linux-kernel - Re: kdbus_proc_permission (Re: [GIT PULL] kdbus updates for Greg)

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Date:	Mon, 24 Aug 2015 11:52:10 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: kdbus_proc_permission (Re: [GIT PULL] kdbus updates for Greg)

Hi

On Mon, Aug 10, 2015 at 4:42 AM, Andy Lutomirski <luto@...capital.net> wrote:
> I spotted this:
>
> +/**
> + * kdbus_proc_permission() - check /proc permissions on target pid
> + * @pid_ns:            namespace we operate in
> + * @cred:              credentials of requestor
> + * @target:            target process
> + *
> + * This checks whether a process with credentials @cred can access information
> + * of @target in the namespace @pid_ns. This tries to follow /proc permissions,
> + * but is slightly more restrictive.
> + *
> + * Return: The /proc access level (KDBUS_META_PROC_*) is returned.
> + */
> +static unsigned int kdbus_proc_permission(const struct pid_namespace *pid_ns,
> +                                         const struct cred *cred,
> +                                         struct pid *target)
>
> That code ended up in a pull request, although AFAICT it was never in
> any patch email sent to me or to any public mailing list.  I suspect
> it was at least partially a response to one of my old reviews.

Exactly. It's an attempt to model metadata access similar to /proc
access (thus, access to kdbusfs implies access to procfs, but not vice
versa (nor any implication on hidepid)).

> I haven't checked the context in which it's used, but in order for
> kdbus_proc_permission to do what it claims to do, it appears to be
> missing calls to security_inode_permission and
> security_file_permission.

Both are expected to be added by lsm patches (both hooks you mentioned
are empty if no lsm is selected).

Thanks
David
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