linux-kernel - Re: [PATCH 04/24] VFS: Add LSM hooks for filesystem context [ver #7]

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Date:   Tue, 24 Apr 2018 16:22:47 +0100
From:   David Howells <dhowells@...hat.com>
To:     Stephen Smalley <sds@...ho.nsa.gov>
Cc:     dhowells@...hat.com, Paul Moore <paul@...l-moore.com>,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, viro@...iv.linux.org.uk,
        selinux@...ho.nsa.gov, linux-fsdevel@...r.kernel.org,
        linux-afs@...ts.infradead.org
Subject: Re: [PATCH 04/24] VFS: Add LSM hooks for filesystem context [ver #7]

Stephen Smalley <sds@...ho.nsa.gov> wrote:

> Neither fsopen() nor fscontext_fs_write() appear to perform any kind of
> up-front permission checking (DAC or MAC), although some security hooks may
> be ultimately called to allocate structures, parse security options, etc.
> Is there a reason not apply a may_mount() or similar check up front?

may_mount() is called by fsmount() at the moment.  It may make sense to move
this earlier to fsopen().  Note that there's also going to be something that
looks like:

	fd = fspick("/mnt");
	fsmount(fd, "/a", MNT_NOEXEC); // ie. bind mount

or:

	fd = fspick("/mnt");
	write(fd, "o intr");
	write(fd, "x reconfigure"); // ie. something like remount
	close(fd);

I guess we'd want to call may_mount() in fspick() too.  But there's also the
possibility of using this to create a query interfact too:

	fd = fspick("/mnt");
	write(fd, "q intr");
	read(fd, value_buffer);

David