linux-kernel - Re: [PATCH] userns: Replace netlink uses of cap

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Date:	Wed, 4 Apr 2012 02:26:52 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Philipp Reisner <philipp.reisner@...bit.com>,
	Patrick McHardy <kaber@...sh.net>,
	Andrew Morgan <morgan@...nel.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	David Howells <dhowells@...hat.com>,
	Neil Brown <neilb@...e.de>,
	Michal Januszewski <spock@...too.org>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-fbdev@...r.kernel.org,
	linux-raid@...r.kernel.org
Subject: Re: [PATCH] userns: Replace netlink uses of cap_raised with
 capable.

Quoting Eric W. Biederman (ebiederm@...ssion.com):
> 
> In 2009 Philip Reiser notied that a few users of netlink connector
> interface needed a capability check and added the idiom
> cap_raised(nsp->eff_cap, CAP_SYS_ADMIN) to a few of them, on the premise
> that netlink was asynchronous.
> 
> In 2011 Patrick McHardy noticed we were being silly because netlink is
> synchronous and removed eff_cap from the netlink_skb_params and changed
> the idiom to cap_raised(current_cap(), CAP_SYS_ADMIN).
> 
> Looking at those spots with a fresh eye we should be calling
> capable(CAP_SYS_ADMIN).  The only reason I can see for not calling
> capable is that it once appeared we were not in the same task as the
> caller which would have made calling capable() impossible.

And (just to make sure) that is now absolutely not the case?

> In the initial user_namespace the only difference between  between
> cap_raised(current_cap(), CAP_SYS_ADMIN) and capable(CAP_SYS_ADMIN)
> are a few sanity checks and the fact that capable(CAP_SYS_ADMIN)
> sets PF_SUPERPRIV if we use the capability.
> 
> Since we are going to be using root privilege setting PF_SUPERPRIV
> seems the right thing to do.
> 
> The motivation for this that patch is that in a child user namespace
> cap_raised(current_cap(),...) tests your capabilities with respect to
> that child user namespace not capabilities in the initial user namespace
> and thus will allow processes that should be unprivielged to use the
> kernel services that are only protected with
> cap_raised(current_cap(),..).
> 
> To fix possible user_namespace issues and to just clean up the code
> replace cap_raised(current_cap(), CAP_SYS_ADMIN) with
> capable(CAP_SYS_ADMIN).
> 
> Cc: Patrick McHardy <kaber@...sh.net>
> Cc: Philipp Reisner <philipp.reisner@...bit.com>
> Cc: Serge E. Hallyn <serge.hallyn@...onical.com>

Acked-by: Serge E. Hallyn <serge.hallyn@...onical.com>

thanks,
-serge

> Cc: Andrew Morgan <morgan@...nel.org>
> Cc: Vasiliy Kulikov <segoon@...nwall.com>
> Cc: David Howells <dhowells@...hat.com>
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> ---
>  drivers/block/drbd/drbd_nl.c           |    2 +-
>  drivers/md/dm-log-userspace-transfer.c |    2 +-
>  drivers/video/uvesafb.c                |    2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
> index abfaaca..946166e 100644
> --- a/drivers/block/drbd/drbd_nl.c
> +++ b/drivers/block/drbd/drbd_nl.c
> @@ -2297,7 +2297,7 @@ static void drbd_connector_callback(struct cn_msg *req, struct netlink_skb_parms
>  		return;
>  	}
>  
> -	if (!cap_raised(current_cap(), CAP_SYS_ADMIN)) {
> +	if (!capable(CAP_SYS_ADMIN)) {
>  		retcode = ERR_PERM;
>  		goto fail;
>  	}
> diff --git a/drivers/md/dm-log-userspace-transfer.c b/drivers/md/dm-log-userspace-transfer.c
> index 1f23e04..08d9a20 100644
> --- a/drivers/md/dm-log-userspace-transfer.c
> +++ b/drivers/md/dm-log-userspace-transfer.c
> @@ -134,7 +134,7 @@ static void cn_ulog_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
>  {
>  	struct dm_ulog_request *tfr = (struct dm_ulog_request *)(msg + 1);
>  
> -	if (!cap_raised(current_cap(), CAP_SYS_ADMIN))
> +	if (!capable(CAP_SYS_ADMIN))
>  		return;
>  
>  	spin_lock(&receiving_list_lock);
> diff --git a/drivers/video/uvesafb.c b/drivers/video/uvesafb.c
> index 260cca7..9f7d27a 100644
> --- a/drivers/video/uvesafb.c
> +++ b/drivers/video/uvesafb.c
> @@ -73,7 +73,7 @@ static void uvesafb_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *ns
>  	struct uvesafb_task *utask;
>  	struct uvesafb_ktask *task;
>  
> -	if (!cap_raised(current_cap(), CAP_SYS_ADMIN))
> +	if (!capable(CAP_SYS_ADMIN))
>  		return;
>  
>  	if (msg->seq >= UVESAFB_TASKS_MAX)
> -- 
> 1.7.2.5
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