Re: [PATCH 3/6] user namespace: clamp down users of cap_raised

[Andrew G. Morgan]

Acked-by: Andrew G. Morgan <morgan@xxxxxxxxxx>

Cheers

Andrew

On Fri, Nov 4, 2011 at 3:24 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.
>
> 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@xxxxxxxxxxxxx>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Andrew Morgan <morgan@xxxxxxxxxx>
> Cc: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>
> Cc: David Howells <dhowells@xxxxxxxxxx>
> ---
>  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 af2a250..b7b19b8 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
>
>
> --
> 1.7.0.4
>
>
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