linux-kernel - RE: [PATCH RFC 0/1] mount: universally disallow mounting over symlinks

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Message-ID: <e1066da936244de99e7ee827695d6583@AcuMS.aculab.com>
Date:   Thu, 2 Jan 2020 08:58:09 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Aleksa Sarai' <cyphar@...har.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        stable <stable@...r.kernel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Serge Hallyn <serge@...lyn.com>,
        "dev@...ncontainers.org" <dev@...ncontainers.org>,
        "Linux Containers" <containers@...ts.linux-foundation.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RFC 0/1] mount: universally disallow mounting over
 symlinks

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.

	David

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