Re: [PATCH] userns: Replace netlink uses of cap_raised with capable.

Andrew G. Morgan
2012-04-04T04:24:25Z

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