hfs: fix BUG on bnode parent update

hfs_brec_update_parent() may hit BUG_ON() if the first record of both a
leaf node and its parent are changed, and if this forces the parent to
be split. It is not possible for this to happen on a valid hfs
filesystem because the index nodes have fixed length keys.

For reasons I ignore, the hfs module does have support for a number of
hfsplus features. A corrupt btree header may report variable length
keys and trigger this BUG, so it's better to fix it.

Link: http://lkml.kernel.org/r/cf9b02d57f806[e-mail]
Signed-off-by: Ernesto A. Fernández <[e-mail]>
Reviewed-by: Andrew Morton <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Viacheslav Dubeyko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/hfs/brec.c

···
 			/* restore search_key */
 			hfs_bnode_read_key(node, fd->search_key, 14);
 		}
+		new_node = NULL;
 	}
 
 	if (!rec && node->parent)