linux-kernel - Re: [PATCH] proc connector: reject unprivileged listener bumps

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Message-ID: <20130226172441.GA6312@us.ibm.com>
Date:	Tue, 26 Feb 2013 09:24:41 -0800
From:	Matt Helsley <matthltc@...ux.vnet.ibm.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org, Evgeniy Polyakov <zbr@...emap.net>,
	netdev@...r.kernel.org, Matt Helsley <matthltc@...ibm.com>
Subject: Re: [PATCH] proc connector: reject unprivileged listener bumps

On Mon, Feb 25, 2013 at 11:32:25PM -0800, Kees Cook wrote:
> While PROC_CN_MCAST_LISTEN/IGNORE is entirely advisory, it was possible
> for an unprivileged user to turn off notifications for all listeners by
> sending PROC_CN_MCAST_IGNORE. Instead, require the same privileges as
> required for a multicast bind.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Cc: Evgeniy Polyakov <zbr@...emap.net>
> Cc: Matt Helsley <matthltc@...ibm.com>
> Cc: stable@...r.kernel.org
> ---
>  drivers/connector/cn_proc.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
> index fce2000..1110478 100644
> --- a/drivers/connector/cn_proc.c
> +++ b/drivers/connector/cn_proc.c
> @@ -313,6 +313,12 @@ static void cn_proc_mcast_ctl(struct cn_msg *msg,
>  	    (task_active_pid_ns(current) != &init_pid_ns))
>  		return;
> 
> +	/* Can only change if privileged. */

I think this comment doesn't tell us anything above and beyond the
what capability check already tells us. I think you could improve it
by noting that since the connector is multicast and not namespace-safe
it's not yet appropriate to use ns_capable() here.

Acked-by: Matt Helsley <matthltc@...ibm.com>

> +	if (!capable(CAP_NET_ADMIN)) {
> +		err = EPERM;
> +		goto out;
> +	}

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