ceph: avoid use-after-free in ceph_fl_release_lock()

When ceph releasing the file_lock it will try to get the inode pointer
from the fl->fl_file, which the memory could already be released by
another thread in filp_close(). Because in VFS layer the fl->fl_file
doesn't increase the file's reference counter.

Will switch to use ceph dedicate lock info to track the inode.

And in ceph_fl_release_lock() we should skip all the operations if the
fl->fl_u.ceph.inode is not set, which should come from the request
file_lock. And we will set fl->fl_u.ceph.inode when inserting it to the
inode lock list, which is when copying the lock.

Link: https://tracker.ceph.com/issues/57986
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

include/linux/fs.h

@@ -1119,6 +1119,9 @@ struct file_lock {
 			int state;		/* state of grant or error if -ve */
 			unsigned int	debug_id;
 		} afs;
+		struct {
+			struct inode *inode;
+		} ceph;
 	} fl_u;
 } __randomize_layout;