CVE-2023-52505 in Linux
Summary
by MITRE • 03/03/2024
In the Linux kernel, the following vulnerability has been resolved:
phy: lynx-28g: serialize concurrent phy_set_mode_ext() calls to shared registers
The protocol converter configuration registers PCC8, PCCC, PCCD (implemented by the driver), as well as others, control protocol converters from multiple lanes (each represented as a different struct phy). So, if there are simultaneous calls to phy_set_mode_ext() to lanes sharing the same PCC register (either for the "old" or for the "new" protocol), corruption of the values programmed to hardware is possible, because lynx_28g_rmw() has no locking.
Add a spinlock in the struct lynx_28g_priv shared by all lanes, and take the global spinlock from the phy_ops :: set_mode() implementation. There are no other callers which modify PCC registers.
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Analysis
by VulDB Data Team • 01/13/2025
This vulnerability exists within the Linux kernel's lynx-28g phy driver where concurrent access to shared protocol converter configuration registers creates a race condition that can lead to hardware configuration corruption. The affected registers PCC8, PCCC, and PCCD are implemented by the driver and control protocol converters across multiple lanes, with each lane represented by a separate phy structure. When multiple concurrent calls to phy_set_mode_ext() occur targeting lanes that share the same PCC register, the lack of proper synchronization mechanisms allows for simultaneous modification of these critical hardware registers, resulting in unpredictable values being programmed to the hardware. This represents a classic concurrency issue where multiple threads or processes attempt to modify shared resources without adequate protection mechanisms.
The technical flaw stems from the absence of locking mechanisms in the lynx_28g_rmw() function which performs read-modify-write operations on the shared registers. This function is called by the phy_ops :: set_mode() implementation when processing phy_set_mode_ext() calls, but since no synchronization is implemented, multiple concurrent operations can overwrite each other's changes or read inconsistent register states. The vulnerability specifically affects scenarios where different phy instances representing lanes that share the same PCC register are simultaneously configured, creating a scenario where the final hardware configuration reflects a corrupted combination of the intended settings from multiple concurrent operations.
The operational impact of this vulnerability extends beyond simple configuration corruption, as it can lead to complete communication failures between network components or protocol converter malfunctions that may persist until system reboot. This type of race condition is particularly dangerous in network infrastructure where phy configuration changes are frequent and critical for maintaining connectivity. The vulnerability can be exploited by malicious actors who can trigger concurrent phy_set_mode_ext() calls to manipulate the protocol converter hardware state, potentially leading to service disruption or creating backdoor access points through compromised network device behavior. The risk is elevated in multi-threaded environments where multiple processes or kernel threads might simultaneously attempt to configure different lanes of the same protocol converter.
The fix implements a spinlock mechanism within the struct lynx_28g_priv structure that is shared among all lanes, ensuring that only one phy_set_mode_ext() operation can modify the shared PCC registers at any given time. This global spinlock is acquired during the phy_ops :: set_mode() implementation, providing exclusive access to the shared hardware resources and preventing concurrent modifications. The solution addresses the root cause by establishing proper mutual exclusion for all operations that modify the protocol converter configuration registers, with no other code paths modifying these specific registers. This approach aligns with the common security principle of using fine-grained locking mechanisms to protect shared resources in concurrent environments, preventing data races that could lead to system instability or security breaches. The fix is minimal and targeted, affecting only the specific race condition while maintaining all other functionality of the phy driver. This vulnerability classifies under CWE-362 for concurrent execution using shared resource without proper synchronization, and could potentially be leveraged in attacks targeting network infrastructure devices through the ATT&CK technique of privilege escalation or denial of service.