CVE-2022-48941 in Linux
Summary
by MITRE • 08/22/2024
In the Linux kernel, the following vulnerability has been resolved:
ice: fix concurrent reset and removal of VFs
Commit c503e63200c6 ("ice: Stop processing VF messages during teardown") introduced a driver state flag, ICE_VF_DEINIT_IN_PROGRESS, which is intended to prevent some issues with concurrently handling messages from VFs while tearing down the VFs.
This change was motivated by crashes caused while tearing down and bringing up VFs in rapid succession.
It turns out that the fix actually introduces issues with the VF driver caused because the PF no longer responds to any messages sent by the VF during its .remove routine. This results in the VF potentially removing its DMA memory before the PF has shut down the device queues.
Additionally, the fix doesn't actually resolve concurrency issues within the ice driver. It is possible for a VF to initiate a reset just prior to the ice driver removing VFs. This can result in the remove task concurrently operating while the VF is being reset. This results in similar memory corruption and panics purportedly fixed by that commit.
Fix this concurrency at its root by protecting both the reset and removal flows using the existing VF cfg_lock. This ensures that we cannot remove the VF while any outstanding critical tasks such as a virtchnl message or a reset are occurring.
This locking change also fixes the root cause originally fixed by commit c503e63200c6 ("ice: Stop processing VF messages during teardown"), so we can simply revert it.
Note that I kept these two changes together because simply reverting the original commit alone would leave the driver vulnerable to worse race conditions.
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Analysis
by VulDB Data Team • 08/23/2024
The vulnerability described in CVE-2022-48941 affects the linux kernel's ice driver which manages Intel Ethernet network adapters. This issue stems from improper handling of concurrent operations during virtual function (VF) reset and removal processes, creating a race condition that can lead to system instability and potential memory corruption. The problem manifests when the physical function (PF) attempts to tear down VFs while VF messages are still being processed, creating a scenario where the driver's state management becomes inconsistent.
The root cause of this vulnerability lies in the introduction of the ICE_VF_DEINIT_IN_PROGRESS flag through commit c503e63200c6, which was intended to address crashes occurring during rapid VF teardown and reinitialization cycles. However, this fix inadvertently created new problems by preventing the PF from responding to VF messages during the removal process, specifically during the .remove routine execution. This prevents proper cleanup of DMA memory allocation, as the VF may attempt to free its memory resources before the PF has properly shut down device queues, leading to potential memory corruption scenarios.
The technical flaw represents a concurrency issue that violates fundamental principles of concurrent programming and system state management. The fix addresses this by implementing proper locking mechanisms using the existing VF cfg_lock to protect both reset and removal operations simultaneously. This approach ensures that VF removal cannot occur while critical tasks such as virtchnl messages or resets are in progress, thereby preventing the race conditions that could lead to memory corruption and system panics.
This vulnerability has significant operational impact on systems utilizing Intel Ethernet adapters in virtualized environments where VFs are frequently reset or removed. The concurrency issues can result in system crashes, data corruption, and potential denial of service conditions that affect network connectivity and overall system stability. The fix addresses the fundamental race condition rather than merely masking symptoms, which aligns with security best practices for preventing similar issues in complex multi-threaded driver environments.
From a cybersecurity perspective, this vulnerability demonstrates the importance of proper synchronization mechanisms in kernel drivers and highlights how seemingly beneficial fixes can introduce new security weaknesses. The issue relates to CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and can be mapped to ATT&CK techniques involving privilege escalation through kernel exploits or system stability compromise. The solution demonstrates proper defensive programming principles by using existing synchronization primitives rather than introducing new, potentially error-prone mechanisms. The fix also shows the importance of thorough testing in concurrent environments and the need for comprehensive validation of changes that affect critical system components.