>> /**
>> - * 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
>> *
>> - * 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 ret;
>> struct cgroup *target;
>> @@ -3125,7 +3126,7 @@ int cgroup_is_descendant(const struct cgroup *cgrp)
>> return 1;
>>
>> get_first_subsys(cgrp, NULL, &subsys_id);
>> - target = task_cgroup(current, subsys_id);
>> + target = task_cgroup(task, subsys_id);
>
> What locking prevents *task from vanishing here?
>
As *task is passed to this function, I think it's the caller's responsibility to
insure this ?
>> while (cgrp != target && cgrp!= cgrp->top_cgroup)
>> cgrp = cgrp->parent;
>> ret = (cgrp == target);
>> diff --git a/kernel/ns_cgroup.c b/kernel/ns_cgroup.c
>> index 43c2111..890691a 100644
>> --- a/kernel/ns_cgroup.c
>> +++ b/kernel/ns_cgroup.c
>> @@ -35,7 +35,7 @@ int ns_cgroup_clone(struct task_struct *task, struct pid
>> *pid)
>>
>> /*
>> * Rules:
>> - * 1. you can only enter a cgroup which is a child of your current
>> + * 1. you can only enter a cgroup which is a descendant of your current
>> * cgroup
>> * 2. you can only place another process into a cgroup if
>> * a. you have CAP_SYS_ADMIN
>> @@ -46,21 +46,15 @@ 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))
>> return -EPERM;
>> }
>>
>> - if (atomic_read(&new_cgroup->count) != 0)
>> - return -EPERM;
>> -
>> - orig = task_cgroup(task, ns_subsys_id);
>
> Same question applied to the previous code.
>
It's called by cgroup core, and cgroup guarantees the task won't vanish. (by
get_task_struct)
>> - if (orig && orig != new_cgroup->parent)
>> + if (!cgroup_is_descendant(new_cgroup, task))
>> return -EPERM;
>>
>> return 0;
>> @@ -78,7 +72,7 @@ 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))
>> return ERR_PTR(-EPERM);
>>
>> ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);
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