On pią, gru 12, 2008 at 08:09:08 -0600, Serge E. Hallyn wrote:> Quoting Grzegorz Nosek (root@xxxxxxxxxxxxxx):> > Hi all,> > > > Is there a good reason for ns_can_attach to restrict moving tasks only> > to direct descentants of the current cgroup? I.e. could the code:> > > > orig = task_cgroup(task, ns_subsys_id);> > if (orig && orig != new_cgroup->parent)> > return -EPERM;> > > > be replaced with:> > > > orig = task_cgroup(task, ns_subsys_id);> > if (orig && !cgroup_is_descendant_of(new_cgroup, orig))> > return -EPERM;> > > > (for a suitable definition of cgroup_is_descendant_of). It would allow> > moving tasks down the cgroup hierarchy more than one level at a time and> > as far as I can see, would pose no additional problems.> > > > Please keep CC'd, I'm not subscribed.> > Well you can always move it down one level at a time, right? :)> > But I can't think of any reason why it would be a problem. So> pls feel free to send a patch.
OK, here's the patch. After some basic testing looks like it's workingas advertised. Please have a look at the patch, esp. the subsys_id part,I'm not sure I got the code/comments all right.
Best regards, Grzegorz Nosek
-------------------------------------->From 8750df0d341c3227a0ed33088602addec003b713 Mon Sep 17 00:00:00 2001From: Grzegorz Nosek <root@xxxxxxxxxxxxxx>Date: Fri, 12 Dec 2008 21:48:09 +0100Subject: [PATCH] Relax ns_can_attach checks to allow attaching to grandchild cgroups
The ns_proxy cgroup allows moving processes to child cgroups only onelevel deep at a time. This commit relaxes this restriction and makes itpossible to attach tasks directly to grandchild cgroups, e.g.:
($pid is in the root cgroup)echo $pid > /cgroup/CG1/CG2/tasks
Previously this operation would fail with -EPERM and would have to beperformed as two steps:echo $pid > /cgroup/CG1/tasksecho $pid > /cgroup/CG1/CG2/tasks
Signed-off-by: Grzegorz Nosek <root@xxxxxxxxxxxxxx>--- include/linux/cgroup.h | 5 +++-- kernel/cgroup.c | 19 ++++++++++++------- kernel/ns_cgroup.c | 9 +++------ 3 files changed, 18 insertions(+), 15 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.hindex 1ba3ded..ab8a5cd 100644--- a/include/linux/cgroup.h+++ b/include/linux/cgroup.h@@ -301,8 +301,9 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen); int cgroup_task_count(const struct cgroup *cgrp); -/* Return true if the cgroup is a descendant of the current cgroup */-int cgroup_is_descendant(const struct cgroup *cgrp);+/* Return true if cgrp is a descendant of the task's cgroup subsystem subsys_id */+int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task,+ int subsys_id); /* Control Group subsystem type. See Documentation/cgroups.txt for details */ diff --git a/kernel/cgroup.c b/kernel/cgroup.cindex 2ae040d..0002fa5 100644--- a/kernel/cgroup.c+++ b/kernel/cgroup.c@@ -3101,28 +3101,33 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys, } /**- * cgroup_is_descendant - see if @cgrp is a descendant of current task's cgrp+ * cgroup_is_descendant - see if @cgrp is a descendant of @task's cgrp * @cgrp: the cgroup in question+ * @task: the task in question+ * @subsys_id: cgroup subsystem id used to determine hierarchy; if negative,+ * use get_first_subsys() *- * See if @cgrp is a descendant of the current task's cgroup in- * the appropriate hierarchy.+ * See if @cgrp is a descendant of @task's cgroup in the appropriate+ * hierarchy. * * If we are sending in dummytop, then presumably we are creating * the top cgroup in the subsystem. * * Called only by the ns (nsproxy) cgroup. */-int cgroup_is_descendant(const struct cgroup *cgrp)+int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task,+ int subsys_id) { int ret; struct cgroup *target;- int subsys_id; if (cgrp == dummytop) return 1; - get_first_subsys(cgrp, NULL, &subsys_id);- target = task_cgroup(current, subsys_id);+ if (subsys_id < 0)+ get_first_subsys(cgrp, NULL, &subsys_id);++ target = task_cgroup(task, subsys_id); while (cgrp != target && cgrp!= cgrp->top_cgroup) cgrp = cgrp->parent; ret = (cgrp == target);diff --git a/kernel/ns_cgroup.c b/kernel/ns_cgroup.cindex 43c2111..5247d84 100644--- a/kernel/ns_cgroup.c+++ b/kernel/ns_cgroup.c@@ -46,21 +46,18 @@ int ns_cgroup_clone(struct task_struct *task, struct pid *pid) static int ns_can_attach(struct cgroup_subsys *ss, struct cgroup *new_cgroup, struct task_struct *task) {- struct cgroup *orig;- if (current != task) { if (!capable(CAP_SYS_ADMIN)) return -EPERM; - if (!cgroup_is_descendant(new_cgroup))+ if (!cgroup_is_descendant(new_cgroup, current, -1)) return -EPERM; } if (atomic_read(&new_cgroup->count) != 0) return -EPERM; - orig = task_cgroup(task, ns_subsys_id);- if (orig && orig != new_cgroup->parent)+ if (!cgroup_is_descendant(new_cgroup, task, ns_subsys_id)) return -EPERM; return 0;@@ -78,7 +75,7 @@ static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss, if (!capable(CAP_SYS_ADMIN)) return ERR_PTR(-EPERM);- if (!cgroup_is_descendant(cgroup))+ if (!cgroup_is_descendant(cgroup, current, -1)) return ERR_PTR(-EPERM); ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);-- 1.5.4.4
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