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 binderalloc struct to record the start address of the VMA and use vmalookup() to get the vma when needed. Add lockdep mmaplock 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 smpwmb()/smp_rmb() was not necessary.

[akpm@linux-foundation.org: fix drivers/android/binderallocselftest.c]