mm: avoid null pointer access in vm_struct via /proc/vmallocinfo

mm: avoid null pointer access in vm_struct via /proc/vmallocinfo

commit f5252e009d5b87071a919221e4f6624184005368 upstream

The /proc/vmallocinfo shows information about vmalloc allocations in vmlist
that is a linklist of vm_struct. It, however, may access pages field of
vm_struct where a page was not allocated. This results in a null pointer
access and leads to a kernel panic.

Why this happen:
In __vmalloc_node() called from vmalloc(), newly allocated vm_struct
is added to vmlist at __get_vm_area_node() and then, some fields of
vm_struct such as nr_pages and pages are set at __vmalloc_area_node(). In
other words, it is added to vmlist before it is fully initialized. At the
same time, when the /proc/vmallocinfo is read, it accesses the pages field
of vm_struct according to the nr_pages field at show_numa_info(). Thus, a
null pointer access happens.

Patch:
This patch adds newly allocated vm_struct to the vmlist *after* it is fully
initialized. So, it can avoid accessing the pages field with unallocated
page when show_numa_info() is called.

Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>