Vulnerability in Kernel: tty_buffer Softlockup Issue in flush_to_ldisc
Summary
UVI-2021-1002239: tty: tty_buffer: Fix the softlockup issue in flush_to_ldisc. Affects Kernel versions < 4c1623651a0936ee197859824cdae6ebbd04d3ed. No fix is published. How to fix ↓
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Background
The Kernel is a critical component of the Linux operating system that manages the system's resources and facilitates communication between hardware and software. It provides essential functionalities such as process management, memory management, and device drivers. The tty subsystem within the Kernel handles input and output operations for terminal devices. The tty_buffer module is responsible for buffering data before it is sent to the line discipline (ldisc). However, a vulnerability has been identified in the flush_to_ldisc function of the tty_buffer module, which can lead to a softlockup issue. This vulnerability can potentially be exploited by an attacker to cause a denial-of-service (DoS) condition or disrupt system operations.
Vulnerability Detail
The vulnerability arises from a flaw in the flush_to_ldisc function of the tty_buffer module. When flushing data to the line discipline, the function may enter an infinite loop, causing a softlockup. This can occur due to improper handling of certain conditions, leading to a situation where the function fails to exit the loop. An attacker with local access to the system could exploit this vulnerability by sending specially crafted input to a terminal device, triggering the softlockup and causing the system to become unresponsive. The impact of this vulnerability can range from a temporary system freeze to a complete system crash, depending on the severity of the softlockup.
How To Fix
No fixed version is published for this vulnerability.
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Workaround
As a temporary workaround, users can disable the affected functionality by unloading the tty_buffer module. This can be achieved by executing the following command as root:
rmmod tty_buffer
However, it is important to note that this workaround will disable the buffering functionality for terminal devices, which may impact the performance and reliability of input and output operations. Therefore, it is recommended to apply the official fix by updating the Kernel as soon as possible.
Conclusion
The vulnerability in the Kernel's tty_buffer module can result in a softlockup issue, potentially leading to a denial-of-service condition or system disruption. It is crucial to update the Linux Kernel to version v4.14.256 or later to mitigate this vulnerability. Users can obtain the updated Kernel from the official Linux Kernel repository. As a temporary workaround, the tty_buffer module can be unloaded, but this may impact the performance and reliability of terminal device operations. For further assistance and support in vulnerability remediation, please contact DevNack.com.
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FAQ
The Kernel is a critical component of the Linux operating system that manages system resources and facilitates communication between hardware and software. It provides essential functionalities such as process management, memory management, and device drivers.
The tty subsystem within the Kernel handles input and output operations for terminal devices. It provides the interface for interacting with terminals and serial ports.
The tty_buffer module is responsible for buffering data before it is sent to the line discipline (ldisc). It ensures efficient handling of input and output operations for terminal devices.
A softlockup refers to a situation where a system becomes unresponsive or experiences a significant delay due to a process or thread being stuck in an infinite loop or busy-waiting state.
This vulnerability can lead to a softlockup issue, causing the system to become unresponsive or crash. The severity of the impact depends on the severity of the softlockup and the criticality of the affected system.
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