Re: [PATCH 5/9] user namespace: clamp down users of cap_raised
From: Andrew G. Morgan
Date: Wed Oct 19 2011 - 00:33:30 EST
On Tue, Oct 18, 2011 at 2:54 PM, Serge Hallyn <serge@xxxxxxxxxx> wrote:
> From: "Serge E. Hallyn" <serge.hallyn@xxxxxxxxxxxxx>
>
> A few modules are using cap_raised(current_cap(), cap) to authorize
> actions. This means that tasks which are privileged in non-initial
> user namespaces will be deemed privileged. The privilege should only
> be granted if the task is in the initial user namespace.
>
> Switching the calls to capable() would change the behavior - it would
> cause the LSM capable hooks to be called, and set PF_SUPERPRIV if
> the capability was used. So instead, put in an explicit check and
> refuse privilege if the caller is not in init_user_ns.
>
> Vasiliy had suggested introducing a new helper for this. I'm open
> to suggestions, but for four callers and for a discouraged idiom,
> I'd rather not pollute the capable* function namespace with a bad name.
> (even has_capability goes through the LSM hooks)
>
> Signed-off-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxxxxx>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Andrew Morgan <morgan@xxxxxxxxxx>
> Cc: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>
> ---
> drivers/block/drbd/drbd_nl.c | 5 +++++
> drivers/md/dm-log-userspace-transfer.c | 3 +++
> drivers/staging/pohmelfs/config.c | 3 +++
> drivers/video/uvesafb.c | 3 +++
> 4 files changed, 14 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
> index 0feab26..9a87a14 100644
> --- a/drivers/block/drbd/drbd_nl.c
> +++ b/drivers/block/drbd/drbd_nl.c
> @@ -2297,6 +2297,11 @@ static void drbd_connector_callback(struct cn_msg *req, struct netlink_skb_parms
> return;
> }
>
> + if (current_user_ns() != &init_user_ns) {
I'd feel much happier with this if it did use some inline or macro here.
#define NS_IS_NON_DEFAULT (current_user_ns() != &init_user_ns)
if (NS_IS_NON_DEFAULT || !cap_raised(current_cap(), CAP_SYS_ADMIN)) {
retcode = ERR_PERM;
goto fail;
}
Is it important to support the situation that NS support is not configured?
Cheers
Andrew
> + retcode = ERR_PERM;
> + goto fail;
> + }
> +
> if (!cap_raised(current_cap(), 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..140ca81 100644
> --- a/drivers/md/dm-log-userspace-transfer.c
> +++ b/drivers/md/dm-log-userspace-transfer.c
> @@ -134,6 +134,9 @@ 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 (current_user_ns() != &init_user_ns)
> + return;
> +
> if (!cap_raised(current_cap(), CAP_SYS_ADMIN))
> return;
>
> diff --git a/drivers/staging/pohmelfs/config.c b/drivers/staging/pohmelfs/config.c
> index b6c42cb..cd259d0 100644
> --- a/drivers/staging/pohmelfs/config.c
> +++ b/drivers/staging/pohmelfs/config.c
> @@ -525,6 +525,9 @@ static void pohmelfs_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *n
> {
> int err;
>
> + if (current_user_ns() != &init_user_ns)
> + return;
> +
> if (!cap_raised(current_cap(), CAP_SYS_ADMIN))
> return;
>
> diff --git a/drivers/video/uvesafb.c b/drivers/video/uvesafb.c
> index 7f8472c..71dab8e 100644
> --- a/drivers/video/uvesafb.c
> +++ b/drivers/video/uvesafb.c
> @@ -73,6 +73,9 @@ static void uvesafb_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *ns
> struct uvesafb_task *utask;
> struct uvesafb_ktask *task;
>
> + if (current_user_ns() != &init_user_ns)
> + return;
> +
> if (!cap_raised(current_cap(), CAP_SYS_ADMIN))
> return;
>
> --
> 1.7.5.4
>
>
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