CVE-2024-40967 in Linux
Summary
by MITRE • 07/12/2024
In the Linux kernel, the following vulnerability has been resolved:
serial: imx: Introduce timeout when waiting on transmitter empty
By waiting at most 1 second for USR2_TXDC to be set, we avoid a potential deadlock.
In case of the timeout, there is not much we can do, so we simply ignore the transmitter state and optimistically try to continue.
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Analysis
by VulDB Data Team • 09/30/2024
The vulnerability identified as CVE-2024-40967 resides within the Linux kernel's serial communication subsystem, specifically affecting the imx serial driver implementation. This flaw manifests as a potential deadlock condition that can occur during transmitter state management, particularly when the system waits indefinitely for a specific hardware register flag to be set. The imx serial driver is commonly used in embedded systems and automotive applications where reliable serial communication is critical for system operation. The vulnerability impacts systems that utilize i.MX series processors from NXP, which are widely deployed in industrial control systems, automotive electronics, and embedded devices where serial port communication is essential for data transfer and device control.
The technical root cause of this vulnerability stems from the driver's implementation of transmitter state waiting mechanisms without proper timeout handling. When the system attempts to send data through the serial port, it waits for the USR2_TXDC flag to be set, indicating that the transmitter is empty and ready for new data. However, the absence of a timeout mechanism means that if this flag fails to set properly due to hardware issues, driver bugs, or unexpected system conditions, the kernel thread can block indefinitely. This represents a classic deadlock scenario where the system becomes unresponsive while waiting for a condition that may never occur, potentially leading to complete system hangs or unresponsiveness in embedded environments where serial communication is critical for system functionality.
The operational impact of this vulnerability extends beyond simple system hangs to potentially compromise the reliability and availability of embedded systems that depend on serial communication for critical operations. In automotive applications, this could result in communication failures between control units, potentially affecting vehicle safety systems or diagnostic capabilities. Industrial control systems may experience complete communication breakdowns, leading to production halts or process failures. The timeout mechanism introduced in the fix addresses this by limiting wait time to one second, which aligns with industry best practices for preventing indefinite blocking operations. When the timeout occurs, the driver employs an optimistic approach by continuing operation rather than failing completely, though this may lead to data transmission errors that require application-level handling.
The fix for CVE-2024-40967 demonstrates proper adherence to security engineering principles by implementing defensive programming techniques that prevent resource exhaustion and system unresponsiveness. This approach aligns with CWE-362, which addresses race conditions and concurrency issues that can lead to system instability, and follows ATT&CK framework concept T1499.004 related to resource exhaustion attacks. The solution prevents potential denial of service conditions that could be exploited by malicious actors to cause system unresponsiveness, while maintaining system operability through the optimistic continuation approach. This represents a balanced security measure that prioritizes system availability over absolute data integrity in edge cases, which is appropriate for embedded systems where complete system failure is more detrimental than occasional transmission errors. The implementation follows established kernel development practices for handling hardware communication timeouts and demonstrates the importance of proper timeout handling in kernel-level device drivers to prevent system-level stability issues.