On Tue, Feb 16, 2021 at 06:00:34PM +0000, Al Viro wrote:

Sigh...  OK, so we want something like
	user_path_create()
	vfs_mknod()
	created = true
	grab bindlock
	....
	drop bindlock
	if failed && created
		vfs_unlink()
	done_path_create()	
in unix_bind()...  That would push ->bindlock all way down in the hierarchy,
so that should be deadlock-free, but it looks like that'll be fucking ugly ;-/

Let me try and play with that a bit, maybe it can be massaged to something
relatively sane...

OK...  Completely untested series follows.  Preliminary massage in first
6 patches, then actual "add cleanup on failure", then minor followup
cleanup.
      af_unix: take address assignment/hash insertion into a new helper
      unix_bind(): allocate addr earlier
      unix_bind(): separate BSD and abstract cases
      unix_bind(): take BSD and abstract address cases into new helpers
      fold unix_mknod() into unix_bind_bsd()
      unix_bind_bsd(): move done_path_create() call after dealing with ->bindlock
      unix_bind_bsd(): unlink if we fail after successful mknod
      __unix_find_socket_byname(): don't pass hash and type separately

Branch is in git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #misc.af_unix,
individual patches in followups