Restrict /proc/keys such that only those keys to which the current task is
granted View permission are presented.

The documentation is also updated to reflect these changes.
Signed-off-by: NMichael LeMay <mdlemay@epoch.ncsc.mil>
Signed-off-by: NJames Morris <jmorris@namei.org>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>