Oleg Nesterov wrote:
On 08/10, Serge E. Hallyn wrote:
Quoting Pavel Emelyanov ([email protected]):
+/*
+ * the namespaces access rules are:
+ *
+ * 1. only current task is allowed to change tsk->nsproxy pointer or
+ * any pointer on the nsproxy itself
+ *
+ * 2. when accessing (i.e. reading) current task's namespaces - no
+ * precautions should be taken - just dereference the pointers
+ *
+ * 3. the access to other task namespaces is performed like this
+ * rcu_read_lock();
+ * nsproxy = task_nsproxy(tsk);
+ * if (nsproxy != NULL) {
+ * / *
+ * * work with the namespaces here
+ * * e.g. get the reference on one of them
+ * * /
+ * } / *
+ * * NULL task_nsproxy() means that this task is
+ * * almost dead (zombie)
+ * * /
+ * rcu_read_unlock();
And lastly, I guess that the caller to switch_task_namespaces() has
to ensure that new_nsproxy either (1) is the init namespace, (2) is a
brand-new namespace to which noone else has a reference, or (3) the
caller has to hold a reference to the new_nsproxy across the call to
switch_task_namespaces().
As it happens the current calls fit (1) or (2). Again if we happen to
jump into the game of switching a task into another task's nsproxy,
we'll need to be mindful of (3) so that new_nsproxy can't be tossed into
the bin between
if (new)
get_nsproxy(new);
4) Unless tsk == current, get_task_namespaces(tsk) and get_nsproxy(tsk)
are racy even if done under rcu_read_lock().
Yup :)
It is already written in comment that only the current is allowed
to change its nsproxy. I.e. when switch_task_nsproxy() is called
for tsk other than current it's a BUG
Oleg.
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