mm/mempolicy: fix the check of nodemask from user

mm/mempolicy: fix the check of nodemask from user

As Xiaojun reported the ltp of migrate_pages01 will fail on arm64 system
which has 4 nodes[0...3], all have memory and CONFIG_NODES_SHIFT=2:

  migrate_pages01    0  TINFO  :  test_invalid_nodes
  migrate_pages01   14  TFAIL  :  migrate_pages_common.c:45: unexpected failure - returned value = 0, expected: -1
  migrate_pages01   15  TFAIL  :  migrate_pages_common.c:55: call succeeded unexpectedly

In this case the test_invalid_nodes of migrate_pages01 will call:
SYSC_migrate_pages as:

  migrate_pages(0, , {0x0000000000000001}, 64, , {0x0000000000000010}, 64) = 0

The new nodes specifies one or more node IDs that are greater than the
maximum supported node ID, however, the errno is not set to EINVAL as
expected.

As man pages of set_mempolicy[1], mbind[2], and migrate_pages[3]
mentioned, when nodemask specifies one or more node IDs that are greater
than the maximum supported node ID, the errno should set to EINVAL.
However, get_nodes only check whether the part of bits
[BITS_PER_LONG*BITS_TO_LONGS(MAX_NUMNODES), maxnode) is zero or not, and
remain [MAX_NUMNODES, BITS_PER_LONG*BITS_TO_LONGS(MAX_NUMNODES)
unchecked.

This patch is to check the bits of [MAX_NUMNODES, maxnode) in get_nodes
to let migrate_pages set the errno to EINVAL when nodemask specifies one
or more node IDs that are greater than the maximum supported node ID,
which follows the manpage's guide.

[1] http://man7.org/linux/man-pages/man2/set_mempolicy.2.html
[2] http://man7.org/linux/man-pages/man2/mbind.2.html
[3] http://man7.org/linux/man-pages/man2/migrate_pages.2.html

Link: http://lkml.kernel.org/r/1510882624-44342-3-git-send-email-xieyisheng1@huawei.com
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Reported-by: Tan Xiaojun <tanxiaojun@huawei.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Chris Salls <salls@cs.ucsb.edu>
Cc: Christopher Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>