linux-kernel - Re: [RFC PATCH 3/3] add listmnt(2) syscall

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Message-ID: <CAJfpegtJwcS9=7dCAVCEoBwD_U2MX44a6B62iDsc78AZt6nM7Q@mail.gmail.com>
Date:   Thu, 28 Sep 2023 12:07:17 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Christian Brauner <brauner@...nel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Matthew House <mattlloydhouse@...il.com>,
        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>,
        Ian Kent <raven@...maw.net>,
        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>
Subject: Re: [RFC PATCH 3/3] add listmnt(2) syscall

On Tue, 19 Sept 2023 at 18:48, Paul Moore <paul@...l-moore.com> wrote:

> > 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.
>
> Agreed.  The capability check doesn't do any subject/object
> comparisons so calling it for each mount is overkill.  However, I
> would think we would want the LSM hook called from inside the loop as
> that could involve a subject (@current) and object (individual mount
> point) comparison.

The security_sb_statfs() one?

Should a single failure result in a complete failure?

Why is it not enough to check permission on the parent?

Thanks,
Miklos