CVE-2022-50240

/// Technical description

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]

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References