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Date:   Mon, 18 Sep 2023 15:15:18 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     Miklos Szeredi <mszeredi@redhat.com>
Cc:     Matthew House <mattlloydhouse@gmail.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-api@vger.kernel.org, linux-man@vger.kernel.org,
        linux-security-module@vger.kernel.org, Karel Zak <kzak@redhat.com>,
        Ian Kent <raven@themaw.net>,
        David Howells <dhowells@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Amir Goldstein <amir73il@gmail.com>
Subject: Re: [RFC PATCH 3/3] add listmnt(2) syscall
Message-ID: <20230918-einblick-klaut-0a010e0abc70@brauner>
References: <20230913152238.905247-1-mszeredi@redhat.com>
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 <20230917005419.397938-1-mattlloydhouse@gmail.com>
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On Sun, Sep 17, 2023 at 04:32:04PM +0200, Miklos Szeredi wrote:
> On Sun, Sep 17, 2023 at 2:54 AM Matthew House <mattlloydhouse@gmail.com> wrote:
> 
> > > +       list_for_each_entry(r, &m->mnt_mounts, mnt_child) {
> > > +               if (!capable(CAP_SYS_ADMIN) &&


> Good point.  That issue was nagging at the back of my mind.  Having an
> explicit flag nicely solves the issue.

Ideally we avoid multiple capable(CAP_SYS_ADMIN) calls by only doing it
once and saving the return value. capable() call's aren't that cheap.
Plus, we should decide whether this should trigger an audit event or
not: capable(CAP_SYS_ADMIN) triggers an audit event,
ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN) wouldn't.