fsnotify: handle subfiles' perm events

Recently I'm working on fanotify and found the following strange
behaviors.

I wrote a program to set fanotify_mark on "/tmp/block" and FAN_DENY
all events notified.

fanotify_mask = FAN_ALL_EVENTS | FAN_ALL_PERM_EVENTS | FAN_EVENT_ON_CHILD:
$ cd /tmp/block; cat foo
cat: foo: Operation not permitted

Operation on the file is blocked as expected.

But,

fanotify_mask = FAN_ALL_PERM_EVENTS | FAN_EVENT_ON_CHILD:
$ cd /tmp/block; cat foo
aaa

It's not blocked anymore.  This is confusing behavior.  Also reading
commit "fsnotify: call fsnotify_parent in perm events", it seems like
fsnotify should handle subfiles' perm events as well as the other notify
events.

With this patch, regardless of FAN_ALL_EVENTS set or not:
$ cd /tmp/block; cat foo
cat: foo: Operation not permitted

Operation on the file is now blocked properly.

FS_OPEN_PERM and FS_ACCESS_PERM are not listed on FS_EVENTS_POSS_ON_CHILD.
 Due to fsnotify_inode_watches_children() check, if you only specify only
these events as fsnotify_mask, you don't get subfiles' perm events
notified.

This patch add the events to FS_EVENTS_POSS_ON_CHILD to get them notified
even if only these events are specified to fsnotify_mask.
Signed-off-by: Naohiro Aota <naota@elisp.net>
Cc: Eric Paris <eparis@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/fsnotify_backend.h

@@ -60,7 +60,7 @@
 #define FS_EVENTS_POSS_ON_CHILD   (FS_ACCESS | FS_MODIFY | FS_ATTRIB |\
 				   FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN |\
 				   FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE |\
-				   FS_DELETE)
+				   FS_DELETE | FS_OPEN_PERM | FS_ACCESS_PERM)
 
 #define FS_MOVE			(FS_MOVED_FROM | FS_MOVED_TO)