CVE-2021-47436: 
Linux Kernel vulnerability analysis and mitigation

In the Linux kernel, CVE-2021-47436 addresses a vulnerability in the USB MUSB DSPS driver. The issue was introduced by commit 7c75bde329d7 which inverted the calls to dsps_setup_optional_vbus_irq() and dsps_create_musb_pdev() without properly updating the error path. The vulnerability was discovered in 2021 and affects the Linux kernel's USB subsystem (Kernel Git).

The vulnerability stems from a missing platform_device_unregister() call in the error path when dsps_create_musb_pdev() allocates and registers a new platform device. When dsps_setup_optional_vbus_irq() fails, the platform device remains registered without proper cleanup. This becomes particularly problematic when -EPROBE_DEFER is returned during the first call to dsps_setup_optional_vbus_irq(), causing the probe to fail without unregistering the platform device (Kernel Git).

The vulnerability can lead to a kernel crash due to NULL pointer dereference. This was observed specifically on the Beagle Bone Black Wireless platform, where the unfreed platform device is accessed by the USB Ethernet gadget driver during the boot phase, triggering a system crash (Kernel Git).

The vulnerability is triggered during system initialization when specific conditions are met, particularly on systems using the affected USB MUSB DSPS driver. It requires no special privileges to trigger, as it occurs during the normal boot process when the USB subsystem is initialized (Kernel Git).

The issue has been fixed by adding proper cleanup in the error path. The fix adds an unregister_pdev label and ensures platform_device_unregister() is called when dsps_setup_optional_vbus_irq() fails. Users should update to a patched kernel version that includes the fix (Kernel Git).