CVE-2021-47153 in Linux
Summary
by MITRE • 03/25/2024
In the Linux kernel, the following vulnerability has been resolved:
i2c: i801: Don't generate an interrupt on bus reset
Now that the i2c-i801 driver supports interrupts, setting the KILL bit in a attempt to recover from a timed out transaction triggers an interrupt. Unfortunately, the interrupt handler (i801_isr) is not prepared for this situation and will try to process the interrupt as if it was signaling the end of a successful transaction. In the case of a block transaction, this can result in an out-of-range memory access.
This condition was reproduced several times by syzbot: https://syzkaller.appspot.com/bug?extid=ed71512d469895b5b34e https://syzkaller.appspot.com/bug?extid=8c8dedc0ba9e03f6c79e https://syzkaller.appspot.com/bug?extid=c8ff0b6d6c73d81b610e https://syzkaller.appspot.com/bug?extid=33f6c360821c399d69eb https://syzkaller.appspot.com/bug?extid=be15dc0b1933f04b043a https://syzkaller.appspot.com/bug?extid=b4d3fd1dfd53e90afd79
So disable interrupts while trying to reset the bus. Interrupts will be enabled again for the following transaction.
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Analysis
by VulDB Data Team • 09/16/2025
The vulnerability described in CVE-2021-47153 affects the Linux kernel's i2c-i801 driver implementation, specifically addressing a critical race condition and improper interrupt handling during bus reset operations. This flaw exists within the Intel 801 I2C controller driver which manages communication between the system and various hardware devices through the I2C protocol. The issue manifests when the driver attempts to recover from a timed-out transaction by setting the KILL bit to reset the bus, a common recovery mechanism in I2C communication systems. The vulnerability stems from the driver's failure to properly account for interrupt generation during the bus reset process, creating a scenario where interrupt handling occurs in an unexpected context.
The technical flaw occurs when the i801_isr interrupt handler receives an interrupt signal during a bus reset operation that was initiated by setting the KILL bit. This interrupt is not properly filtered or handled by the interrupt service routine, which assumes all interrupts indicate successful transaction completion. As a result, when processing block transactions, the interrupt handler attempts to access memory locations beyond the allocated buffer boundaries, leading to potential memory corruption and system instability. This type of out-of-bounds memory access represents a classic buffer overflow vulnerability that can be exploited to cause system crashes or potentially enable privilege escalation. The vulnerability is particularly dangerous because it occurs during error recovery mechanisms, where the system is already in an unstable state, making it more likely to trigger during actual system operation rather than controlled testing conditions.
The operational impact of this vulnerability extends beyond simple system crashes, as it can lead to complete system hangs or unexpected behavior in embedded systems and servers that rely heavily on I2C communication for hardware monitoring and control. The vulnerability was identified through automated fuzzing tools like syzbot, which repeatedly reproduced the issue by triggering the specific sequence of operations that lead to the interrupt handling error. This demonstrates that the vulnerability is not a theoretical concern but a real-world issue that can be reliably triggered under normal operating conditions. The affected systems include any Linux-based platforms using Intel 801 I2C controllers, which are commonly found in server motherboards, embedded systems, and industrial control applications where reliable I2C communication is critical for system operation.
The mitigation strategy implemented by the kernel developers involves temporarily disabling interrupts during the bus reset operation, ensuring that the interrupt handler does not receive signals during the critical reset phase. This approach follows standard practices for preventing race conditions in concurrent systems and aligns with the principles outlined in the Common Weakness Enumeration (CWE) category CWE-362, which addresses concurrent execution using lock objects. The solution also reflects techniques described in the ATT&CK framework under the T1499.004 subtechnique related to system network configuration modification, where proper handling of system-level interrupts is crucial for maintaining system stability. By disabling interrupts during the reset process and re-enabling them for subsequent transactions, the fix ensures that interrupt handling only occurs in appropriate contexts, preventing the out-of-bounds memory access that could lead to system compromise. This defensive programming approach demonstrates proper resource management and interrupt handling practices that are essential for maintaining the integrity of kernel-level drivers in modern operating systems.