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CVE-2021-47436

Disclosure Date: May 22, 2024 •
CVE-2021-47436
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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.

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CVSS V3 Severity and Metrics
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General Information

Offensive Application
Unknown
Utility Class
Unknown
Ports
Unknown
OS
Unknown
Vulnerable Versions
Linux 5ed60a430fb5
Linux e923bce31ffe
Linux 9ab5d539bc97
Linux 9d89e2871167
Linux ff9249aab398
Linux c2115b2b1642
Linux 4.14.252
Linux 4.19.213
Linux 5.4.155
Linux 5.10.75
Linux 5.14.14
Prerequisites
Unknown
Discovered By
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PoC Author
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Metasploit Module
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Reporter
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Vendors

  • Linux

Products

  • Linux
Technical Analysis