Re: [PATCH RFC 0/1] mount: universally disallow mounting over symlinks

Aleksa Sarai
2020-01-02T09:09:55Z

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On 2020-01-02, David Laight <David.Laight@ACULAB.COM> wrote:
> From: Aleksa Sarai
> > Sent: 30 December 2019 08:32
> ...
> > I'm not sure I agree -- as I mentioned in my other mail, re-opening
> > through /proc/self/fd/$n works *very* well and has for a long time (in
> > fact, both LXC and runc depend on this working).
>
> I thought it was marginally broken because it is followed as a symlink?
> On, for example, NetBSD /proc/<n>/fd/<n> is a real reference to the
> filesystem inode and can be used to link the file back into the filesystem
> if all the directory entries have been removed.

That is also the case on Linux. It (strictly speaking) isn't a symlink
in the normal sense of the word, it's a magic-link (nd_jump_link
switches the nd->path to the actual 'struct file' in the case of
/proc/self/fd/$n).

--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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