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    SubjectRe: [PATCH] userns: Replace netlink uses of cap_raised with capable.
    From
    Acked-by: Andrew G. Morgan <morgan@kernel.org>

    Cheers

    Andrew

    On Tue, Apr 3, 2012 at 7:45 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
    > "Serge E. Hallyn" <serge@hallyn.com> writes:
    >
    >> 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?
    >
    > Absolutely.  Netlink is synchronous.
    >
    > I reread netlink_unicast_kernel() in net/netlink/af_netlink.c while
    > researching this patch.
    >
    > Netlink has been synchronous since 2007.  In a world of perfect
    > knowledge transmission these calls could have been calls to capable
    > from the very beginning.
    >
    >>> 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
    --
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