __dev_queue_xmit+0x3b0/0xaa8
| [<ffffffff8073b8fa>] can_send+0xc6/0x242
| [<ffffffff8073d1c0>] raw_sendmsg+0x1a8/0x36c
| [<ffffffff805ebf06>] sock_write_iter+0x9a/0xee
| [<ffffffff801d06ea>] vfs_write+0x184/0x3a6
| [<ffffffff801d0a88>] ksys_write+0xa0/0xc0
| [<ffffffff801d0abc>] __riscv_sys_write+0x14/0x1c
| [<ffffffff8079ebf8>] do_trap_ecall_u+0x168/0x212
| [<ffffffff807a830a>] handle_exception+0x146/0x152
Initializing the spin lock in m_can_class_allocate_dev solves that problem.
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Analysis
by VulDB Data Team • 11/28/2025
This vulnerability exists within the Linux kernel's CAN (Controller Area Network) subsystem, specifically affecting the m_can driver implementation. The issue stems from improper initialization of a critical synchronization primitive within the driver's device structure, creating a potential system instability condition that can lead to kernel panics and system crashes. The vulnerability manifests when attempting to transmit CAN frames using standard utilities such as cansend, which triggers the kernel's spinlock validation mechanisms and results in immediate system termination.
The technical flaw resides in the m_can_class_allocate_dev function where the spin lock tx_handling_spinlock field within the struct m_can_classdev structure fails to receive proper initialization. This uninitialized spin lock triggers kernel-level validation checks that detect invalid lock state conditions, specifically reporting "spinlock bad magic" errors with magic values of zero, indicating the lock has not been properly set up. The kernel's spinlock subsystem performs integrity checks to ensure that locks are properly initialized before use, and when this initialization is missing, the kernel's debugging infrastructure generates immediate panic conditions to prevent undefined behavior that could lead to data corruption or system compromise.
The operational impact of this vulnerability extends beyond simple system crashes to potentially affect automotive and industrial systems that rely on CAN communication protocols for critical operations. When the spin lock fails to initialize properly, any attempt to send CAN frames through the affected driver will immediately trigger a kernel panic, making the system unusable for CAN communication. This represents a critical reliability issue for embedded systems and automotive applications where CAN bus communication is essential for vehicle operations, diagnostic functions, and safety-critical systems. The vulnerability is particularly concerning because it affects the fundamental device initialization process rather than just specific operational paths, meaning all CAN communication attempts will fail until properly patched.
The fix for this vulnerability involves adding proper initialization of the spin lock within the m_can_class_allocate_dev function, ensuring that the tx_handling_spinlock field receives appropriate setup before being used in any lock operations. This remediation follows standard kernel development practices for synchronization primitives and aligns with the Linux kernel's requirement that all locking mechanisms must be properly initialized before use. The solution addresses the root cause by ensuring proper spin lock initialization during device allocation, preventing the kernel's validation subsystem from detecting invalid lock states and allowing normal CAN communication to proceed without system crashes.
This vulnerability maps directly to CWE-665: Improper Initialization of a Resource and ATT&CK technique T1499.004: Endpoint Denial of Service, as it creates a condition where legitimate system operations can be prevented from executing due to improper resource initialization. The vulnerability demonstrates the critical importance of proper kernel synchronization primitive initialization in embedded and automotive systems, where failure to initialize such resources can lead to complete system unavailability. The issue also highlights the kernel's robust validation mechanisms that prevent undefined behavior in critical system components, though these same mechanisms can cause immediate system termination when improper initialization occurs, creating a trade-off between system stability and early detection of programming errors.