CVE-2022-50128 in Linux
Summary
by MITRE • 06/18/2025
In the Linux kernel, the following vulnerability has been resolved:
android: binder: stop saving a pointer to the VMA
Do not record a pointer to a VMA outside of the mmap_lock for later use. This is unsafe and there are a number of failure paths *after* the recorded VMA pointer may be freed during setup. There is no callback to the driver to clear the saved pointer from generic mm code. Furthermore, the VMA pointer may become stale if any number of VMA operations end up freeing the VMA so saving it was fragile to being with.
Instead, change the binder_alloc struct to record the start address of the VMA and use vma_lookup() to get the vma when needed. Add lockdep mmap_lock checks on updates to the vma pointer to ensure the lock is held and depend on that lock for synchronization of readers and writers - which was already the case anyways, so the smp_wmb()/smp_rmb() was not necessary.
[[email protected]: fix drivers/android/binder_alloc_selftest.c]
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Analysis
by VulDB Data Team • 12/01/2025
The vulnerability CVE-2022-50128 addresses a critical memory management issue within the Linux kernel's android binder driver implementation. This flaw exists in the binder_alloc subsystem which handles memory allocation for inter-process communication in Android systems. The vulnerability stems from improper handling of Virtual Memory Area (VMA) pointers during memory mapping operations, creating a potential race condition that could lead to use-after-free conditions and arbitrary code execution. The issue specifically affects systems using the android binder interface for process communication, particularly those running kernel versions where this particular memory management flaw was present.
The technical root cause involves the binder driver's attempt to cache VMA pointers for performance optimization purposes. When the driver saves a pointer to a VMA structure outside of the mmap_lock critical section, it creates a dangerous scenario where the cached pointer may become invalid if the VMA gets freed during subsequent operations. This pattern violates fundamental memory safety principles and creates multiple failure paths where the saved pointer reference could point to freed memory. The vulnerability is classified under CWE-415 as Double Free and CWE-416 as Use After Free, representing classic memory corruption vulnerabilities that can be exploited for privilege escalation or system compromise. The kernel's memory management subsystem relies on proper locking mechanisms to ensure VMA integrity, but the flawed implementation bypassed these safeguards by storing pointers outside the appropriate synchronization context.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a fundamental flaw in the kernel's memory management architecture that could enable attackers to execute arbitrary code with kernel privileges. When the binder driver attempts to access a stale VMA pointer, the system may experience kernel crashes or more critically, allow attackers to manipulate memory contents through controlled pointer dereferences. This vulnerability affects Android-based systems that utilize the binder IPC mechanism, potentially compromising the security boundary between user-space applications and kernel-space operations. The flaw demonstrates the importance of proper lock ordering and memory management practices in kernel code, as highlighted by ATT&CK technique T1068 which covers Local Privilege Escalation through kernel exploits.
The fix implemented addresses the core issue by changing the binder_alloc structure to store only the VMA start address rather than a direct pointer reference. This approach eliminates the race condition by requiring that VMA information be retrieved on-demand using the established vma_lookup() function, which properly handles the mmap_lock synchronization. The solution incorporates lockdep mmap_lock checks to ensure proper locking protocols are maintained during VMA pointer updates, reinforcing the existing synchronization mechanisms that were already in place. This approach removes the need for explicit memory barriers (smp_wmb()/smp_rmb()) that were previously used to manage memory ordering but were unnecessary given the proper lock-based synchronization. The fix also includes modifications to the self-test code to ensure that the corrected implementation maintains proper functionality while eliminating the vulnerability. The resolution follows established kernel security practices and demonstrates the importance of maintaining proper locking semantics in kernel memory management subsystems, particularly in driver code that handles sensitive inter-process communication mechanisms.