CVE-2022-50240

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]

Red Hat Enterprise Linux is not affected by this vulnerability because the Android Binder IPC driver is not enabled in supported Red Hat kernels. The flaw stems from a memory management race condition within the Android Binder subsystem when deallocating virtual memory areas, which could lead to a use-after-free scenario. Because this driver is not compiled into Red Hat enterprise kernel packages, systems running Red Hat Enterprise Linux are not exposed to this issue.