From: "Serge E. Hallyn" <serge@hallyn.com>
To: Aristeu Rozanski <aris@redhat.com>
Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
James Morris <jmorris@namei.org>,
Pavel Emelyanov <xemul@openvz.org>,
Serge Hallyn <serge.hallyn@canonical.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2 0/6] device_cgroup: replace internally whitelist with exception list
Date: Wed, 5 Sep 2012 03:30:02 +0000 [thread overview]
Message-ID: <20120905033002.GG13310@mail.hallyn.com> (raw)
In-Reply-To: <20120904143419.892872876@napanee.usersys.redhat.com>
Quoting Aristeu Rozanski (aris@redhat.com):
> The original model of device_cgroup is having a whitelist where all the
> allowed devices are listed. The problem with this approach is that is
> impossible to have the case of allowing everything but few devices.
>
> The reason for that lies in the way the whitelist is handled internally:
> since there's only a whitelist, the "all devices" entry would have to be
> removed and replaced by the entire list of possible devices but the ones
> that are being denied. Since dev_t is 32 bits long, representing the allowed
> devices as a bitfield is not memory efficient.
>
> This patch replaces the "whitelist" by a "exceptions" list and the default
> policy is kept as "deny_all" variable in dev_cgroup structure.
>
> The current interface determines that whenever "a" is written to devices.allow
> or devices.deny, the entry masking all devices will be added or removed,
> respectively. This behavior is kept and it's what will determine the default
> policy:
>
> # cat devices.list
> a *:* rwm
> # echo a >devices.deny
> # cat devices.list
> # echo a >devices.allow
> # cat devices.list
> a *:* rwm
>
> The interface is also preserved. For example, if one wants to block only access
> to /dev/null:
> # ls -l /dev/null
> crw-rw-rw- 1 root root 1, 3 Jul 24 16:17 /dev/null
> # echo a >devices.allow
> # echo "c 1:3 rwm" >devices.deny
> # cat /dev/null
> cat: /dev/null: Operation not permitted
> # echo >/dev/null
> bash: /dev/null: Operation not permitted
> # mknod /tmp/null c 1 3
> mknod: /tmp/null: Operation not permitted
> # echo "c 1:3 r" >devices.allow
> # cat /dev/null
> # echo >/dev/null
> bash: /dev/null: Operation not permitted
> # mknod /tmp/null c 1 3
> mknod: /tmp/null: Operation not permitted
> # echo "c 1:3 rw" >devices.allow
> # echo >/dev/null
> # cat /dev/null
> # mknod /tmp/null c 1 3
> mknod: /tmp/null: Operation not permitted
> # echo "c 1:3 rwm" >devices.allow
> # echo >/dev/null
> # cat /dev/null
> # mknod /tmp/null c 1 3
> #
>
> v2:
> - stop using simple_strtoul()
> - fix checkpatch warnings
> - rename deny_all to behavior
> - updated documentation
> - added new files to cgroupfs to better reflect the internal state
>
> Documentation/cgroups/devices.txt | 73 ++++--
> security/device_cgroup.c | 443 +++++++++++++++++++++++---------------
> 2 files changed, 333 insertions(+), 183 deletions(-)
>
> --
> Aristeu
Thanks, Aristeu, very nice.
-serge
prev parent reply other threads:[~2012-09-05 3:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-04 14:34 [PATCH v2 0/6] device_cgroup: replace internally whitelist with exception list Aristeu Rozanski
2012-09-04 14:34 ` [PATCH v2 1/6] device_cgroup: add "behavior" in dev_cgroup structure Aristeu Rozanski
2012-09-05 3:00 ` Serge E. Hallyn
2012-09-04 14:34 ` [PATCH v2 2/6] device_cgroup: introduce dev_whitelist_clean() Aristeu Rozanski
2012-09-05 3:03 ` Serge E. Hallyn
2012-09-04 14:34 ` [PATCH v2 3/6] device_cgroup: convert device_cgroup internally to policy + exceptions Aristeu Rozanski
2012-09-05 3:09 ` Serge E. Hallyn
2012-09-04 14:34 ` [PATCH v2 4/6] device_cgroup: stop using simple_strtoul() Aristeu Rozanski
2012-09-05 3:22 ` Serge E. Hallyn
2012-09-04 14:34 ` [PATCH v2 5/6] device_cgroup: rename whitelist to exception list Aristeu Rozanski
2012-09-05 3:24 ` Serge E. Hallyn
2012-09-04 14:34 ` [PATCH v2 6/6] device_cgroup: introduce a new, more consistent interface for device_cgroup Aristeu Rozanski
2012-09-05 3:27 ` Serge E. Hallyn
2012-09-05 3:30 ` Serge E. Hallyn [this message]
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