linux-ext4 - Re: [PATCH v5 10/42] capability: handle idmapped mounts

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Message-ID: <20210119092209.GB3361757@infradead.org>
Date:   Tue, 19 Jan 2021 09:22:09 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org,
        John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Geoffrey Thomas <geofft@...reload.com>,
        Mrunal Patel <mpatel@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Andy Lutomirski <luto@...nel.org>,
        Theodore Tso <tytso@....edu>, Alban Crequy <alban@...volk.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Howells <dhowells@...hat.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        St??phane Graber <stgraber@...ntu.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Lennart Poettering <lennart@...ttering.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, smbarber@...omium.org,
        Phil Estes <estesp@...il.com>, Serge Hallyn <serge@...lyn.com>,
        Kees Cook <keescook@...omium.org>,
        Todd Kjos <tkjos@...gle.com>, Paul Moore <paul@...l-moore.com>,
        Jonathan Corbet <corbet@....net>,
        containers@...ts.linux-foundation.org,
        linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v5 10/42] capability: handle idmapped mounts

On Tue, Jan 12, 2021 at 11:00:52PM +0100, Christian Brauner wrote:
> In order to determine whether a caller holds privilege over a given
> inode the capability framework exposes the two helpers
> privileged_wrt_inode_uidgid() and capable_wrt_inode_uidgid(). The former
> verifies that the inode has a mapping in the caller's user namespace and
> the latter additionally verifies that the caller has the requested
> capability in their current user namespace.
> If the inode is accessed through an idmapped mount we simply need to map
> it according to the mount's user namespace. Afterwards the checks are
> identical to non-idmapped inodes. If the initial user namespace is
> passed all operations are a nop so non-idmapped mounts will not see a
> change in behavior and will also not see any performance impact.

This adds a bunch of pointless > 80 char lines, that would be nice to
fix up.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@....de>