Re: [PATCH] userns: Replace netlink uses of cap_raised with capable.

Serge E. Hallyn
2012-04-04T02:26:36Z

Quoting Eric W. Biederman (ebiederm@xmission.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@trash.net>
> Cc: Philipp Reisner <philipp.reisner@linbit.com>
> Cc: Serge E. Hallyn <serge.hallyn@canonical.com>

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

thanks,
-serge

> Cc: Andrew Morgan <morgan@kernel.org>
> Cc: Vasiliy Kulikov <segoon@openwall.com>
> Cc: David Howells <dhowells@redhat.com>
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.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