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    SubjectRe: [PATCH 05/10] user namespace: clamp down users of cap_raised
    From
    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@hallyn.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@canonical.com>
    > Cc: Eric W. Biederman <ebiederm@xmission.com>
    > Cc: Andrew Morgan <morgan@kernel.org>
    > Cc: Vasiliy Kulikov <segoon@openwall.com>
    > Cc: David Howells <dhowells@redhat.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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