CVE-2022-48815 in Linux
Summary
by MITRE • 07/16/2024
In the Linux kernel, the following vulnerability has been resolved:
net: dsa: bcm_sf2: don't use devres for mdiobus
As explained in commits: 74b6d7d13307 ("net: dsa: realtek: register the MDIO bus under devres") 5135e96a3dd2 ("net: dsa: don't allocate the slave_mii_bus using devres")
mdiobus_free() will panic when called from devm_mdiobus_free() <- devres_release_all() <- __device_release_driver(), and that mdiobus was not previously unregistered.
The Starfighter 2 is a platform device, so the initial set of constraints that I thought would cause this (I2C or SPI buses which call ->remove on ->shutdown) do not apply. But there is one more which applies here.
If the DSA master itself is on a bus that calls ->remove from ->shutdown (like dpaa2-eth, which is on the fsl-mc bus), there is a device link between the switch and the DSA master, and device_links_unbind_consumers() will unbind the bcm_sf2 switch driver on shutdown.
So the same treatment must be applied to all DSA switch drivers, which is: either use devres for both the mdiobus allocation and registration, or don't use devres at all.
The bcm_sf2 driver has the code structure in place for orderly mdiobus removal, so just replace devm_mdiobus_alloc() with the non-devres variant, and add manual free where necessary, to ensure that we don't let devres free a still-registered bus.
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Analysis
by VulDB Data Team • 10/06/2025
The vulnerability identified as CVE-2022-48815 affects the Linux kernel's Distributed Switch Architecture implementation specifically within the bcm_sf2 driver used for Starfighter 2 platform devices. This issue stems from improper management of MDIO bus resources during device shutdown sequences, creating a potential system panic condition that could compromise network connectivity and system stability. The problem manifests when the device resource management subsystem attempts to free MDIO bus resources through devm_mdiobus_free() during driver shutdown, but encounters a previously registered bus that has not been properly unregistered.
The technical flaw originates from inconsistent resource management patterns within the DSA subsystem where some drivers use device resource management (devres) for MDIO bus allocation while others do not. When the bcm_sf2 driver employs devm_mdiobus_alloc() for MDIO bus allocation, it creates a conflict with the device shutdown sequence. During shutdown, if the DSA master device resides on a bus that invokes ->remove from ->shutdown operations, device links trigger unbinding of the bcm_sf2 switch driver through device_links_unbind_consumers(). This sequence leads to a race condition where devres attempts to free the MDIO bus while it remains registered, causing a kernel panic through the mdiobus_free() function call.
This vulnerability specifically impacts systems utilizing the bcm_sf2 DSA switch driver on platforms where the DSA master operates on buses that perform shutdown cleanup operations such as the fsl-mc bus used by dpaa2-eth drivers. The issue affects the broader DSA switch driver ecosystem as the same resource management inconsistency exists across multiple switch drivers in the kernel. The problem is categorized under CWE-415: Double Free and CWE-416: Use After Free, as it involves improper resource lifecycle management during device shutdown operations. The attack surface is primarily limited to kernel-level operations during system shutdown or device removal scenarios, making it a critical issue for embedded systems and network infrastructure devices that rely on DSA for switch management.
The operational impact of this vulnerability extends beyond simple system crashes to potentially disrupt network services and device functionality during normal shutdown procedures. Systems using affected bcm_sf2 drivers may experience kernel panics when devices are powered down or removed, leading to service interruptions and potential data loss. The vulnerability is particularly concerning for network equipment and embedded systems that require stable operation during power management events, as it directly affects the reliability of network switch operations during shutdown sequences. Organizations running Linux-based network infrastructure must address this issue to maintain system stability and prevent unexpected service disruptions.
The recommended mitigation strategy involves modifying the bcm_sf2 driver to consistently use either devres for both allocation and registration of MDIO buses or avoid devres entirely for MDIO bus management. The solution requires replacing devm_mdiobus_alloc() with the standard non-devres variant and implementing manual resource cleanup to ensure proper MDIO bus unregistration before attempting resource deallocation. This approach aligns with ATT&CK technique T1566.001: Phishing: Spearphishing Attachment, as it addresses a kernel-level vulnerability that could be exploited to cause system instability, though the actual exploitation would require specific conditions related to device shutdown sequences. The fix pattern established here should be applied to all DSA switch drivers to prevent similar issues across the kernel's DSA implementation, ensuring consistent resource management practices throughout the network switch subsystem.