linux-kernel - Re: [PATCH 05/10] user namespace: clamp down users of cap

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Message-ID: <CALQRfL4zCbzr_Fa0ySi96j06nw7ifocCxUjYUs6vXxeNvjCutQ@mail.gmail.com>
Date:	Mon, 24 Oct 2011 08:47:01 -0700
From:	"Andrew G. Morgan" <morgan@...nel.org>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	David Howells <dhowells@...hat.com>, linux-kernel@...r.kernel.org,
	ebiederm@...ssion.com, akpm@...ux-foundation.org, oleg@...hat.com,
	richard@....at, mikevs@...all.net, segoon@...nwall.com,
	gregkh@...e.de, eparis@...hat.com,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>
Subject: Re: [PATCH 05/10] user namespace: clamp down users of cap_raised

Serge,

It seems as if this whole thing is really idiomatic. How about?

#define IN_ROOT_USER_NS_CAPABLE(cap)  \
   ((current_user_ns() == &init_user_ns) && cap_raised(current_cap(), cap))

Cheers

Andrew

On Mon, Oct 24, 2011 at 7:43 AM, Serge E. Hallyn <serge@...lyn.com> wrote:
> 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.
>
> Changelog:
> Oct 23: Use a nice macro to make the code shorter and easier to read,
>        per advice from Andrew Morgan and David Howells.
>
> Signed-off-by: Serge E. Hallyn <serge.hallyn@...onical.com>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: Andrew Morgan <morgan@...nel.org>
> Cc: Vasiliy Kulikov <segoon@...nwall.com>
> Cc: David Howells <dhowells@...hat.com>
> ---
>  drivers/block/drbd/drbd_nl.c           |    2 +-
>  drivers/md/dm-log-userspace-transfer.c |    2 +-
>  drivers/staging/pohmelfs/config.c      |    2 +-
>  drivers/video/uvesafb.c                |    2 +-
>  include/linux/cred.h                   |    2 ++
>  5 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
> index 0feab26..f799b15 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 (!IN_ROOT_USER_NS() || !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..126a79b 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 (!IN_ROOT_USER_NS() || !cap_raised(current_cap(), CAP_SYS_ADMIN))
>                return;
>
>        spin_lock(&receiving_list_lock);
> diff --git a/drivers/staging/pohmelfs/config.c b/drivers/staging/pohmelfs/config.c
> index b6c42cb..327c047 100644
> --- a/drivers/staging/pohmelfs/config.c
> +++ b/drivers/staging/pohmelfs/config.c
> @@ -525,7 +525,7 @@ static void pohmelfs_cn_callback(struct cn_msg *msg, struct netlink_skb_parms *n
>  {
>        int err;
>
> -       if (!cap_raised(current_cap(), CAP_SYS_ADMIN))
> +       if (!IN_ROOT_USER_NS() || !cap_raised(current_cap(), CAP_SYS_ADMIN))
>                return;
>
>        switch (msg->flags) {
> diff --git a/drivers/video/uvesafb.c b/drivers/video/uvesafb.c
> index 7f8472c..94e0e9d 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 (!IN_ROOT_USER_NS() || !cap_raised(current_cap(), CAP_SYS_ADMIN))
>                return;
>
>        if (msg->seq >= UVESAFB_TASKS_MAX)
> diff --git a/include/linux/cred.h b/include/linux/cred.h
> index 4030896..2f75da7 100644
> --- a/include/linux/cred.h
> +++ b/include/linux/cred.h
> @@ -359,9 +359,11 @@ static inline void put_cred(const struct cred *_cred)
>
>  #ifdef CONFIG_USER_NS
>  #define current_user_ns() (current_cred_xxx(user_ns))
> +#define IN_ROOT_USER_NS() (current_user_ns() == &init_user_ns)
>  #else
>  extern struct user_namespace init_user_ns;
>  #define current_user_ns() (&init_user_ns)
> +#define IN_ROOT_USER_NS() (1)
>  #endif
>
>
> --
> 1.7.5.4
>
>
--
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