vmcore: fix PT_NOTE n_namesz, n_descsz overflow issue

vmcore: fix PT_NOTE n_namesz, n_descsz overflow issue

When updating PT_NOTE header size (ie.  p_memsz), an overflow issue
happens with the following bogus note entry:

  n_namesz = 0xFFFFFFFF
  n_descsz = 0x0
  n_type   = 0x0

This kind of note entry should be dropped during updating p_memsz.  But
because n_namesz is 32bit, after (n_namesz + 3) & (~3), it's overflow to
0x0, the note entry size looks sane and reserved.

When userspace (eg.  crash utility) is trying to access such bogus note,
it could lead to an unexpected behavior (eg.  crash utility segment fault
because it's reading bogus address).

The source of bogus note hasn't been identified yet.  At least we could
drop the bogus note so user space wouldn't be surprised.

Signed-off-by: WANG Chao <chaowang@redhat.com>
Cc: Dave Anderson <anderson@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Randy Wright <rwright@hp.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Rashika Kheria <rashika.kheria@gmail.com>
Cc: Greg Pearson <greg.pearson@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>