[patch 01/36] pid: implement ns_of_pid

[Greg KH]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>

commit f9fb860f67b9542cd78d1558dec7058092b57d8e upstream.

A current problem with the pid namespace is that it is easy to do pid
related work after exit_task_namespaces which drops the nsproxy pointer.

However if we are doing pid namespace related work we are always operating
on some struct pid which retains the pid_namespace pointer of the pid
namespace it was allocated in.

So provide ns_of_pid which allows us to find the pid namespace a pid was
allocated in.

Using this we have the needed infrastructure to do pid namespace related
work at anytime we have a struct pid, removing the chance of accidentally
having a NULL pointer dereference when accessing current->nsproxy.

Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: Bastian Blank <bastian@xxxxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxx>
Cc: Nadia Derbey <Nadia.Derbey@xxxxxxxx>
Acked-by: Serge Hallyn <serue@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 include/linux/pid.h |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -123,6 +123,24 @@ extern struct pid *alloc_pid(struct pid_
 extern void free_pid(struct pid *pid);
 
 /*
+ * ns_of_pid() returns the pid namespace in which the specified pid was
+ * allocated.
+ *
+ * NOTE:
+ * 	ns_of_pid() is expected to be called for a process (task) that has
+ * 	an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
+ * 	is expected to be non-NULL. If @pid is NULL, caller should handle
+ * 	the resulting NULL pid-ns.
+ */
+static inline struct pid_namespace *ns_of_pid(struct pid *pid)
+{
+	struct pid_namespace *ns = NULL;
+	if (pid)
+		ns = pid->numbers[pid->level].ns;
+	return ns;
+}
+
+/*
  * the helpers to get the pid's id seen from different namespaces
  *
  * pid_nr()    : global id, i.e. the id seen from the init namespace;

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