linux-kernel - Re: [PATCH v4 2/6] mounts: keep list of mounts in an rbtree

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Date:   Mon, 30 Oct 2023 10:06:18 +0100
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     Ian Kent <raven@...maw.net>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-man@...r.kernel.org,
        linux-security-module@...r.kernel.org, Karel Zak <kzak@...hat.com>,
        David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Amir Goldstein <amir73il@...il.com>,
        Matthew House <mattlloydhouse@...il.com>,
        Florian Weimer <fweimer@...hat.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v4 2/6] mounts: keep list of mounts in an rbtree

On Mon, Oct 30, 2023 at 6:45 AM Ian Kent <raven@...maw.net> wrote:

> Is fs/namespace.c:iterate_mounts() a problem?
>
> It's called from:
>
> 1) ./kernel/audit_tree.c:709: if (iterate_mounts(compare_root,
> 2) ./kernel/audit_tree.c:839:    err = iterate_mounts(tag_mount, tree, mnt);
> 3) ./kernel/audit_tree.c:917:        failed = iterate_mounts(tag_mount,
> tree, tagged);
>
>
>  From functions 1) audit_trim_trees(), 2) audit_add_tree_rule() and
>
> 3) audit_tag_tree().

So that interface works like this:

 - collect_mounts() creates a temporary copy of a mount tree, mounts
are chained on mnt_list.

 - iterate_mounts() is used to do some work on the temporary tree

 - drop_collected_mounts() frees the temporary tree

These mounts are never installed in a namespace.  My guess is that a
private copy is used instead of the original mount tree to prevent
races.

Thanks,
Miklos