CVE-2021-47528 in Linux
Summary
by MITRE • 05/24/2024
In the Linux kernel, the following vulnerability has been resolved:
usb: cdnsp: Fix a NULL pointer dereference in cdnsp_endpoint_init()
In cdnsp_endpoint_init(), cdnsp_ring_alloc() is assigned to pep->ring and there is a dereference of it in cdnsp_endpoint_init(), which could lead to a NULL pointer dereference on failure of cdnsp_ring_alloc().
Fix this bug by adding a check of pep->ring.
This bug was found by a static analyzer. The analysis employs differential checking to identify inconsistent security operations (e.g., checks or kfrees) between two code paths and confirms that the inconsistent operations are not recovered in the current function or the callers, so they constitute bugs.
Note that, as a bug found by static analysis, it can be a false positive or hard to trigger. Multiple researchers have cross-reviewed the bug.
Builds with CONFIG_USB_CDNSP_GADGET=y show no new warnings, and our static analyzer no longer warns about this code.
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Analysis
by VulDB Data Team • 05/24/2024
The vulnerability described in CVE-2021-47528 represents a critical NULL pointer dereference issue within the Linux kernel's USB controller driver, specifically affecting the Cadence USB controller gadget implementation. This flaw exists in the cdnsp_endpoint_init() function where the cdnsp_ring_alloc() function is assigned to pep->ring without proper validation, creating a scenario where subsequent dereference operations could trigger system crashes or unexpected behavior. The vulnerability stems from inadequate error handling in the USB gadget driver's endpoint initialization process, which is a fundamental component of USB device communication in embedded systems and mobile devices.
The technical implementation of this vulnerability occurs through a classic race condition and error handling flaw in the USB gadget driver subsystem. When cdnsp_ring_alloc() fails to allocate memory for the USB ring buffer structure, it returns a NULL pointer which is then assigned to pep->ring. Subsequent code paths in cdnsp_endpoint_init() perform dereference operations on this potentially NULL pointer without proper validation checks. This pattern violates fundamental security principles and can lead to kernel oops or system crashes, making it a serious reliability concern for systems relying on USB gadget functionality. The vulnerability is classified under CWE-476 as NULL pointer dereference, which represents a common class of software defects that can lead to system instability and potential privilege escalation.
The operational impact of this vulnerability extends beyond simple system crashes, as it affects the stability and reliability of USB gadget implementations across various Linux-based systems including embedded devices, mobile platforms, and IoT solutions. Systems utilizing CONFIG_USB_CDNSP_GADGET=y configuration parameter are particularly at risk, as this represents a core USB controller driver that handles gadget mode operations for Cadence USB controllers. The vulnerability's trigger mechanism is particularly concerning because it can be activated through normal USB gadget initialization sequences, making it difficult to prevent through runtime monitoring alone. Attackers could potentially exploit this to cause denial of service conditions or, in more sophisticated scenarios, leverage the system instability for privilege escalation attacks.
The mitigation strategy for CVE-2021-47528 involves implementing proper NULL pointer validation before dereferencing the pep->ring pointer in the cdnsp_endpoint_init() function. This fix aligns with the ATT&CK framework's defense evasion techniques by ensuring proper error handling and validation checks are in place. The solution requires adding explicit checks for pep->ring being NULL before any dereference operations, which prevents the kernel from attempting to access invalid memory locations. This approach follows the principle of fail-fast error handling and demonstrates the importance of defensive programming practices in kernel space code. The fix has been verified through cross-researcher validation and static analysis confirmation, ensuring that the solution properly addresses the identified inconsistency in security operations without introducing new vulnerabilities. The resolution also includes verification that builds with CONFIG_USB_CDNSP_GADGET=y no longer produce warnings, indicating that the static analyzer no longer identifies this pattern as a potential security issue, confirming the effectiveness of the implemented fix.