Re: [PATCH RFC 1/1] mount: universally disallow mounting over symlinks

From: Andy Lutomirski
Date: Tue Jan 07 2020 - 23:39:40 EST

On Mon, Dec 30, 2019 at 12:29 AM Aleksa Sarai <cyphar@xxxxxxxxxx> wrote:
> On 2019-12-29, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > On Sun, Dec 29, 2019 at 9:21 PM Aleksa Sarai <cyphar@xxxxxxxxxx> wrote:
> If allowing bind-mounts over symlinks is allowed (which I don't have a
> problem with really), it just means we'll need a few more kernel pieces
> to get this hardening to work. But these features would be useful
> outside of the problems I'm dealing with (O_EMPTYPATH and some kind of
> pidfd-based interface to grab the equivalent of /proc/self/exe and a few
> other such magic-link targets).

As one data point, I would use this ability in virtme: this would
allow me to more reliably mount over /etc/resolve.conf even when it's
a symlink.

(Perhaps I should use overlayfs instead. Hmm.)