CVE-2021-47436 usb: musb: dsps: Fix the probe error path

What is CVE-2021-47436?

CVE-2021-47436 is a medium-severity vulnerability in Linux kernel, published on 22 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

usb: musb: dsps: Fix the probe error path

Commit 7c75bde329d7 ("usb: musb: musb_dsps: request_irq() after initializing musb") has inverted the calls to dsps_setup_optional_vbus_irq() and dsps_create_musb_pdev() without updating correctly the error path. dsps_create_musb_pdev() allocates and registers a new platform device which must be unregistered and freed with platform_device_unregister(), and this is missing upon dsps_setup_optional_vbus_irq() error.

While on the master branch it seems not to trigger any issue, I observed a kernel crash because of a NULL pointer dereference with a v5.10.70 stable kernel where the patch mentioned above was backported. With this kernel version, -EPROBE_DEFER is returned the first time dsps_setup_optional_vbus_irq() is called which triggers the probe to error out without unregistering the platform device. Unfortunately, on the Beagle Bone Black Wireless, the platform device still living in the system is being used by the USB Ethernet gadget driver, which during the boot phase triggers the crash.

My limited knowledge of the musb world prevents me to revert this commit which was sent to silence a robot warning which, as far as I understand, does not make sense. The goal of this patch was to prevent an IRQ to fire before the platform device being registered. I think this cannot ever happen due to the fact that enabling the interrupts is done by the ->enable() callback of the platform musb device, and this platform device must be already registered in order for the core or any other user to use this callback.

Hence, I decided to fix the error path, which might prevent future errors on mainline kernels while also fixing older ones.

Weakness: CWE-476

Which versions are affected by CVE-2021-47436?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2021-47436?

Apply the vendor's patch.

Is CVE-2021-47436 being exploited?

There is no known exploitation of CVE-2021-47436 in the wild and no public exploit code.

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Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-47436, GHSA-6xwm-63wf-q2q3, UBUNTU-CVE-2021-47436.