Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks and file bind mounts (try #5)

Pavel Machek
2009-11-30T12:28:54Z

On Tue 2009-11-24 13:59:06, Miklos Szeredi wrote:
> On Tue, 24 Nov 2009, Pavel Machek wrote:
> > I believe that current semantics is ugly enough that 'documenting' it
> > is not enough... and people want to port from other systems, too, not
> > expecting nasty surprises like this...
>
> This hasn't been a problem for the last 12 years, and still we don't
> see script kiddies exploiting this hole and sysadmins hurrying to
> secure their system, even though it has been public for quite a while.
>
> Why?

Because condition when it hits are quite unusual?

> The reason might be, that there *is no* violation of security.

Well, security people disagree with you.

> See this: the surprise isn't that an inode can be reached from
> multiple paths, that has been possible with hard links for as long as
> unix lived. The suprise is that the inode can be reached through
> proc. So this "hole" that has been opened about 12 years ago in linux
> is quite well known. Only this particular aspect of it isn't well
> known, but that doesn't mean it's not right, does it?

It does. Bypassing checks on read-only file descriptors is design
misfeature, and users are clearly unaware. (See bugtraq). Being "old"
does not mean it is right.
Pavel
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