staging: binder: Fix memory corruption via page aliasing

binder_deferred_release was not unmapping the page from the buffer
before freeing it, causing memory corruption.  This only happened
when page(s) had not been freed by binder_update_page_range, which
properly unmaps the pages.

This only happens on architectures with VIPT aliasing.

To reproduce, create a program which opens, mmaps, munmaps, then closes
the binder very quickly.  This should leave a page allocated when the
binder is released.  When binder_deferrred_release is called on the
close, the page will remain mapped to the address in the linear
proc->buffer.  Later, we may map the same physical page to a different
virtual address that has different coloring, and this may cause
aliasing to occur.

PAGE_POISONING will greatly increase your chances of noticing any
problems.
Signed-off-by: Christopher Lais <chris+android@zenthought.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/android/binder.c

@@ -3036,11 +3036,14 @@ static void binder_deferred_release(struct binder_proc *proc)
 		int i;
 		for (i = 0; i < proc->buffer_size / PAGE_SIZE; i++) {
 			if (proc->pages[i]) {
+				void *page_addr = proc->buffer + i * PAGE_SIZE;
 				binder_debug(BINDER_DEBUG_BUFFER_ALLOC,
 					     "binder_release: %d: "
 					     "page %d at %p not freed\n",
 					     proc->pid, i,
-					     proc->buffer + i * PAGE_SIZE);
+					     page_addr);
+				unmap_kernel_range((unsigned long)page_addr,
+					PAGE_SIZE);
 				__free_page(proc->pages[i]);
 				page_count++;
 			}