Subject: Re: [PATCH v9 01/10] namei: obey trailing magic-link DAC permissions

From: Al Viro <[email-masked]>
Date: Fri, 12 Jul 2019 07:36:18 +0100

On Fri, Jul 12, 2019 at 05:14:54AM +0100, Al Viro wrote:

> That's not quite guaranteed (it is possible to bind a symlink on top
> of a regular file, and you will get LOOKUP_JUMPED on the entry into
> trailing_symlink() when looking the result up).  Moreover, why bother
> with LOOKUP_JUMPED here?  See that
> 	nd->last_type = LAST_BIND;
> several lines prior?  That's precisely to be able to recognize those
> suckers.

... except that this won't work these days (once upon a time it used
to, but that had been a long time ago).  However, that doesn't change
the fact that the test is really wrong.  So let's do it right:

* set a new flag along with LOOKUP_JUMPED in nd_jump_link()
* clear it in get_link() right before
	res = READ_ONCE(inode->i_link);
* check it in trailing_symlink() (or callers thereof)

The rest of comments stand, AFAICS.